Emptying and refilling of Ca2+ store in tracheal myocytes as indicated by ACh-evoked currents and contraction

A method for isolating contractile smooth muscle cells from cryopreserved tissue

Multiple techniques have been developed to isolate contractile smooth muscle cells (SMCs) from tissues with varying degrees of success. However, most of these approaches rely on obtaining fresh tissue, which poses logistical challenges. In the present study, we introduce a novel protocol for isolating contractile SMCs from cryopreserved smooth muscle (SM) tissue, thereby enhancing experimental efficiency. This protocol yields abundant viable, spindle-shaped, contractile SMCs that closely resemble those obtained from fresh samples. By analyzing the expression of contractile proteins, we demonstrate that both the isolated SMCs from cryopreserved tissue represent more accurately fresh SM tissue compared with cultured SMCs. Moreover, we demonstrate the importance of a brief incubation step of the tissue in culture medium before cell dissociation to achieve contractile SMCs. Finally, we provide a concise overview of our protocol optimization efforts, along with a summary of previously published methods, which could be valuable for the development of similar protocols for other species.NEW & NOTEWORTHY We report a successful protocol development for isolating contractile smooth muscle cells (SMCs) from cryopreserved tissue reducing the reliance on fresh tissues and providing a readily available source of contractile SMCs. Our findings suggest that SMCs isolated using our protocol maintain their phenotype better compared with cultured SMCs. This preservation of the cellular characteristics, including the expression of key contractile proteins, makes these cells more representative of fresh SM tissue.

Regulation of Airway Smooth Muscle Contraction in Health and Disease

Airway smooth muscle (ASM) extends from the trachea throughout the bronchial tree to the terminal bronchioles. In utero, spontaneous phasic contraction of fetal ASM is critical for normal lung development by regulating intraluminal fluid movement, ASM differentiation, and release of key growth factors. In contrast, phasic contraction appears to be absent in the adult lung, and regulation of tonic contraction and airflow is under neuronal and humoral control. Accumulating evidence suggests that changes in ASM responsiveness contribute to the pathophysiology of lung diseases with lifelong health impacts.Functional assessments of fetal and adult ASM and airways have defined pharmacological responses and signaling pathways that drive airway contraction and relaxation. Studies using precision-cut lung slices, in which contraction of intrapulmonary airways and ASM calcium signaling can be assessed simultaneously in situ, have been particularly informative. These combined approaches have defined the relative importance of calcium entry into ASM and calcium release from intracellular stores as drivers of spontaneous phasic contraction in utero and excitation-contraction coupling.Increased contractility of ASM in asthma contributes to airway hyperresponsiveness. Studies using animal models and human ASM and airways have characterized inflammatory and other mechanisms underlying increased reactivity to contractile agonists and reduced bronchodilator efficacy of β₂-adrenoceptor agonists in severe diseases. Novel bronchodilators and the application of bronchial thermoplasty to ablate increased ASM within asthmatic airways have the potential to overcome limitations of current therapies. These approaches may directly limit excessive airway contraction to improve outcomes for difficult-to-control asthma and other chronic lung diseases.

Assessment of the Airway Smooth Muscle Relaxant Effect of Drotaverine

BACKGROUND

Drotaverine, a type 4 cyclic nucleotide phosphodiesterase (PDE4) inhibitor, blocks the degradation of 3',5'-cyclic adenosine monophosphate. However, published receptor binding data showed that drotaverin also binds to the L-type voltage-operated calcium channel (L-VOCC). Based on these molecular mechanisms of action, a direct and indirect (by blocking the constrictor response) relaxant effect on airway smooth muscle can be predicted, which has not yet been assessed.

SUMMARY

Accordingly, drotaverine and reference agents were tested both on the histamine-, methacholine-, or KCl-induced contraction response and on precontracted guinea pig tracheal preparations. It was found that drotaverine not only relaxed the precontracted tracheal preparations but also decreased mediator-induced contraction. These effects of drotaverine were concentration dependent, with a significantly higher potency on the KCl-induced response, than on either the histamine or methacholine induced one. A similar result was noted for nifedipine. The PDE inhibitor, theophylline, also relaxed the precontracted preparations but was ineffective on the mediator-induced contraction in a physiologically relevant concentration range. Moreover, theophylline did not show selectivity and was the least potent relaxant among the 3 tested molecules. Key Message: These results show that drotaverine is a more potent airway smooth muscle relaxant molecule than theophylline. This enhanced potency on relaxation and inhibition of the constrictor response, at least partly, may be explained by the combined L-VOCC blocking and PDE inhibitory potential of drotaverine.

Sarcoplasmic reticulum Ca(2+) refilling is determined by L-type Ca(2+) and store operated Ca(2+) channels in guinea pig airway smooth muscle

Sarcoplasmic reticulum Ca(2+) refilling (SRREF) is crucial to sustain the agonists induced airway smooth muscle contraction. Nevertheless, its mechanisms have not been clearly described yet, although L-type voltage dependent, store operated, receptor operated channels and the Na(+)/Ca(2+) exchanger in its reverse mode (NCXREV) have been proposed as Ca(2+) handling proteins participating in this process. We found that in guinea pig and bovine tracheal smooth muscle, SRREF induced by caffeine was completely abolished by thapsigargin, even in the presence of Bay K8644, an activator of the L-type Ca(2+) channel. Activation of NCXREV in guinea pig tracheal myocytes increased SRREF in ~70%, while opening of the L-type Ca(2+) channels with Bay K8644 and favoring the capacitative Ca(2+) entry with 2-APB (32 μM) also augmented the SRREF by ~170% and ~71%, respectively. Methoxyverapamil (D-600, an L-type Ca(2+) channel blocker), 2-APB (100 µM, antagonist of the capacitative Ca(2+) entry) and PPADS (NCXREV blocker) diminished the SRREF by ~63%, ~72% and ~31%, respectively. The simultaneous addition of D-600 and 2-APB annulled SRREF. These last results were also seen when carbachol was used instead of caffeine. In tracheal rings, 2-APB and nifedipine abolished the carbachol-induced contraction. We concluded that the sarcoplasmic reticulum Ca(2+) pump is the only mechanism involved in the SRREF and that L-type Ca(2+) voltage dependent and store operated Ca(2+) channels are the principal membranal Ca(2+) handling proteins that provide extracellular Ca(2+) for SRREF and carbachol-induced contraction in the guinea pig airway smooth muscle; NCXREV seems to play a minor role.

A synthetic chloride channel relaxes airway smooth muscle of the rat

Synthetic ion channels may have potential therapeutic applications, provided they possess appropriate biological activities. The present study was designed to examine the ability of small molecule-based synthetic Cl^– channels to modulate airway smooth muscle responsiveness. Changes in isometric tension were measured in rat tracheal rings. Relaxations to the synthetic chloride channel SCC-1 were obtained during sustained contractions to KCl. The anion dependency of the effect of SCC-1 was evaluated by ion substitution experiments. The sensitivity to conventional Cl^– transport inhibitors was also tested. SCC-1 caused concentration-dependent relaxations during sustained contractions to potassium chloride. This relaxing effect was dependent on the presence of extracellular Cl^– and HCO₃⁻. It was insensitive to conventional Cl^– channels/transport inhibitors that blocked the cystic fibrosis transmembrane conductance regulator and calcium-activated Cl^– channels. SCC-1 did not inhibit contractions induced by carbachol, endothelin-1, 5-hydroxytryptamine or the calcium ionophore A23187. SCC-1 relaxes airway smooth muscle during contractions evoked by depolarizing solutions. The Cl^– conductance conferred by this synthetic compound is distinct from the endogenous transport systems for chloride anions.

Caffeine relaxes smooth muscle through actin depolymerization

Caffeine is sometimes used in cell physiological studies to release internally stored Ca(2+). We obtained evidence that caffeine may also act through a different mechanism that has not been previously described and sought to examine this in greater detail. We ruled out a role for phosphodiesterase (PDE) inhibition, since the effect was 1) not reversed by inhibiting PKA or adenylate cyclase; 2) not exacerbated by inhibiting PDE4; and 3) not mimicked by submillimolar caffeine nor theophylline, both of which are sufficient to inhibit PDE. Although caffeine is an agonist of bitter taste receptors, which in turn mediate bronchodilation, its relaxant effect was not mimicked by quinine. After permeabilizing the membrane using β-escin and depleting the internal Ca(2+) store using A23187, we found that 10 mM caffeine reversed tone evoked by direct application of Ca(2+), suggesting it functionally antagonizes the contractile apparatus. Using a variety of molecular techniques, we found that caffeine did not affect phosphorylation of myosin light chain (MLC) by MLC kinase, actin-filament motility catalyzed by MLC kinase, phosphorylation of CPI-17 by either protein kinase C or RhoA kinase, nor the activity of MLC-phosphatase. However, we did obtain evidence that caffeine decreased actin filament binding to phosphorylated myosin heads and increased the ratio of globular to filamentous actin in precontracted tissues. We conclude that, in addition to its other non-RyR targets, caffeine also interferes with actin function (decreased binding by myosin, possibly with depolymerization), an effect that should be borne in mind in studies using caffeine to probe excitation-contraction coupling in smooth muscle.

Airway smooth muscle electrophysiology in a state of flux?

Activation of chloride currents and release of internally sequestered Ca2+ in airway smooth muscle have long been associated with excitation and contraction. Surprisingly, however, two recent publications (Deshpande DA, Wang WC, McIlmoyle EL, Robinett KS, Schillinger RM, An SS, Sham JS, Liggett SB. Nat Med 16: 1299–1304, 2010; Gallos G, Yim P, Chang S, Zhang Y, Xu D, Cook JM, Gerthoffer WT, Emala CW Sr. Am J Physiol Lung Cell Mol Physiol 302: L248–L256, 2012) have linked both events to relaxation. This begs a closer look at our understanding of airway smooth muscle electrophysiology and its contribution to excitation-contraction coupling. This Editorial Focus highlights those two aforementioned studies and several other equally paradoxical findings and proposes some possible reinterpretations of the data and/or new directions of research in which the answers might be found.

A systematic literature review of cerebrospinal fluid biomarkers in delirium

BACKGROUND

Cerebrospinal fluid (CSF) analysis has great potential to advance understanding of delirium pathophysiology.

METHODS

A systematic literature review of CSF studies of DSM or ICD delirium was performed.

RESULTS

In 8 studies of 235 patients, delirium was associated with: elevated serotonin metabolites, interleukin-8, cortisol, lactate and protein, and reduced somatostatin, β-endorphin and neuron-specific enolase. Elevated acetylcholinesterase predicted poor outcome after delirium and higher dopamine metabolites were associated with psychotic features.

CONCLUSIONS

No clear conclusions emerged, but the current literature suggests multiple areas for further investigation with more detailed studies.

Influence of airway wall stiffness and parenchymal tethering on the dynamics of bronchoconstriction

Understanding how tissue remodeling affects airway responsiveness is of key importance, but experimental data bearing on this issue remain scant. We used lung explants to investigate the effects of enzymatic digestion on the rate and magnitude of airway narrowing induced by acetylcholine. To link the observed changes in narrowing dynamics to the degree of alteration in tissue mechanics, we compared our experimental results with predictions made by a computational model of a dynamically contracting elastic airway embedded in elastic parenchyma. We found that treatment of explanted airways with two different proteases (elastase and collagenase) resulted in differential effects on the dynamics of airway narrowing following application of ACh. Histological corroboration of these different effects is manifest in different patterns of elimination of collagen and elastin from within the airway wall and the surrounding parenchyma. Simulations with a computational model of a dynamically contracting airway embedded in elastic parenchyma suggest that elastase exerts its functional effects predominately through a reduction in parenchymal tethering, while the effects of collagenase are more related to a reduction in airway wall stiffness. We conclude that airway and parenchymal remodeling as a result of protease activity can have varied effects on the loads opposing ASM shortening, with corresponding consequences for airway responsiveness.

Sarcoplasmic reticulum function in smooth muscle

The sarcoplasmic reticulum (SR) of smooth muscles presents many intriguing facets and questions concerning its roles, especially as these change with development, disease, and modulation of physiological activity. The SR's function was originally perceived to be synthetic and then that of a Ca store for the contractile proteins, acting as a Ca amplification mechanism as it does in striated muscles. Gradually, as investigators have struggled to find a convincing role for Ca-induced Ca release in many smooth muscles, a role in controlling excitability has emerged. This is the Ca spark/spontaneous transient outward current coupling mechanism which reduces excitability and limits contraction. Release of SR Ca occurs in response to inositol 1,4,5-trisphosphate, Ca, and nicotinic acid adenine dinucleotide phosphate, and depletion of SR Ca can initiate Ca entry, the mechanism of which is being investigated but seems to involve Stim and Orai as found in nonexcitable cells. The contribution of the elemental Ca signals from the SR, sparks and puffs, to global Ca signals, i.e., Ca waves and oscillations, is becoming clearer but is far from established. The dynamics of SR Ca release and uptake mechanisms are reviewed along with the control of luminal Ca. We review the growing list of the SR's functions that still includes Ca storage, contraction, and relaxation but has been expanded to encompass Ca homeostasis, generating local and global Ca signals, and contributing to cellular microdomains and signaling in other organelles, including mitochondria, lysosomes, and the nucleus. For an integrated approach, a review of aspects of the SR in health and disease and during development and aging are also included. While the sheer versatility of smooth muscle makes it foolish to have a "one model fits all" approach to this subject, we have tried to synthesize conclusions wherever possible.

The NADPH oxidase inhibitor diphenyleneiodonium is also a potent inhibitor of cholinesterases and the internal Ca(2+) pump

BACKGROUND AND PURPOSE

Diphenyleneiodonium (DPI) is often used as an NADPH oxidase inhibitor, but is increasingly being found to have unrelated side effects. We investigated its effects on smooth muscle contractions and the related mechanisms.

EXPERIMENTAL APPROACH

We studied isometric contractions in smooth muscle strips from bovine trachea. Cholinesterase activity was measured using a spectrophotometric assay; internal Ca(2+) pump activity was assessed by Ca(2+) uptake into smooth muscle microsomes.

KEY RESULTS

Contractions to acetylcholine were markedly enhanced by DPI (10(-4) M), whereas those to carbachol (CCh) were not, suggesting a possible inhibition of cholinesterase. DPI markedly suppressed contractions evoked by CCh, KCl and 5-HT, and also unmasked phasic activity in otherwise sustained responses. Direct biochemical assays confirmed that DPI was a potent inhibitor of acetylcholinesterase and butyrylcholinesterase (IC(50) approximately 8 x 10(-6) M and 6 x 10(-7) M, respectively), following a readily reversible, mixed non-competitive type of inhibition. The inhibitory effects of DPI on CCh contractions were not mimicked by another NADPH oxidase inhibitor (apocynin), nor the Src inhibitors PP1 or PP2, ruling out an action through the NADPH oxidase signalling pathway. Several features of the DPI-mediated suppression of agonist-evoked responses (i.e. suppression of peak magnitudes and unmasking of phasic activity) are similar to those of cyclopiazonic acid, an inhibitor of the internal Ca(2+) pump. Direct measurement of microsomal Ca(2+) uptake revealed that DPI modestly inhibits the internal Ca(2+) pump.

CONCLUSIONS AND IMPLICATIONS

DPI inhibits cholinesterase activity and the internal Ca(2+) pump in tracheal smooth muscle.

ATP stimulates Ca(2+)-waves and gene expression in cultured human pulmonary fibroblasts

Given that extracellular ATP is markedly elevated in inflammation and is known to modulate fibroblast function, we examined the effects of exogenously added ATP on Ca(2+)-handling and gene expression in human pulmonary fibroblasts. Cells were loaded with the Ca(2+)-indicator dye fluo-4 and studied using confocal fluorimetry. Standard RT-PCR was used to probe gene expression. ATP (10(-5)M) evoked recurring Ca(2+)-waves which were completely occluded by cyclopiazonic acid (depletes the internal Ca(2+)-store) or the phospholipase inhibitor U73122. Pretreatment with ryanodine (10(-5)M), however, had no effect on the ATP-evoked responses. Regarding the receptor through which ATP acted, we found the ATP-response to be mimicked by UTP or ADP but not by adenosine or alpha,beta-methylene-ATP, and to be blocked by the purinergic receptor blocker PPADS. The ATP-evoked response was greater and longer lasting within the nucleus than in the non-nuclear portion of the cytosol. RT-PCR showed that ATP also rapidly and dramatically increased gene expression of P2Y(4) receptors, the cytokine TGF-beta (an important modulator of wound repair) and two matrix proteins (collagen A1 and fibronectin) approximately 4-5 times above baseline: this increase was not significantly affected by ryanodine but was abolished by PPADS. We conclude that, in human pulmonary fibroblasts, ATP acts upon P2Y receptors to liberate internal Ca(2+) through ryanodine-insensitive channels, leading to a Ca(2+)-wave which courses throughout the cell and modulates gene expression.

Airway smooth muscle dynamics: a common pathway of airway obstruction in asthma

Excessive airway obstruction is the cause of symptoms and abnormal lung function in asthma. As airway smooth muscle (ASM) is the effecter controlling airway calibre, it is suspected that dysfunction of ASM contributes to the pathophysiology of asthma. However, the precise role of ASM in the series of events leading to asthmatic symptoms is not clear. It is not certain whether, in asthma, there is a change in the intrinsic properties of ASM, a change in the structure and mechanical properties of the noncontractile components of the airway wall, or a change in the interdependence of the airway wall with the surrounding lung parenchyma. All these potential changes could result from acute or chronic airway inflammation and associated tissue repair and remodelling. Anti-inflammatory therapy, however, does not "cure" asthma, and airway hyperresponsiveness can persist in asthmatics, even in the absence of airway inflammation. This is perhaps because the therapy does not directly address a fundamental abnormality of asthma, that of exaggerated airway narrowing due to excessive shortening of ASM. In the present study, a central role for airway smooth muscle in the pathogenesis of airway hyperresponsiveness in asthma is explored.

Airway smooth muscle as a target of asthma therapy: history and new directions

Ultimately, asthma is a disease characterized by constriction of airway smooth muscle (ASM). The earliest approach to the treatment of asthma comprised the use of xanthines and anti-cholinergics with the later introduction of anti-histamines and anti-leukotrienes. Agents directed at ion channels on the smooth muscle membrane (Ca2+ channel blockers, K+ channel openers) have been tried and found to be ineffective. Functional antagonists, which modulate intracellular signalling pathways within the smooth muscle (beta-agonists and phosphodiesterase inhibitors), have been used for decades with success, but are not universally effective and patients continue to suffer with exacerbations of asthma using these drugs. During the past several decades, research energies have been directed into developing therapies to treat airway inflammation, but there have been no substantial advances in asthma therapies targeting the ASM. In this manuscript, excitation-contraction coupling in ASM is addressed, highlighting the current treatment of asthma while proposing several new directions that may prove helpful in the management of this disease.

Apoptosis inhibition in T cells triggers the expression of proinflammatory cytokines--implications for the CNS

Stimulation of death receptors such as CD95 or TNF-R1 results in rapid onset of apoptosis. Here we show that inhibition of death receptor-induced apoptosis by the broad range caspase inhibitor ZVAD causes a switch from apoptotic to proinflammatory signaling. In previous studies we have reported that caspase inhibitors induce expression of various proinflammatory cytokines in CD95-stimulated primary T cells, such as TNF-alpha, IFN-gamma and GM-CSF. In this study we provide further evidence for the proinflammatory activity of CD95. Stimulation of CD95 by agonistic antibodies (7C11) resulted in expression of IL-2 in primary T cells, which was further enhanced when caspase activity was blocked by ZVAD. Moreover, CD95 triggered expression of IL-4 and IL-8 when caspase activity was inhibited, but not in the absence of ZVAD. Our findings are of significant importance for the CNS as changes in the cytokine pattern in the periphery affects the entry of various immune cells into the brain. Moreover, invading activated T cells can also directly influence the cytokine profile within the brain, triggering signaling cascades that eventually lead to neuronal cell death. The use of caspase inhibitors to prevent apoptotic cell death should be carefully evaluated in the management of systemic and CNS diseases.

IL-4 inhibits calcium transients in bovine trachealis cells by a ryanodine receptor-dependent mechanism

IL-4 and IL-13 have important roles in the pathogenesis of asthma. A novel finding was that brief exposure of airway smooth muscle cells to IL-4 inhibited carbachol-stimulated calcium transients. We hypothesized that IL-4 inhibits transients by decreasing calcium store content and tested this by measuring the effects of IL-4 on transients induced by a nonspecific ionophore. Bovine trachealis cells were loaded with fura 2-AM, and cytosolic calcium concentrations ([Ca2+]i) were measured in single cells by digital microscopy. Stimulation (S1) with carbachol (10 microM) caused rapid, transient increases in [Ca2+]i to 1299 +/- 355 nM (n=5). After recovery of calcium stores, stimulation (S2) of the same cells with ionomycin (10 microM), in the absence of extracellular calcium, also increased [Ca2+]i to give S2/S1 ratio of 1.03 +/- 0.29. However, after 20 min of IL-4 (50 ng/ml), but not IL-13, ionomycin transients were decreased to 0.50 +/- 0.16 (S2/S1, P=0.02, n=6). IL-4 did not inhibit transients with ryanodine receptor calcium release channels (RyR) blocked by ryanodine (200 microM) (S2/S1=1.01+/-0.11) but still did in the presence of 8-bromo cyclic ADP-ribose, an antagonist of cyclic ADP-ribose (cADPR) signaling at RyR (S2/S1=0.48+/-0.13). Together, findings suggest that IL-4 decreases intracellular calcium stores by mechanisms dependent on RyR, but not on cADPR signaling.

Ion channels in smooth muscle: regulators of intracellular calcium and contractility

Smooth muscle (SM) is essential to all aspects of human physiology and, therefore, key to the maintenance of life. Ion channels expressed within SM cells regulate the membrane potential, intracellular Ca2+ concentration, and contractility of SM. Excitatory ion channels function to depolarize the membrane potential. These include nonselective cation channels that allow Na+ and Ca2+ to permeate into SM cells. The nonselective cation channel family includes tonically active channels (Icat), as well as channels activated by agonists, pressure-stretch, and intracellular Ca2+ store depletion. Cl--selective channels, activated by intracellular Ca2+ or stretch, also mediate SM depolarization. Plasma membrane depolarization in SM activates voltage-dependent Ca2+ channels that demonstrate a high Ca2+ selectivity and provide influx of contractile Ca2+. Ca2+ is also released from SM intracellular Ca2+ stores of the sarcoplasmic reticulum (SR) through ryanodine and inositol trisphosphate receptor Ca2+ channels. This is part of a negative feedback mechanism limiting contraction that occurs by the Ca2+-dependent activation of large-conductance K+ channels, which hyper polarize the plasma membrane. Unlike the well-defined contractile role of SR-released Ca2+ in skeletal and cardiac muscle, the literature suggests that in SM Ca2+ released from the SR functions to limit contractility. Depolarization-activated K+ chan nels, ATP-sensitive K+ channels, and inward rectifier K+ channels also hyperpolarize SM, favouring relaxation. The expression pattern, density, and biophysical properties of ion channels vary among SM types and are key determinants of electrical activity, contractility, and SM function.

Mechanisms of interleukin-4 effects on calcium signaling in airway smooth muscle cells

In airway smooth muscle cells, interleukin (IL)-4 inhibited both carbachol- and caffeine-induced calcium mobilization from the sarcoplasmic reticulum (SR). Because of the known signaling pathways for IL-4 and importance of calcium uptake in maintaining SR calcium stores shared by agonists and caffeine, it was hypothesized that this rapid inhibitory effect might depend on phosphatidylinositol 3-kinase (PI3K) and on inhibition of calcium uptake by the SR. Enzyme-dispersed bovine trachealis cells were loaded with Fura-2/acetoxymethyl ester, and changes in cytosolic calcium were imaged in single cells. Cells were pretreated with inhibitors of PI3K, either wortmannin (100 nM), LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one] (50 microM), or deguelin (100 nM). Calcium transients in response to carbachol (10 microM) were significantly decreased to 0.34 +/- 0.10 of control after 20-min treatment with IL-4 but were 1.10 +/- 0.26 and 1.08 +/- 0.23 when wortmannin or deguelin, respectively, was added along with IL-4. LY294002 alone had nonspecific effects on transients. In other experiments, cyclopiazonic acid (CPA) (5 microM), an inhibitor of SR calcium uptake, decreased carbachol-stimulated transients within 4 min to 0.83 +/- 0.08 of control (n = 6). However, for cells treated with IL-4 (50 ng/ml) plus CPA, transients decreased significantly more, to only 0.51 +/- 0.05 (n = 6; p < 0.05). Longer exposures to IL-4 and a higher concentration of CPA (30 microM) gave similar results. It was concluded that IL-4 did not inhibit transients in the presence of PI3K antagonists but that it did in the presence of CPA. This suggested that IL-4 inhibited calcium transients by mechanisms dependent upon a wortmannin-sensitive PI3K but not by inhibition of calcium uptake into the SR.

Characterization of intracellular Ca(2+) stores in gallbladder smooth muscle

The existence of functionally distinct intracellular Ca(2+) stores has been proposed in some types of smooth muscle. In this study, we sought to examine Ca(2+) stores in the gallbladder by measuring intracellular Ca(2+) concentration ([Ca(2+)](i)) in fura 2-loaded isolated myocytes, membrane potential in intact smooth muscle, and isometric contractions in whole mount preparations. Exposure of isolated myocytes to 10 nM CCK caused a transient elevation in [Ca(2+)](i) that persisted in Ca(2+)-free medium and was inhibited by 2-aminoethoxydiphenylborane (2-APB). Application of caffeine induced a rapid spike-like elevation in [Ca(2+)](i) that was insensitive to 2-APB but was abolished by pretreatment with 10 muM ryanodine. These data support the idea that both inositol trisphosphate (IP(3)) receptors (IP(3)R) and ryanodine receptors (RyR) are present in this tissue. When caffeine was applied in Ca(2+)-free solution, the [Ca(2+)](i) transients decreased as the interval between Ca(2+) removal and caffeine application was increased, indicating a possible leakage of Ca(2+) in these stores. The refilling of caffeine-sensitive stores involved sarcoendoplasmic reticulum Ca(2+)-ATPase activation, similar to IP(3)-sensitive stores. The moderate Ca(2+) elevation caused by CCK was associated with a gallbladder contraction, but caffeine or ryanodine failed to induce gallbladder contraction. Nevertheless, caffeine caused a concentration-dependent relaxation in gallbladder strips either under resting tone conditions or precontracted with 1 muM CCK. Taken together, these results suggest that, in gallbladder smooth muscle, multiple pharmacologically distinct Ca(2+) pools do not exist, but IP(3)R and RyR must be spatially separated because Ca(2+) release via these pathways leads to opposite responses.

Pharmacological modulation of sarcoplasmic reticulum function in smooth muscle

The sarco/endoplasmic reticulum (SR/ER) is the primary storage and release site of intracellular calcium (Ca2+) in many excitable cells. The SR is a tubular network, which in smooth muscle (SM) cells distributes close to cellular periphery (superficial SR) and in deeper aspects of the cell (deep SR). Recent attention has focused on the regulation of cell function by the superficial SR, which can act as a buffer and also as a regulator of membrane channels and transporters. Ca2+ is released from the SR via two types of ionic channels [ryanodine- and inositol 1,4,5-trisphosphate-gated], whereas accumulation from thecytoplasm occurs exclusively by an energy-dependent sarco-endoplasmic reticulum Ca2+-ATPase pump (SERCA). Within the SR, Ca2+ is bound to various storage proteins. Emerging evidence also suggests that the perinuclear portion of the SR may play an important role in nuclear transcription. In this review, we detail the pharmacology of agents that alter the functions of Ca2+ release channels and of SERCA. We describe their use and selectivity and indicate the concentrations used in investigating various SM preparations. Important aspects of cell regulation and excitation-contractile activity coupling in SM have been uncovered through the use of such activators and inhibitors of processes that determine SR function. Likewise, they were instrumental in the recent finding of an interaction of the SR with other cellular organelles such as mitochondria. Thus, an appreciation of the pharmacology and selectivity of agents that interfere with SR function in SM has greatly assisted in unveiling the multifaceted nature of the SR.

Enhanced Myosin Phosphatase and Ca2+-Uptake Mediate Adrenergic Relaxation of Airway Smooth Muscle

We examined the mechanisms underlying relaxations evoked by isoproterenol (Iso) in isolated porcine, bovine, or human tracheal and bronchial tissues (TSM and BSM, respectively). Iso had little effect against contractions evoked by high KCl, indicating that it does not directly suppress voltage-dependent Ca(2+)-influx nor directly inhibit myosin light chain kinase. Furthermore, Iso was equally potent against carbachol (CCh) contractions in the presence versus absence of nifedipine (10(-6) M), establishing that the primary action of Iso is not through membrane hyperpolarization. However, Iso relaxations in porcine/bovine BSM were significantly suppressed by inhibitors of the internal Ca(2+) pump (cyclopiazonic acid; 10(-5) M) or of myosin light chain phosphatase (calyculin; 10(-6) M). Myosin light chain phosphatase activity was assayed directly (using (32)P-labeled myosin) and found to be enhanced in a time- and concentration-dependent fashion by Iso. Iso relaxations in human airway tissues, on the other hand, were not significantly affected by either calyculin or cyclopiazonic acid. Thus, we conclude that Iso acts largely in a voltage-independent fashion: in nonhuman airways, this involves enhanced Ca(2+) pump activity (to decrease [Ca(2+)](i)) and myosin light chain phosphatase activation (to decrease Ca(2+)-sensitivity of the contractile apparatus), whereas in human airways the underlying mechanisms are still unclear.

Electrophysiological effects of erythromycin, but lack of mechanical effects, in airway smooth muscle

The antibiotic erythromycin has been shown to modulate a variety of electrophysiological and mechanical responses in many cell types. We investigated whether it did so in airway smooth muscle using standard patch clamp, fura-2 fluorimetric and organ bath techniques. Erythromycin (10(-4) M) evoked a small transient inward current with reversal potential and time-course similar to that of the Ca2+-dependent Cl- currents seen in these cells. Unlike its effects in other cell types, however, it did not alter basal [Ca2+]i, voltage-dependent Ca2+ currents, nor mechanical tone at rest, nor the corresponding responses to cholinergic stimulation (membrane currents; release of internally sequestered Ca2+, nor contractions evoked by neural stimulation or exogenously added cholinergic agonist). In conclusion, erythromycin does exert interesting electrophysiological actions in airway smooth muscle, but does not alter mechanical activity as it has been shown to do elsewhere.

Evidence for the expression of transient receptor potential proteins in guinea pig airway smooth muscle cells

OBJECTIVE

The present study investigates the expression of transient receptor potential (TRPC) proteins in airway smooth muscle (ASM) cells in order to determine whether these proteins may be candidate molecular counterparts of plasma membrane Ca2+-permeable channels involved in the contraction of ASM.

METHODS

Expression of TRPC mRNA was detected using specific primers and RT-PCR. Expression of the TRPC1, TRPC3 and TRPC6 proteins was detected using antibodies in immunoprecipitation and Western blot.

RESULTS

Guinea pig ASM cells exhibited thapsigargin- and acetylcholine-initiated Ca2+ inflow but none by 1-oleoyl-2-acetyl-sn-glycerol. mRNA encoding each of the TRPC1 to TRPC6 proteins was detected in ASM cells. mRNA encoding TRPC1, TRPC3, TRPC4 and TRPC6 was detected in ASM cells at a concentration approximately equivalent to that in guinea pig brain. mRNA encoding TRPC2 and TRPC5 was more abundant in ASM cells than in brain. The TRPC1 protein, but not the TRPC3 or TRPC6 proteins, was detected in extracts of ASM cells, while all three proteins were detected in brain.

CONCLUSION

The results provide evidence for a low level of expression of the TRPC1 to TRPC6 proteins in ASM cells. These proteins may function as store-operated Ca2+ and/or second messenger-activated non-selective cation channels in ASM cells.

[Ca2+]i changes in guinea pig tracheal smooth muscle cells in culture: effects of Na+ and ouabain

The objective of this work was to confirm that the contractile effects of ouabain and Na(+)-free solutions in guinea pig tracheal rings are associated with increments in the cytosolic free Ca2+ concentration ([Ca2+]i) in cultured tracheal smooth muscle (TSM) cells. Cultured cells were alpha-actin positive. Histamine (50 microM) and Na(+)-free solution elicited a transient increase in [Ca2+]i, while the responses to thapsigargin (1 microM) and ouabain (1 mM) were long lasting. However, carbachol (10, 200, and 500 mM) and high K(+)-solution produced no effect on [Ca2+]i, suggesting that cultured guinea pig TSM cells display a phenotype change but maintain some of the tracheal rings physiological properties. The transient rise in [Ca2+]i in response to the absence of extracellular Na+ and the effect of ouabain may indicate the participation of the Na(+)/Ca2+ exchanger (NCX) in the regulation of [Ca2+]i.

Ionic mechanisms and Ca(2+) regulation in airway smooth muscle contraction: do the data contradict dogma?

In general, excitation-contraction coupling in muscle is dependent on membrane depolarization and hyperpolarization to regulate the opening of voltage-dependent Ca(2+) channels and, thereby, influence intracellular Ca(2+) concentration ([Ca(2+)](i)). Thus Ca(2+) channel blockers and K(+) channel openers are important tools in the arsenals against hypertension, stroke, and myocardial infarction, etc. Airway smooth muscle (ASM) also exhibits robust Ca(2+), K(+), and Cl(-) currents, and there are elaborate signaling pathways that regulate them. It is easy, then, to presume that these also play a central role in contraction/relaxation of ASM. However, several lines of evidence speak to the contrary. Also, too many researchers in the ASM field view the sarcoplasmic reticulum as being centrally located and displacing its contents uniformly throughout the cell, and they have focused almost exclusively on the initial single [Ca(2+)] spike evoked by excitatory agonists. Several recent studies have revealed complex spatial and temporal heterogeneity in [Ca(2+)](i), the significance of which is only just beginning to be appreciated. In this review, we will compare what is known about ion channels in ASM with what is believed to be their roles in ASM physiology. Also, we will examine some novel ionic mechanisms in the context of Ca(2+) handling and excitation-contraction coupling in ASM.

Airway hyperresponsiveness and calcium handling by smooth muscle: a "deeper look"

We propose that abnormal calcium handling by the airway smooth muscle may be an important determinant of airway hyperresponsiveness. The amplitude, frequency, or localization of Ca(2+) oscillations in the smooth muscle may determine the degree of airway sensitivity and reactivity, which are characteristic features of asthma.

The role of the L-type Ca(2+) channel in refilling functional intracellular Ca(2+) stores in guinea-pig detrusor smooth muscle

The transient rise of intracellular Ca(2+) in detrusor smooth muscle cells is due to the release of Ca(2+) from intracellular stores. However, it is not known how store refilling is maintained at a constant level to ensure constancy of the contractile response. The aim of these experiments was to characterise the role of L-type Ca(2+) channels in refilling. Experiments used isolated guinea-pig detrusor myocytes and store Ca(2+) content was estimated by measuring the magnitude of change to the intracellular [Ca(2+)] ([Ca(2+)](i)) after application of caffeine or carbachol using epifluorescence microscopy. Membrane potential was controlled when necessary by voltage clamp. After Ca(2+) stores were emptied they refilled with an exponential time course, with a time constant of 88 s. The value of the time constant was similar to that of the undershoot of [Ca(2+)](i) following store Ca(2+) release. The degree of store filling was enhanced by maintained depolarisation, or by transient depolarising pulses, and attenuated by L-type Ca(2+) channel antagonists. Inhibition of the sarcoplasmic reticular Ca(2+)-ATPase prevented refilling. Reduction of the resting [Ca(2+)](i) was accompanied by membrane depolarisation; under voltage clamp reduction of [Ca(2+)](i) decreased the number and magnitude of spontaneous transient outward currents. Ca(2+) release from intracellular stores, elicited by caffeine or carbachol, is independent of membrane potential under physiological conditions. However, store refilling occurs via Ca(2+) influx through L-type Ca(2+) channels. Ca(2+) influx is regulated by a feedback mechanism whereby a fall of [Ca(2+)](i) reduces the activity of Ca(2+)-activated K(+) channels, causing cell depolarisation and an enhancement of L-type Ca(2+) channel conductance.

Muscarinic excitation-contraction coupling mechanisms in tracheal and bronchial smooth muscles

We investigated the mechanisms underlying muscarinic excitation-contraction coupling in canine airway smooth muscle using organ bath, fura 2 fluorimetric, and patch-clamp techniques. Cyclopiazonic acid (CPA) augmented the responses to submaximal muscarinic stimulation in both tracheal (TSM) and bronchial smooth muscles (BSM), consistent with disruption of the barrier function of the sarcoplasmic reticulum. During maximal stimulation, however, CPA evoked substantial relaxation in TSM but not BSM. CPA reversal of carbachol tone persisted in the presence of tetraethylammoium or high KCl, suggesting that hyperpolarization is not involved; CPA relaxations were absent in tissues preconstricted with KCl alone or by permeabilization with beta-escin, ruling out a nonspecific effect on the contractile apparatus. Peak contractions were sensitive to inhibitors of tyrosine kinase (genistein) or Rho kinase (Y-27632). Sustained responses were dependent on Ca(2+) influx in TSM but not BSM; this influx was sensitive to Ni(2+) but not La(3+). In conclusion, there are several mechanisms underlying excitation-contraction coupling in airway smooth muscle, the relative importance of which varies depending on tissue and degree of stimulation.

Effects of cyclopiazonic acid on cytosolic calcium in bovine airway smooth muscle cells

In many cells, inhibition of sarcoplasmic reticulum (SR) Ca2+-ATPase activity induces a steady-state increase in cytosolic calcium concentration ([Ca2+]i) that is sustained by calcium influx. The goal was to characterize the response to inhibition of SR Ca2+-ATPase activity in bovine airway smooth muscle cells. Cells were dispersed from bovine trachealis and loaded with fura 2-AM (0.5 microM) for imaging of single cells. Cyclopiazonic acid (CPA; 5 microM) inhibited refilling of both caffeine- and carbachol-sensitive calcium stores. In the presence of extracellular calcium, CPA caused a transient increase in [Ca2+]i from 166 +/- 11 to 671 +/- 100 nM, and then [Ca2+]i decreased to a sustained level (CPA plateau; 236 +/- 19 nM) significantly above basal. The CPA plateau spontaneously declined toward basal levels after 10 min and was attenuated by discharging intracellular calcium stores. When CPA was applied during sustained stimulation with caffeine or carbachol, decreases in [Ca2+]i were observed. We concluded that the CPA plateau depended on the presence of SR calcium and that SR Ca2+-ATPase activity contributed to sustained increases in [Ca2+]i during stimulation with caffeine and, to a lesser extent, carbachol.

Potential novel uses of thalidomide: focus on palliative care

Thalidomide, after being banned from the market in the early 1960s because of the worldwide teratogenesis disaster, is currently being rediscovered because of its multiple therapeutic effects in various serious diseases and symptoms. Original studies examined the anxiolytic, mild hypnotic, anti-emetic and adjuvant analgesic properties of this drug. Subsequently, thalidomide was found to be highly effective in managing the cutaneous manifestations of leprosy (erythema nodosum leprosum) and even to be superior to aspirin (acetylsalicylic acid) in controlling leprosy-associated fever. Recent research shows promising results with thalidomide in patients with progressive bodyweight loss related to advanced cancer and HIV infection. Thalidomide therapy of diseases such as tuberculosis, sarcoidosis, aphthous ulcers in HIV syndrome and Behcet's disease, rheumatoid arthritis, multiple myeloma, graft-versus-host disease, pyoderma gangrenosum, inflammatory bowel disease, Sjögren's syndrome, lupus erythematosus and a variety of solid tumours is currently being explored. Furthermore, in preliminary studies, thalidomide has been found to be effective in several syndromes related to advanced cancer, such as the cancer cachexia syndrome, chronic nausea, insomnia, profuse sweating and pain. Whether thalidomide has a therapeutic effect on neoplastic fever has yet to be elucidated. These intriguing features make the use of the drug potentially attractive for palliative care. In addition, by a distinct mechanism of action compared with most other drugs, thalidomide offers the possibility of combined treatment with other agents with non-overlapping toxicities. The mechanism of action of thalidomide is probably based on the suppression of tumour necrosis factor-alpha and the modulation of interleukins. However, it is not possible to identify a single dominant mechanism, since the action of cytokines and the effect of thalidomide appear to be complex. This review article discusses the original uses and teratogenic effects of thalidomide within its historical context and, linking recent research at the molecular level with clinical findings, aims to provide the reader with insight into the current understanding of its biological actions, toxicities and potential benefits.

NO(+) but not NO radical relaxes airway smooth muscle via cGMP-independent release of internal Ca(2+)

We compared the effects of two redox forms of nitric oxide, NO(+) [liberated by S-nitroso-N-acetyl-penicillamine (SNAP)] and NO. [liberated by 3-morpholinosydnonimine (SIN-1) in the presence of superoxide dismutase], on cytosolic concentration of Ca(2+) ([Ca(2+)](i); single cells) and tone (intact strips) obtained from human main stem bronchi and canine trachealis. SNAP evoked a rise in [Ca(2+)](i) that was unaffected by removing external Ca(2+) but was markedly reduced by depleting the internal Ca(2+) pool using cyclopiazonic acid (10(-5) M). Dithiothreitol (1 mM) also antagonized the Ca(2+) transient as well as the accompanying relaxation. SNAP attenuated responses to 15 and 30 mM KCl but not those to 60 mM KCl, suggesting the involvement of an electromechanical coupling mechanism rather than a direct effect on the contractile apparatus or on Ca(2+) channels. SNAP relaxations were sensitive to charybdotoxin (10(-7) M) or tetraethylammonium (30 mM) but not to 4-aminopyridine (1 mM). Neither SIN-1 nor 8-bromoguanosine 3',5'-cyclic monophosphate had any significant effect on resting [Ca(2+)](i), although both of these agents were able to completely reverse tone evoked by carbachol (10(-7) M). We conclude that NO(+) causes release of internal Ca(2+) in a cGMP-independent fashion, leading to activation of Ca(2+)-dependent K(+) channels and relaxation, whereas NO. relaxes the airways through a cGMP-dependent, Ca(2+)-independent pathway.

Ca(2+)-dependent Cl(-) channels in mouse and rabbit aortic smooth muscle cells: regulation by intracellular Ca(2+) and NO

Ca(2+)-dependent Cl(-) (Cl(-)(Ca)) channels and their regulation by intracellular Ca(2+) concentration ([Ca(2+)](i)) and nitric oxide (NO) were characterized in mouse and rabbit aortic smooth muscle cells (SMC) using patch clamp and fura 2 imaging. Single channels (1. 8 pS) and whole cell Cl(-)(Ca) currents were activated by caffeine-induced Ca(2+) release. Single Cl(-)(Ca) channels were also activated by >/=200 nM Ca(2+) in inside-out membrane patches and remained active for >5 min in </=1 microM Ca(2+) but showed rapid rundown in 2 mM Ca(2+). Authentic NO or S-nitroso-N-acetylpenicillamine (SNAP) did not affect their activation or rundown in inside-out patches. In the whole cell, SNAP (100 microM) and 8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (50 microM) did not affect Cl(-)(Ca) current, but at a higher concentration SNAP (1 mM) induced a sustained [Ca(2+)](i) rise, accompanied by a dramatic decrease in caffeine-induced Ca(2+) release and Cl(-)(Ca) current. These results indicate that 1) mouse and rabbit aortic SMC possess 1.8-pS Cl(-)(Ca) channels that are activated by Ca(2+) release from the stores, 2) both activation and rundown of single Cl(-)(Ca) channels depend on [Ca(2+)](i), and 3) NO does not affect Cl(-)(Ca) channels directly or via cGMP but can inhibit their activation indirectly by decreasing Ca(2+) release from the stores.

Chemokines in the CNS: plurifunctional mediators in diverse states

The past decade has witnessed the remarkable ascendance of chemokines as pivotal regulatory molecules in cellular communication and trafficking. Evidence increasingly implicates chemokines and chemokine receptors as plurifunctional molecules that have a significant impact on the CNS. Initially, these molecules were found to be involved in the pathogenesis of many important neuroinflammatory diseases that range from multiple sclerosis and stroke to HIV encephalopathy. However, more-recent studies have fuelled the realization that, in addition to their role in pathological states, chemokines and their receptors have an important role in cellular communication in the developing and the normal adult CNS. For example, stromal-cell-derived factor 1, which is synthesized constitutively in the developing brain, has an obligate role in neurone migration during the formation of the granule-cell layer of the cerebellum. Many chemokines are capable of directly regulating signal-transduction pathways that are involved in a variety of cellular functions, which range from synaptic transmission to growth. Clearly, the potential use of chemokines and their receptors as targets for therapeutic intervention in CNS disease might now have to be considered in the context of the broader physiological functions of these molecules.

Superficial buffer barrier and preferentially directed release of Ca2+ in canine airway smooth muscle

We examined cytosolic concentration of Ca2+ ([Ca2+]i) in canine airway smooth muscle using fura 2 fluorimetry (global changes in [Ca2+]i), membrane currents (subsarcolemmal [Ca2+]i), and contractions (deep cytosolic [Ca2+]i). Acetylcholine (10(-4) M) elicited fluorimetric, electrophysiological, and mechanical responses. Caffeine (5 mM), ryanodine (0.1-30 microM), and 4-chloro-3-ethylphenol (0.1-0.3 mM), all of which trigger Ca2+-induced Ca2+ release, evoked Ca2+ transients and membrane currents but not contractions. The sarcoplasmic reticulum (SR) Ca2+-pump inhibitor cyclopiazonic acid (CPA; 10 microM) evoked Ca2+ transients and contractions but not membrane currents. Caffeine occluded the response to CPA, whereas CPA occluded the response to acetylcholine. Finally, KCl contractions were augmented by CPA, ryanodine, or saturation of the SR and reduced when SR filling state was decreased before exposure to KCl. We conclude that 1) the SR forms a superficial buffer barrier dividing the cytosol into functionally distinct compartments in which [Ca2+]i is regulated independently; 2) Ca2+-induced Ca2+ release is preferentially directed toward the sarcolemma; and 3) there is no evidence for multiple, pharmacologically distinct Ca2+ pools.

Divergent differentiation paths in airway smooth muscle culture: induction of functionally contractile myocytes

We tested the hypothesis that prolonged serum deprivation would allow a subset of cultured airway myocytes to reacquire the abundant contractile protein content, marked shortening capacity, and elongated morphology characteristic of contractile cells within intact tissue. Passage 1 or 2 canine tracheal smooth muscle (SM) cells were grown to confluence, then serum deprived for up to 19 days. During serum deprivation, two differentiation pathways emerged. One-sixth of the cells developed an elongated morphology and aligned into bundles. Elongated myocytes contained cables of contractile myofilaments, dense bodies, gap junctions, and membrane caveoli, ultrastructural features of contractile SM in tissue. These cells immunostained intensely for SM alpha-actin, SM myosin heavy chain (MHC), and SM22 (an SM-specific actin-binding protein), and Western analysis of culture lysates disclosed 1.8 (SM alpha-actin)-, 7.7 (SM MHC)-, and 5.8 (SM22)-fold protein increases during serum deprivation. Immunoreactive M3 muscarinic receptors were present in dense foci distributed throughout elongated, SM MHC-positive myocytes. ACh (10(-3) M) induced a marked shortening (59.7 +/- 14.4% of original length) in 62% of elongated myocytes made semiadherent by gentle proteolytic digestion, and membrane bleb formation (a consequence of contraction) occurred in all stimulated cells that remained adherent and so did not shorten. Cultured airway myocytes that did not elongate during serum deprivation instead became short and flattened, lost immunoreactivity for contractile proteins, lacked the M3 muscarinic-receptor expression pattern seen in elongated cells, and exhibited no contractile response to ACh. Thus we demonstrate that prolonged serum deprivation induces distinct differentiation pathways in confluent cultured tracheal myocytes and that one subpopulation acquires an unequivocally functional contractile phenotype in which structure and function resemble contractile myocytes from intact tissue.

A method for isolating adult and neonatal airway smooth muscle cells and measuring shortening velocity

Methods are described for isolating smooth muscle cells from the tracheae of adult and neonatal sheep and measuring the single-cell shortening velocity. Isolated cells were elongated, Ca2+ tolerant, and contracted rapidly and substantially when exposed to cholinergic agonists, KCl, serotonin, or caffeine. Adult cells were longer and wider than preterm cells. Mean cell length in 1.6 mM CaCl2 was 194 +/- 57 (SD) microm (n = 66) for adult cells and 93 +/- 32 microm (n = 20) for preterm cells (P < 0.05). Mean cell width at the widest point of the adult cells was 8.2 +/- 1.8 microm (n = 66) and 5.2 +/- 1.5 microm (n = 20) for preterm cells (P < 0.05). Cells were loaded into a perfusion dish maintained at 35 degreesC and exposed to agonists, and contractions were videotaped. Cell lengths were measured from 30 video frames and plotted as a function of time. Nonlinear fitting of cell length to an exponential model gave shortening velocities faster than most of those reported for airway smooth muscle tissues. For a sample of 10 adult and 10 preterm cells stimulated with 100 microM carbachol, mean (+/- SD) shortening velocity of the preterm cells was not different from that of the adult cells (0.64 +/- 0.30 vs. 0.54 +/- 0.27 s-1, respectively), but preterm cells shortened more than adult cells (68 +/- 12 vs. 55 +/- 11% of starting length, respectively; P < 0.05). The preparative and analytic methods described here are widely applicable to other smooth muscles and will allow contraction to be studied quantitatively at the single-cell level.

Refilling of caffeine-sensitive intracellular calcium stores in bovine airway smooth muscle cells

The goal of this study was to assess the mechanisms by which the caffeine-sensitive calcium stores of airway smooth muscle cells are refilled. Bovine trachealis cells were loaded with fura 2-AM (0.5 microM) for imaging of cytosolic calcium concentrations ([Ca2+]i) in the inner cytosol. After a first stimulation (S1) with caffeine, the response to a second stimulation (S2) depended on the presence of extracellular calcium during an intervening 80-s-long refilling phase. The S2-to-S1 ratio (S2/S1) was 0.11 +/- 0.05 (n = 13 cells) during calcium-free refilling but 0.72 +/- 0.04 (n = 36 cells) within 80 s of exposure to extracellular calcium. Maximum mean [Ca2+]i during the 80 s of refilling was not different for calcium-free (116 +/- 19 nM; n = 13 cells) versus extracellular calcium plus nickel (2 mM) (121 +/- 12 nM; n = 21 cells); despite this, significantly greater refilling (S2/S1 0.58 +/- 0.06; n = 24 cells) occurred in the presence of extracellular calcium plus nickel. The protein tyrosine kinase inhibitors genistein (100 microM) and ST-638 (50 microM) significantly decreased refilling over 80 s (S2/S1 0.35 +/- 0.06, n = 14 cells and 0.51 +/- 0.07, n = 14 cells, respectively). Daidzein (100 microM) had no effect on S2/S1. We concluded that [Ca2+]i of the inner cytosol during refilling correlated poorly with S2/S1 values and that, therefore, additional compartments not well detected by fura 2 contribute to refilling. The findings suggest that calcium influx for refilling is segregated from the inner cytosol of the cell, relatively insensitive to nickel, and regulated or modulated by protein tyrosine kinase activity.

Cytokine-induced anorexia. Behavioral, cellular, and molecular mechanisms

Cytokines induce anorexia. Recent issues concerning mechanistic aspects are: (1) Cytokines induce anorexia through different modes of behavioral action, that is, by affecting meal size, meal duration, and meal frequency differentially. Profiles also depend on the concentration or dosage. (2) The interface between the periphery and brain. Specific cytokines may be transported from the periphery to the brain. Cytokines generate mediators that can act on peripheral and/or brain target sites. Cerebrovasculature endothelium can also generate signals to modulate neural activities. Evidence indicates that the proposed vagal afferent signaling requires reassessment. Because of paracrine and autocrine actions, local cytokine production within the brain can induce anorexia. (3) Cytokines act directly on hypothalamic neurons proposed to participate in feeding. (4) Cytokine<-->cytokine and cytokine<-->peptide/neurotransmitter interactions are critical; for example, cytokines interact to induce anorexia synergistically, neuropeptide Y<-->cytokine interactions are antagonist, and cytokine<-->neurotransmitter and cytokine<-->leptin<-->neuropeptide Y<-->CRH-glucocorticoid and other endocrine interactions are important. A leptin receptor is related to gp 130, a signal transducer among interleukin (IL)-6 subfamily receptors; gp 130 and related molecules may be an interface for feeding control in health and disease. Various cytokines upregulate leptin and gp 130. An integrative approach combining computerized meal pattern analyses with cellular and molecular approaches is being used to characterize mechanisms (ligands, receptors, transducing molecules, and intracellular mediators) involved in cytokine-induced anorexia.

Ionic mechanisms underlying electrical slow waves in canine airway smooth muscle

In canine bronchial smooth muscle (BSM), spasmogens evoke oscillations in membrane potential ("slow waves"). The depolarizing phase of the slow waves is mediated by voltage-dependent Ca2+ channels; we examined the roles played by Cl- and K+ currents and Na+-K+-ATPase activity in mediating the repolarizing phase. Slow waves were evoked using tetraethylammonium (25 mM) in the presence or absence of niflumic acid (100 microM; Cl- channel blocker) or ouabain (10 microM; block Na+-K+-ATPase) or after elevating external K+ concentration ([K+]) to 36 mM (to block K+ currents); curve fitting was performed to quantitate the rates of rise/fall and frequency under these conditions. Slow waves were markedly slowed, and eventually abolished, by niflumic acid but were unaffected by ouabain or high [K+]. Electrically evoked slow waves were also blocked in similar fashion by niflumic acid. We conclude that the repolarization phase is mediated by Ca2+-dependent Cl- currents. This information, together with our earlier finding that the depolarizing phase is due to voltage-dependent Ca2+ current, suggests that slow waves in canine BSM involve alternating opening and closing of Ca2+ and Cl- channels.

Physiological features of visceral smooth muscle cells, with special reference to receptors and ion channels

Visceral smooth muscle cells (VSMC) play an essential role, through changes in their contraction-relaxation cycle, in the maintenance of homeostasis in biological systems. The features of these cells differ markedly by tissue and by species; moreover, there are often regional differences within a given tissue. The biophysical features used to investigate ion channels in VSMC have progressed from the original extracellular recording methods (large electrode, single or double sucrose gap methods), to the intracellular (microelectrode) recording method, and then to methods for recording from membrane fractions (patch-clamp, including cell-attached patch-clamp, methods). Remarkable advances are now being made thanks to the application of these more modern biophysical procedures and to the development of techniques in molecular biology. Even so, we still have much to learn about the physiological features of these channels and about their contribution to the activity of both cell and tissue. In this review, we take a detailed look at ion channels in VSMC and at receptor-operated ion channels in particular; we look at their interaction with the contraction-relaxation cycle in individual VSMC and especially at the way in which their activity is related to Ca2+ movements and Ca2+ homeostasis in the cell. In sections II and III, we discuss research findings mainly derived from the use of the microelectrode, although we also introduce work done using the patch-clamp procedure. These sections cover work on the electrical activity of VSMC membranes (sect. II) and on neuromuscular transmission (sect. III). In sections IV and V, we discuss work done, using the patch-clamp procedure, on individual ion channels (Na+, Ca2+, K+, and Cl-; sect. IV) and on various types of receptor-operated ion channels (with or without coupled GTP-binding proteins and voltage dependent and independent; sect. V). In sect. VI, we look at work done on the role of Ca2+ in VSMC using the patch-clamp procedure, biochemical procedures, measurements of Ca2+ transients, and Ca2+ sensitivity of contractile proteins of VSMC. We discuss the way in which Ca2+ mobilization occurs after membrane activation (Ca2+ influx and efflux through the surface membrane, Ca2+ release from and uptake into the sarcoplasmic reticulum, and dynamic changes in Ca2+ within the cytosol). In this article, we make only limited reference to vascular smooth muscle research, since we reviewed the features of ion channels in vascular tissues only recently.

Activation of Ca(2+)-activated K+ (maxi-K+) channel by angiotensin II in myocytes of the guinea pig ileum

We investigated the regulation of the Ca(2+)-activated K+ (maxi-K+) channel by angiotensin II (ANG II) and its synthetic analog, [Lys2]ANG II, in freshly dispersed intestinal myocytes. We identified a maxi-K+ channel population in the inside-out patch configuration on the basis of its conductance (257 +/- 4 pS in symmetrical 150 mM KCl solution), voltage and Ca2+ dependence of channel opening, low Na(+)-to-K+ and Cl(-)-to-K+ permeability ratios, and blockade by external Cs+ and tetraethylammonium chloride. ANG II and [Lys2]ANG II caused an indirect, reversible, Ca(2+)- and dose-dependent activation of maxi-K+ channels in cell-attached experiments when cells were bathed in high-K+ solution. This effect was reversibly blocked by DUP-753, being that it is mediated by the AT1 receptor. Evidences that activation of the maxi-K+ channel by ANG II requires a rise in intracellular Ca2+ concentration ([Ca2+]i) as an intermediate step were the shift of the open probability of the channel-membrane potential relationship to less positive membrane potentials and the sustained increase in [Ca2+]i in fura 2-loaded myocytes. The preservation of the pharmacomechanical coupling of ANG II in these cells provides a good model for the study of transmembrane signaling responses to ANG II and analogs in this tissue.

Depression, stress and immunological activation: the role of cytokines in depressive disorders

Traditionally, both stress and depression have been associated with impaired immune function and increased susceptibility to infectious and neoplastic disease. However over the last number of years a large body of evidence suggests that major depression is associated with signs of immunological activation. Moreover it has been suggested that cytokine hypersecretion may be involved in the aetiology of depressive disorders. The present article reviews the evidence from both clinical and experimental studies which implicates immunological activation and particularly hypersecretion of cytokines in the onset and maintenance of depressive illness. Both clinical and experimental studies indicate that stress and depression are associated with increased circulating concentrations of cytokines such as IL-1beta, IL-6 and gamma-IFN and positive acute phase proteins, and hyperactivity of the HPA-axis. In addition, it has been reported that immunological activation induces "stress-like" behavioural and neurochemical changes in laboratory animals. Although for many years it has been suggested that stress acts a predisposing factor to depressive illness, the precise mechanisms by which stress-induced depressive symptoms occur are not fully understood. Nevertheless, behavioural changes due to stress have often been explained in terms of changes in neurotransmitter function in the brain. In the present article increased cytokine secretion is implicated as a mechanism whereby stress can induce depression.

Regulation of intracellular calcium in human esophageal smooth muscles

We have investigated sources of Ca2+ contributing to excitation of human esophageal smooth muscle, using fura 2 to study cytosolic free Ca2+ concentration ([Ca2+]i) in dispersed cells and contraction of intact muscles. Acetylcholine (ACh) caused an initial peak rise of [Ca2+]i followed by a plateau accompanied by reversible contraction. Removal of extracellular Ca2+ or addition of dihydropyridine Ca2+ channel blockers reduced the plateau phase but did not prevent contraction. Caffeine also caused elevation of [Ca2+]i and blocked responses to ACh. Undershoots of [Ca2+]i were apparent after ACh or caffeine. Blockade of the sarcoplasmic reticular Ca(2+)-ATPase by cyclopiazonic acid (CPA) reduced the ACh-evoked increase of [Ca2+]i and abolished the undershoot, indicating involvement of Ca2+ stores. When contraction was studied in intact muscles, removal of Ca2+ or addition of nifedipine reduced, but did not abolish, carbachol (CCh)-induced contraction. Elevation of extracellular K+ caused contraction that was inhibited by nifedipine, although CCh still elicited contraction. CPA caused contraction and suppressed the CCh-induced contraction, whereas ryanodine reduced CCh-induced contraction. Our studies provide evidence that muscarinic excitation of human esophagus involves both release of Ca2+ from intracellular stores and influx of Ca2+.

Actions of 4-chloro-3-ethyl phenol on internal Ca2+ stores in vascular smooth muscle and endothelial cells

1. Recently, 4-chloro-3-ethyl phenol (CEP) has been shown to cause the release of internally stored Ca2+ apparently through ryanodine-sensitive Ca2+ channels, in fractionated skeletal muscle terminal cisternae and in a variety of non-excitable cell types. Its action on smooth muscle is unknown. In this study, we characterized the actions of CEP on vascular contraction in endothelium-denuded dog mesenteric artery. We also determined its ability to release Ca2+, by use of Ca2+ imaging techniques, on dog isolated mesenteric artery smooth muscle cells and on bovine cultured pulmonary artery endothelial cells. 2. After phenylephrine-(PE, 10 microM) sensitive Ca2+ stores were depleted by maximal PE stimulation in Ca2+-free medium, the action of CEP on refilling of the emptied PE stores was tested, by first pre-incubating the endothelium-denuded artery in CEP for 15 min before Ca2+ was restored for a 30 min refilling period. At the end of this period, Ca2+ and CEP were removed, and the arterial ring was tested again with PE to assess the degree of refilling of the internal Ca2+ store. 3. In a concentration-dependent manner (30, 100 and 300 microM), CEP significantly reduced the size of the post-refilling PE contraction (49.4, 28.9 and 5.7% of control, respectively) in Ca2+-free media. This suggests that Ca2+ levels are reduced in the internal stores by CEP treatment. CEP alone did not cause any contraction either in Ca2+-containing or Ca2+-free Krebs solution. 4. Restoring Ca2+ in the presence of PE caused a large contraction, which reflects PE-induced influx of extracellular Ca2+. The contraction of tissues pretreated with 300 microM CEP was significantly less compared with controls. However, tissues pretreated with 30 and 100 microM CEP were unaffected. Washout of CEP over 30 min produced complete recovery of responses to PE in Ca2+-free and Ca2+-containing medium suggesting a rapid reversal of CEP effects. 5. Concentration-response curves were constructed for PE, 5-hydroxytryptamine (5-HT) and K+ in the absence of and after 30 min pre-incubation with 30, 100 and 300 microM CEP. In all cases, CEP caused a concentration-dependent depression of the maximum response to PE (84.8, 43.4 and 11.6% of control), 5-HT (65.4, 25.7 and 6.9% of control) and K+ (77.6, 41.1 and 10.8% of control). 6. Some arterial rings were pre-incubated with ryanodine (30 microM) for 30 min before the construction of PE concentration-response curves. In Ca2+-free Krebs solution, ryanodine alone did not cause any contraction. However, 58% (11 out of 19) of the tissues tested with ryanodine developed contraction (6.9+/-1.2% of 100 mM K+ contraction, n=11) in the presence of external Ca2+. EC50 values for PE in ryanodine-treated tissues (1.7+/-0.25 microM, n=16) were not significantly different from controls (2.5+/-0.41 microM, n=22). Maximum contractions to PE (118.5+/-4.4% of 100 mM K+ contraction, n=16) were also unaffected by ryanodine when compared to controls (129+/-4.2%, n=23). 7. When fura-2 loaded smooth muscle cells (n=13) and endothelial cells (n=27) were imaged for Ca2+ distribution, it was observed that 100 and 300 microM CEP in Ca2+-free medium caused Ca2+ release in both cell types. Smooth muscle cells showed a small decrease in cell length. Addition of EGTA (5 mM) reversed the effect of CEP on intracellular Ca2+ to control values. 8. These data show, for the first time in vascular smooth muscle and endothelial cells, that CEP releases Ca2+ more rapidly than ryanodine. Unlike ryanodine, CEP caused no basal contraction but depressed contractions to PE, 5-HT and K+. The lack of basal contraction may result from altered responsiveness of the contractile system to intracellular Ca2+ elevation.

Cellular mechanisms underlying carbachol-induced oscillations of calcium-dependent membrane current in smooth muscle cells from mouse anococcygeus

1. At a holding potential of -40 mV, carbachol (50 microM) produced a complex pattern of inward currents in single smooth muscle cells freshly isolated from the mouse anococcygeus. Membrane currents were monitored by the whole-cell configuration of the patch-clamp technique. Previous work has identified the first, transient component as a calcium-activated chloride current (ICl(Ca)) and the second sustained component as a store depletion-operated non-selective cation current (I(DOC)). The object of the present study was to examine the cellular mechanisms underlying the third component, a series of inward current oscillations (I(oscil)) superimposed on I(DOC). 2. Carbachol-induced I(oscil) (amplitude 97 +/- 11 pA; frequency 0.26 +/- 0.02 Hz) was inhibited by the chloride channel blocker anthracene-9-carboxylic acid (A-9-C; 1 mM), and by inclusion of 1 mM EGTA in the patch-pipette filling solution. 3. In calcium-free extracellular medium (plus 1 mM EGTA), carbachol produced an initial burst of oscillatory current which lasted 94 s before decaying to zero; I(oscil) could be restored by re-admission of calcium. The frequency, but not the amplitude, of I(oscil) increased with increasing concentrations of extracellular calcium (0.5-10 mM). 4. Inclusion of the inositol triphosphate (IP3) receptor antagonist heparin (5 mg ml(-1) in the patch-pipette filling solution, or pretreatment of cells with the sarcoplasmic reticulum (SR) calcium ATPase inhibitor cyclopiazonic acid (CPA; 10 microM), prevented the activation of I(oscil) by carbachol. Caffeine (10 mM) activated both ICl(Ca) and I(DOC) and prevented the induction of I(oscil) by carbachol. Caffeine and CPA also abolished I(oscil) in the presence of carbachol, as did both a low (3 microM) and a high (30 microM) concentration of ryanodine. 5. Carbachol-induced I(oscil) was abolished by the general calcium entry blocker SKF 96365 (10 MM) and by Cd2+ (100 microM), but was unaffected by La3+ (400 microM). As found previously, I(DOC) was also blocked by SKF 96365 and Cd2+, but not La3+; the inhibition of I(DOC) preceded the abolition of I(oscil) by 27 s with SKF 96365 and by 30 s with Cd2+. Nifedipine (1 microM) produced a partial inhibition of the carbachol-induced I(oscil) frequency at holding potentials of -20 mV and -60 mV and, in addition, reduced I(DOC) at -60 mV by 18%. 6. It is concluded that carbachol-induced inward current oscillations in mouse anococcygeus cells are due to a calcium-activated chloride current, and reflect oscillatory changes in cytoplasmic calcium ion concentration. These calcium oscillations are derived primarily from the SR stores, but entry of calcium into the cell is necessary for store replenishment and maintenance of the oscillations. Capacitative calcium entry (via I(DOC) appears to be important not only for sustained contraction of this tissue, but also as a route for re-filling of the SR and, therefore, represents an important target for the development of novel and selective drugs.

Na+/K+ ATPase mediates rhythmic spontaneous relaxations in canine airway smooth muscle

In canine airway smooth muscle, cyclopiazonic acid (CPA; selective blocker of the sarcoplasmic reticulum Ca(2+)-pump) evokes a contractile response which is initially mediated via release of internally sequestered Ca2+, but is later supported almost exclusively by electromechanical coupling. As such, this second component is highly sensitive to inhibition of voltage-dependent Ca(2+)-influx (e.g. dihydropyridines, removal of external Ca2+) or to membrane hyperpolarization. In the present study, we describe relaxations which occur spontaneously during this second component of the CPA-evoked contraction. These relaxations are also electromechanically mediated, since they are abolished by depolarization of the membrane by high-K+ media. TEA has relatively little effect on the phasic activity, thus ruling out an involvement of Ca(2+)-dependent K+ channels. On the other hand, the phasic activity is abolished by ouabain, by removal of external K+, or by cooling and is markedly slowed by removal of external Na+. These observations indicate that the phasic activity is mediated by the Na+/K(+)-ATPase.

Induction of hippocampal long-term depression requires release of Ca2+ from separate presynaptic and postsynaptic intracellular stores

Studies have suggested that an increase in intracellular [Ca2+] is necessary for the induction of both long-term potentiation (LTP) and long-term depression (LTD) of synaptic transmission, and that release of Ca2+ from intracellular storage pools can be necessary to induce LTP. We investigated whether release of Ca2+ from intracellular stores also is required for the induction of LTD at Schaffer collateral-CA1 synapses in hippocampal slices. Both thapsigargin (1 microM) and cyclopiazonic acid (1 microM), compounds that deplete all intracellular Ca2+ pools by blocking LTP-dependent Ca2+ uptake into intracellular compartments, blocked the induction, but not maintenance, of LTD by low-frequency stimulation (LFS) (1 Hz/15 min) without affecting baseline synaptic transmission. Washout of the reversible inhibitor cyclopiazonic acid restored the ability to induce LTD. In contrast, thapsigargin did not block depotentiation of LTP by 1 Hz LFS, suggesting that LTP causes a reduction in the threshold [Ca2+] necessary for LTD. Selective depletion of the ryanodine receptor-gated Ca2+ pool by bath application of ryanodine (10 microM) also blocked the induction of LTD, indicating a requirement for Ca(2+)-induced Ca2+ release. Impalement of CA1 pyramidal neurons with microelectrodes containing thapsigargin (500 nM to 200 microM) prevented the induction of LTD at synapses on that neuron without blocking LTD in the rest of the slice. In contrast, similar filling of CA1 pyramidal neurons with ryanodine (2 microM to 5 mM) did not block the induction of LTD. From these data, we conclude that the induction of LTD requires release of Ca2+ both from a presynaptic ryanodine-sensitive pool and from postsynaptic (presumably IP3-gated) stores.

Probing excitation-contraction coupling in trachealis smooth muscle with the mycotoxin cyclopiazonic acid

1. Muscarinic stimulation-induced tonic contraction of airway smooth muscle is independent of membrane potential. This contraction is not sensitive to inhibition by voltage-operated Ca2+ channel blockers or by K+ channel openers. 2. Cyclopiazonic acid (CPA) inhibits Ca2+ loading of internal stores but does not affect maximal tonic contraction induced by acetylcholine (ACh) in steady state conditions. 3. After depletion of internal Ca2+ stores with CPA, ACh-induced tonic contraction becomes dependent upon values of membrane potential. The contraction is then sensitive to voltage-operated Ca2+ channel blockers and to K+ channel openers. 4. Treatment of trachealis muscle with CPA potentiates the M2-mediated component of ACh stimulation, but this potentiation is not entirely responsible for the switch in excitation-contraction (E-C) coupling. 5. It is proposed that depletion of internal Ca2+ stores with CPA and promotion of M2-stimulation can lead to a switch in E-C coupling in trachealis smooth muscle from pharmaco- to electromechanical mode, perhaps by targeting a plasma membrane K+ channel.