Ca2+-images of smooth muscle cells and endothelial cells in one confocal plane in femoral artery segments of the rat

Downregulated caveolin-1 expression serves a potential role in coronary artery spasm by inducing nitric oxide production in vitro

The present study aimed to investigate the effects of downregulated caveolin-1 (Cav-1) expression on nitric oxide (NO) production in lipopolysaccharide (LPS)-damaged primary human umbilical vein endothelial cells (HUVECs) in a model of coronary artery spasm (CAS) microenvironment induced by acetylcholine (ACh) treatment. Small interfering RNA (siRNA)-mediated Cav-1 downregulation in HUVECs was confirmed by western blotting. The cell viability and superoxide dismutase (SOD) inhibition in HUVECs incubated with LPS (0, 10, 25, 50, 75 and 100 µg/ml) were measured by cell counting kit-8 assay and a SOD kit, respectively. Intracellular Ca2+ [(Ca2+)i] in Fluo4-acetoxymethyl ester-loaded cells was detected by fluorescence microscopy. NO levels in the cell culture supernatants were measured by the nitrate reductase method. The results indicated that transfection with Cav-1 siRNA, in particular siCav-1 (2), downregulated the Cav-1 protein expression. LPS at a dose of 75 µg/ml induced a significant decrease in HUVECs/si-NC and HUVECs/siCav-1 viability compared with the other concentrations of LPS. Compared with the effects of untreated cells, SOD inhibition in HUVECs/si-NC and HUVECs/siCav-1 was significantly decreased by LPS (75 µg/ml). In addition, ACh stimulation caused a greater increase in [Ca2+]i in HUVECs/si-NC as compared with LPS-treated HUVECs/si-NC. ACh stimulation also induced significantly higher NO levels in LPS-treated HUVECs/siCav-1 compared with LPS-treated HUVECs/si-NC cells (P<0.05). In conclusion, the downregulated Cav-1 expression served a key role in NO production in the in vitro model of CAS induced by ACh stimulation of LPS-damaged HUVECs.

Overactive bladder mediated by accelerated Ca2+ influx mode of Na+/Ca2+ exchanger in smooth muscle

The Na(+)/Ca(2+) exchanger (NCX) is thought to be a key molecule in the regulation of cytosolic Ca(2+) dynamics. The relative importance of the two Ca(2+) transport modes of NCX activity leading to Ca(2+) efflux (forward) and influx (reverse) in smooth muscle, however, remains unclear. Unexpectedly, spontaneous contractions of urinary bladder smooth muscle (UBSM) were enhanced in transgenic mice overexpressing NCX1.3 (NCX1.3(tg/tg)). The enhanced activity was attenuated by KB-R7943 or SN-6. Whole cell outward NCX current sensitive to KB-R7943 or Ni(2+) was readily detected in UBSM cells from NCX1.3(tg/tg) but not wild-type mice. Spontaneous Ca(2+) transients in myocytes of NCX1.3(tg/tg) were larger and frequently resulted in propagating events and global elevations in cytosolic Ca(2+) concentration. Significantly, NCX1.3(tg/tg) mice exhibited a pattern of more frequent urination of smaller volumes and this phenotype was reversed by oral administration of KB-R7943. On the other hand, KB-R7943 did not improve it in KB-R7943-insensitive (G833C-)NCX1.3(tg/tg) mice. We conclude that NCX1.3 overexpression is associated with abnormal urination owing to enhanced Ca(2+) influx via reverse mode NCX leading to prolonged, propagating spontaneous Ca(2+) release events and a potentiation of spontaneous UBSM contraction. These findings suggest the possibility that NCX is a candidate molecular target for overactive bladder therapy.

Screening quality for Ca2+-activated potassium channel in IonWorks Quattro is greatly improved by using BAPTA-AM and ionomycin

INTRODUCTION

IonWorks automated patch clamp systems are being widely used for ion channel drug discovery, but the perforated patch mode of these systems makes it difficult to obtain a steady intracellular Ca(2+) concentration ([Ca(2+)](i)). This difficulty prevents obtaining high-quality data regarding Ca(2+)-activated channels such as BK and SK channels. We examined the methods for stabilizing [Ca(2+)](i) in the IonWorks Quattro automated patch clamp system to evaluate BK channels.

METHODS

Electrophysiological recordings were performed using the single-hole or population patch clamp mode of IonWorks Quattro. To increase [Ca(2+)](i), ionomycin was used. The variation in the BK current and the effect of BK channel modulators were examined in the presence and absence of an intracellular Ca(2+) chelator, BAPTA-AM (20μM).

RESULTS

BK current activated by step pulses to +100mV in the presence of ionomycin exhibited large variation (ranging from 0.086 to 11nA). In individual cells, oscillation of the current amplitude was observed when five repetitive pulses were applied at 0.1Hz. Approximately 30% of cells exhibited current variation exceeding 20% when the variation was calculated using the first and third pulses. However, BAPTA-AM treatment before current measurement decreased the number of cells displaying large variation (>20%) to 5%. In the presence of BAPTA-AM, the BK channel modulators NS1619 and 12,14-dichlorodehydroabietic acid increased the BK current at concentrations of 10μM or more showing clear concentration dependency, whereas in its absence, the effect of both compounds was detected only at 30μM.

DISCUSSION

The main finding of this study is that the [Ca(2+)](i) variation in the basal condition is very large and hinders the accurate evaluation of compounds in Ca(2+)-activated ion channels. The application of BAPTA-AM and ionomycin greatly improved the precision of BK channel screening, and this method should be applicable to other Ca(2+)-activated ion channels such as SK channels.

Calcium and electrical signalling along endothelium of the resistance vasculature

This MiniReview is focused on the nature of intercellular signalling along the endothelium that helps to co-ordinate blood flow control in vascular resistance networks. Vasodilation initiated by contracting skeletal muscle ascends from arterioles within the tissue to encompass resistance arteries upstream and thereby increase blood flow during exercise. In resistance vessels, acetylcholine microiontophoresis or intracellular current injection initiates hyperpolarization that conducts through gap junction channels (GJCs) along the vessel wall resulting in conducted vasodilation (CVD). Both ascending vasodilation and CVD are eliminated with endothelial cell (EC) disruption, pointing to common signalling events and mutual dependence upon EC integrity. As demonstrated by electrical coupling and dye transfer during intracellular recording, their longitudinal orientation and robust expression of GJCs enable ECs to play a predominant role in CVD. Once conduction is initiated, a major interest centres on whether CVD is purely passive or involves additional 'active' signalling events. Here, we discuss components for Ca²⁺ and electrical signalling with an emphasis on intercellular coupling through endothelial GJCs. We stress the importance of understanding relationships between intracellular Ca²⁺ dynamics, EC hyperpolarization and CVD while integrating findings from isolated ECs into more complex interactions in vivo. Whereas endothelial dysfunction accompanies cardiovascular disease and the components of intra- and inter-cellular signalling are increasingly well defined, little is known of how Ca²⁺ signalling and electrical conduction along microvascular endothelium are altered in diseased states. Thus, greater insight into how these relationships are governed and interact is a key goal for continued research efforts.

Endothelial mitochondria and heart disease

The endothelium is vital to the proper functioning in the heart, in particular due to its production of nitric oxide (NO) which regulates vascular tone. Damage to the endothelium contributes to the development of atherosclerosis, and hence to possible myocardial infarction and subsequent heart failure. Like most cells, endothelial cells contain mitochondria, despite their having relatively little dependence on oxidative phosphorylation for ATP production. However, endothelial mitochondria are centrally involved in maintaining the fine regulatory balance between mitochondrial calcium concentration, reactive oxygen species (ROS) production, and NO. This raises the question of whether damage to endothelial mitochondria would have repercussions in terms of the development of heart disease. In fact, increasingly nuanced techniques enabling restricted transgenic expression of antioxidant proteins in mice has demonstrated that mitochondrial ROS do contribute to endothelial damage. New pharmaceutical approaches designed to target protective molecules such as ROS scavengers to the mitochondria promise to be effective in preventing heart disease. As well as protecting cardiomyocytes, these drugs may have the added benefit of preventing damage to the endothelial mitochondria. However, much remains to be done in understanding the contribution that mitochondria make to endothelial function.

How Structure, Ca Signals, and Cellular Communications Underlie Function in Precapillary Arterioles

Rationale : Precapillary arterioles control blood flow to tissues and their correct function is vital. However, their small size has limited study and little is known concerning the calcium signals in their endothelial and muscle cells and how these relate to function.

Objective : We aimed to investigate whether these small vessels are specialized in terms of structure and calcium signaling.

Methods and Results : Using in situ confocal imaging we have studied the ultrastructure, Ca signaling and coordination of contraction in precapillary arterioles in ureter and vas deferens. We have compared the data to that from a small mesenteric artery. In the precapillary arteriole, 1 myocyte covers a ≈10-μm length, and contraction of this single cell can decrease the diameter of this segment. In the mesenteric artery, more than 20 myocytes are required for this. In the precapillary arteriole, Ca signals arise solely from Ca release from the sarcoplasmic reticulum through inositol 1,4,5-trisphosphate-induced Ca release and not via ryanodine receptors. Agonist-induced Ca signals do not require Ca entry into the cell, do not spread or synchronize with neighboring cells, and are unaffected by endothelial stimulation, thereby allowing local control. This contrasts with the mesenteric artery, where Ca entry and ryanodine receptors are important and stimulation of the endothelium inhibits myocyte Ca signals and contraction.

Conclusions : These data reveal the structural and signaling specializations underlying how blood flow is locally regulated, provide new insight into control of microcirculation, and provide a framework to explain its vulnerability to disease.

Vasodilator efficacy of nitric oxide depends on mechanisms of intracellular calcium mobilization in mouse aortic smooth muscle cells

BACKGROUND AND PURPOSE

Reduction of intracellular calcium ([Ca(2+)](i)) in smooth muscle cells (SMCs) is an important mechanism by which nitric oxide (NO) dilates blood vessels. We investigated whether modes of Ca(2+) mobilization during SMC contraction influenced NO efficacy.

EXPERIMENTAL APPROACH

Isometric contractions by depolarization (high potassium, K(+)) or alpha-adrenoceptor stimulation (phenylephrine), and relaxations by acetylcholine chloride (ACh), diethylamine NONOate (DEANO) and glyceryl trinitrate (GTN) and SMC [Ca(2+)](i) (Fura-2) were measured in aortic segments from C57Bl6 mice.

KEY RESULTS

Phenylephrine-constricted segments were more sensitive to endothelium-derived (ACh) or exogenous (DEANO, GTN) NO than segments contracted by high K(+) solutions. The greater sensitivity of phenylephrine-stimulated segments was independent of the amount of pre-contraction, the source of NO or the resting potential of SMCs. It coincided with a significant decrease of [Ca(2+)](i), which was suppressed by sarcoplasmic reticulum (SR) Ca(2+) ATPase (SERCA) inhibition, but not by soluble guanylyl cylase (sGC) inhibition. Relaxation of K(+)-stimulated segments did not parallel a decline of [Ca(2+)](i). However, stimulation (BAY K8644) of L-type Ca(2+) influx diminished, while inhibition (nifedipine, 1-100 nM) augmented the relaxing capacity of NO.

CONCLUSIONS AND IMPLICATIONS

In mouse aorta, NO induced relaxation via two pathways. One mechanism involved a non-cGMP-dependent stimulation of SERCA, causing Ca(2+) re-uptake into the SR and was prominent when intracellular Ca(2+) was mobilized. The other involved sGC-stimulated cGMP formation, causing relaxation without changing [Ca(2+)](i), presumably by desensitizing the contractile apparatus. This pathway seems related to L-type Ca(2+) influx, and L-type Ca(2+) channel blockers increase the vasodilator efficacy of NO.

Relaxation induced by calcium ionophore is impaired in carotid arteries from 2K-1C rats due to failed effect of nitric oxide on the smooth muscle cells

Vascular endothelium generates nitric oxide (NO) in large vessels and induces relaxation of vascular smooth muscle cells (VSMC). The aim of this study was to evaluate the contribution of NO produced in the endothelial cells (EC) to the relaxation induced by the Ca2+ ionophore A23187 and whether this relaxation is impaired in renal hypertensive (2K-1C) rat arteries. Concentration-effect curves for A23187 were constructed in intact endothelium isolated carotid rings from 2K-1C and normotensive (2K) in the absence or in the presence of the extracellular NO scavenger haemoglobin or inhibitors of NO-synthase (NOS, L-NOARG), guanylyl-cyclase (GC, ODQ). In carotid rings loaded with Fluo-3AM, both EC and VSMC were simultaneously imaged by a confocal microscope and [Ca2+]c was derived from fluorescence intensities (IF). The maximal relaxation (ME) induced by A23187 was lower in 2K-1C than in 2K arteries. A23187-induced relaxation was abolished by haemoglobin and L-NOARG in both groups. ODQ reduced the ME to A23187 in 2K and abolished its relaxation in 2K-1C. A23187 increased [Ca2+]c in a similar way in 2K and 2K-1C EC, and decreased [Ca2+]c in VSMC, which effect was higher in 2K than in 2K-1C arteries. L-NOARG inhibited the effect of A23187 in VSMC from 2K and abolished it in 2K-1C rats. On the other hand, L-NOARG did not modify the effect of A23187 in EC from 2K and 2K-1C rats. The basal content of cGMP was higher in 2K than in 2K-1C arterial rings that was similarly increased by A23187. In conclusion, the Ca2+ ionophore A23187 increases Ca2+, activates NOS and NO production in the EC activating GC in VSMC and [Ca2+]c decrease. All these effects are higher in 2K, which contribute to the impaired relaxation to A23187 in 2K-1C rat arteries.

Oxidative stress and COX cause hyper-responsiveness in vascular smooth muscle of the femoral artery from diabetic rats

BACKGROUND AND PURPOSE

To investigate the dysfunction of vascular smooth muscle in streptozotocin-induced diabetic rats.

EXPERIMENTAL APPROACH

Rings without endothelium of femoral arteries were suspended in organ chambers for isometric tension recording. The production of oxygen-derived free radicals was measured with 2',7'-dichlorodihydrofluorescein diacetate using confocal microscopy. The protein expressions were measured by western blotting.

KEY RESULTS

The concentration-response curves to U46619 and phenylephrine, but not that to KCl, were shifted to the left, suggesting a hypersensitivity of cell membrane receptors in diabetes. Exogenous oxygen-derived free radicals induced greater vasoconstrictions in the femoral artery from diabetic rats. Chronic treatment with apocynin (inhibitor of NADPH oxidase) and acute exposure to MnTMPyP (SOD/catalase mimetic) normalized the response. The catalase activity and the total glutathione level were reduced in arteries from streptozotocin-treated rats, confirming a redox abnormality. The basal oxidative state was higher in arteries from streptozotocin-treated rats and reduced in arteries from apocynin- and streptozotocin-treated rats, suggesting that the functional changes in diabetes are due to a chronic increase in oxidative stress. In the arteries of streptozotocin-treated rats, inhibitors of COX-1 and/or COX-2 prevented the hypersensitivity and reduced the increase in oxidative stress caused by phenylephrine and U46619, suggesting that both isoforms contribute to the smooth muscle dysfunction. The expression of proteins for COX-1 and COX-2 was increased in arteries of streptozotocin-treated rats and reduced in preparations of apocynin- and streptozotocin-treated rats.

CONCLUSIONS AND IMPLICATIONS

Chronic diabetes and the resulting increased oxidative stress activate the production of COX-derived vasoconstrictor prostanoids causing hypersensitivity of vascular smooth muscle.

Antiphase oscillations of endothelium and smooth muscle [Ca2+]i in vasomotion of rat mesenteric small arteries

The mechanisms leading to vasomotion in the presence of noradrenaline and inhibitors of the sarcoplasmic/endoplasmic reticulum calcium ATPase were investigated in isolated rat mesenteric small arteries. Isobaric diameter and isometric force were measured together with membrane potential in endothelial cells and smooth muscle cells (SMC). Calcium in the endothelial cells and SMC was imaged with confocal microscopy. In the presence of noradrenaline and cyclopiazonic acid, ryanodine-insensitive oscillations in tone were produced. The frequency was about 1 min(-1) and amplitude about 70% of the maximal tone. The amplitude was reduced by indomethacin and increased with L-NAME. Vasomotion was inhibited by nifedipine and by 40 mM potassium. The frequency was increased and amplitude decreased by removal of the endothelium and by application of charybdotoxin and apamin. The vasomotion was associated with in-phase oscillations of membrane potential in endothelial cells and SMC and oscillations of [Ca2+]i that were in near anti-phase. We suggest a working model for the generation of oscillation based on a membrane oscillator where ion channels in both endothelial cells and SMC interact via a current running between the two cell types through myoendothelial gap junctions, which sets up a near anti-phase oscillation of [Ca2+]i in the two cell types.

Calcium oscillations induced by ATP in human umbilical cord smooth muscle cells

Arterial smooth muscle cells exhibit vasomotion, related to oscillations in intracellular Ca(2+) concentration, but the origin and function of these has not yet been fully determined. We measured intracellular Ca(2+) using conventional fluorescent methods in primary cultured, human umbilical cord artery smooth muscle cells (HUCASMC). Spontaneous oscillations in Ca(2+) was found in only 1% of all cells but exogenous, micromolar concentrations of ATP could induce Ca(2+) oscillations in 70% of cells with the most common pattern being one of regular amplitude and frequency with a return to basal levels between each peak. The P2Y agonist, UTP, but not the P2X agonist alphabeta-methylene ATP, could also induce Ca(2+) oscillations. Once induced, these oscillations could not be blocked by G-protein, PLC, VGCC or TRP channel antagonists applied individually, but could be prevented when antagonists were applied together. In the presence of EGTA, micromolar concentrations of ATP induced an elevation in intracellular Ca(2+) but did not induce Ca(2+) oscillations. The oscillation frequency induced by ATP was affected by bath Ca(2+) concentration. Taken together, these data suggest that external Ca(2+) entry maintains the Ca(2+) oscillation induced by activation of P2Y receptors. Once induced, multiple mechanisms are involved to maintain the oscillation and the oscillation frequency is determined by the speed of Ca(2+) refilling. Chronic hypoxia enhanced the Ca(2+) response and altered the oscillation frequency. We suggest that these oscillations may play a role in the maintenance of umbilical blood flow during situations in which GPCR are activated.

Endothelial function in aorta segments of apolipoprotein E-deficient mice before development of atherosclerotic lesions

Acetylcholine (ACh)-induced relaxation declines in apolipoprotein E-deficient (apoE-/-) mouse aortas, but only after atherosclerotic plaque formation. This study investigated intracellular calcium concentrations [Ca2+]i and changes in phenylephrine-induced contractions as index of baseline nitric oxide (NO) bioavailability before plaque development. Isometric contractions of thoracic aorta rings of young (4 months) apoE-/- and C57BL/6J (WT) mice were evoked by phenylephrine (3x10(-9)-3x10(-5) M) in the presence and absence of endothelial cells (ECs) or NO synthase (NOS) inhibitors. [Ca2+]i (Fura-2 AM) and endothelium-dependent relaxation were measured at baseline and after ACh stimulation. Segments of apoE-/- mice were significantly more sensitive and developed more tension than WT segments in response to phenylephrine. The differences disappeared after NOS inhibition or EC removal or upon increasing [Ca2+]i in apoE-/- strips with 10(-6) M cyclopiazonic acid or 10(-7) M Ca2+-ionophore A23187. Expression of endothelial NOS (eNOS) mRNA was similar in apoE-/- and WT aorta segments. Basal [Ca2+]i was significantly lower in apoE-/- than in WT strips. Relaxation by ACh (3x10(-9)-10(-5) M) was time- and dose-dependently related to [Ca2+]i, but neither ACh-induced relaxation nor Ca2+ mobilization were diminished in apoE-/- strips. In conclusion, basal, but not ACh-induced NO bioavailability, was compromised in lesion-free aorta of apoE-/- mice. Decreased basal NO bioavailability was not related to lower eNOS expression, but most likely related to lower basal [Ca2+]i. These findings further point to important differences between basal and stimulated eNOS activity.

Calcium mobilization and spontaneous transient outward current characteristics upon agonist activation of P2Y2 receptors in smooth muscle cells

A quantitative model is provided that links the process of metabotropic receptor activation and sequestration to the generation of inositol 1,4,5-trisphosphate, the subsequent release of calcium from the central sarcoplasmic reticulum, and the consequent release of calcium from subsarcolemma sarcoplasmic reticulum that acts on large-conductance potassium channels to generate spontaneous transient outward currents (STOCs). This model is applied to the case of STOC generation in vascular A7r5 smooth muscle cells that have been transfected with a chimera of the P2Y(2) metabotropic receptor and green fluorescent protein (P2Y(2)-GFP) and exposed to the P2Y(2) receptor agonist uridine 5'-triphosphate. The extent of P2Y(2)-GFP sequestration from the membrane on exposure to uridine 5'-triphosphate, the ensuing changes in cytosolic calcium concentration, as well as the interval between STOCs that are subsequently generated, are used to determine parameter values in the model. With these values, the model gives a good quantitative prediction of the dynamic changes in STOC amplitude observed upon activation of metabotropic P2Y(2) receptors in the vascular smooth muscle cell line.

Spreading dilatation in rat mesenteric arteries associated with calcium-independent endothelial cell hyperpolarization

Both ACh and levcromakalim evoke smooth muscle cell hyperpolarization and associated relaxation in rat mesenteric resistance arteries. We investigated if they could evoke conducted vasodilatation along isolated arteries, whether this reflected spreading hyperpolarization and the possible mechanism involved. Focal micropipette application of either ACh, to stimulate endothelial cell muscarinic receptors, or levcromakalim, to activate smooth muscle K(ATP) channels, each evoked a local dilatation (88 +/- 14%, n= 6 and 92 +/- 6% reversal of phenylephrine-induced tone, n= 11, respectively) that rapidly spread upstream (at 1.5 mm 46 +/- 19%, n= 6 and 57 +/- 13%, n= 9) to dilate the entire isolated artery. The local dilatation to ACh was associated with a rise in endothelial cell [Ca(2+)](i) (F/F(t = 0)= 1.22 +/- 0.33, n= 14) which did not spread beyond 0.5 mm (F/F(t = 0)= 1.01 +/- 0.01, n= 14), while the local dilatation to levcromakalim was not associated with any change in endothelial cell [Ca(2+)](i). In contrast, ACh and levcromakalim both stimulated local (12.7 +/- 1.2 mV, n= 10 and 13.5 +/- 4.7 mV, n= 10) and spreading (at 2 mm: 3.0 +/- 1.1 mV, n= 5 and 4.1 +/- 0.7 mV, n= 5) smooth muscle hyperpolarization. The spread of hyperpolarization could be prevented by cutting the artery, so was not due to a diffusible agent. Both the spreading dilatation and hyperpolarization were endothelium dependent. The injection of propidium iodide into either endothelial or smooth muscle cells revealed extensive dye coupling between the endothelial cells, but limited coupling between the smooth muscle cells. Some evidence for heterocellular spread of dye was also evident. Together, these data show that vasodilatation can spread over significant distances in mesenteric resistance arteries, and suggest this reflects an effective coupling between the endothelial cells to facilitate [Ca(2+)](i)-independent spread of hyperpolarization.

A novel action of palmitoyl-L-carnitine in human vascular endothelial cells

Palmitoyl-L-carnitine (palcar), which accumulates in ischemic heart, affects cellular functions of vascular endothelium in the ischemic area. The aim of this study was to examine the effects of palcar on intracellular Ca(2+) concentration ([Ca(2+)](i)) in vascular endothelial cells in comparison with those of sphingosine-1-phosphate (S1P) and to investigate the underlying mechanisms. Application of palcar at a concentration range between 0.3 and 3 micro M elevated [Ca(2+)](i) in huvecs, and its potency was about 30 times lower than that of S1P. When human umbilical vein endothelial cells (huvecs) were treated with 100 ng/ml pertussis toxin (PTX) for 15 h, they failed to respond to palcar or S1P, but did respond to 3 micro M histamine (His), suggesting that the response induced by palcar as well as S1P is mediated by a PTX-sensitive GTP binding protein, Gi. Although the sensitivity to palcar and S1P varied widely among huvecs from individuals, response to 3 micro M palcar in each huvec clearly paralleled that to 0.3 micro M S1P (r = 0.79, P<0.001). On the other hand, pre-treatment of huvecs with palcar abolished subsequent S1P-induced elevation of [Ca(2+)](i), but not the His-induced elevation. Our data indicate that palcar has a novel action on huvecs as a potential agonist of receptors for S1P. Effective inhibition of the response to S1P by palcar suggests that palcar affects functions regulated by S1P.

A new technique for simultaneous and in situ measurements of Ca2+ signals in arteriolar smooth muscle and endothelial cells

We report here the first local and global Ca(2+) measurements made from in situ terminal arterioles. The advantages of the method are that there is minimal disturbance to the vessels, which retain their relationship to the tissue they are supplying (rat ureter) and the small size of vessel that can be studied. Good loading with the Ca(2+) indicator, Fluo-4 was obtained, and confocal sectioning through the tissue enabled vascular smooth muscle and endothelial cells to be clearly seen, along with red blood cells, nerve endings and the ureteric smooth muscle cells. We find the terminal arterioles to be extremely active, both spontaneously and in response to nor-adrenaline stimulation, with Ca(2+) sparks occurring in the vascular myocytes and Ca(2+) puffs in the endothelial cells. Even under resting conditions, endothelial cells produced oscillations and waves, which could pass from cell to cell, whereas the vascular myocytes only produced waves in response to agonist stimulation, and with no increase in the frequency of Ca(2+) sparks, and no spread from cell to cell. We compare our data to those obtained in dissected intact vessels and single cells. We conclude that this approach is a convenient and useful method for studying inter- and intracellular Ca(2+) signalling events and communication between cell types, particularly in very small vessels.

Effects of KRN4884, a Novel K+ Channel Opener, on Ionic Currents in Rabbit Femoral Arterial Myocytes

Effects of KRN4884 (5-amino-N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine), a novel K(+) channel opener, on ionic currents were examined in rabbit femoral arterial myocytes (RFAMs). Under whole-cell clamp conditions where cells were superfused with 5.9 mM K(+) bathing solution, KRN4884 elicited an outward current at -30 mV. KRN4884-induced current had a reversal potential of -78 mV and was abolished by application of glibenclamide (glib). KRN4884 was approximately 43 times more potent than levcromakalim in activating an ATP-sensitive K(+) current (I(K-ATP)). On the other hand, KRN4884 affected neither voltage-dependent Ca(2+) nor delayed rectifier K(+) channel currents. In the inside-out patch clamp configuration where cells were superfused with the symmetrical 140 mM K(+) solution, KRN4884 activated 47 pS K(+) channels in the presence of adenosine diphosphate. Similar 47 pS K(+) channels, which were reversibly inhibited by glib, were recorded under outside-out patch conditions. Using RT-PCR analysis, we found that inward rectifier K channel 6.1 (Kir6.1) and sulfonylurea 2B (SUR2B) transcripts were predominantly expressed in rabbit femoral artery. These results indicate that KRN4884 potently activates I(K-ATP) in RFAMs. The KRN4884-sensitive 47 pS K(+) channel activity underlying I(K-ATP) is a vascular type K(ATP) channel consisting of Kir6.1 and SUR2B and has similar characteristics to those of ATP-sensitive K(+) channels activated by K(+) channel openers in other types of smooth muscles.