Neuroregulation by vasoactive intestinal peptide (VIP) of mucus secretion in ferret trachea: activation of BK(Ca) channels and inhibition of neurotransmitter release

Neural control of the lower airways: Role in cough and airway inflammatory disease

Airway function is under constant neurophysiological control, in order to maximize airflow and gas exchange and to protect the airways from aspiration, damage, and infection. There are multiple sensory nerve subtypes, whose disparate functions provide a wide array of sensory information into the CNS. Activation of these subtypes triggers specific reflexes, including cough and alterations in autonomic efferent control of airway smooth muscle, secretory cells, and vasculature. Importantly, every aspect of these reflex arcs can be impacted and altered by local inflammation caused by chronic lung disease such as asthma, bronchitis, and infections. Excessive and inappropriate activity in sensory and autonomic nerves within the airways is thought to contribute to the morbidity and symptoms associated with lung disease.

A Comparative Peptidomic Characterization of Cultured Skeletal Muscle Tissues Derived From db/db Mice

As an important secretory organ, skeletal muscle has drawn attention as a potential target tissue for type 2 diabetic mellitus (T2DM). Recent peptidomics approaches have been applied to identify secreted peptides with potential bioactive. However, comprehensive analysis of the secreted peptides from skeletal muscle tissues of db/db mice and elucidation of their possible roles in insulin resistance remains poorly characterized. Here, we adopted a label-free discovery using liquid chromatography tandem mass spectrometry (LC-MS/MS) technology and identified 63 peptides (42 up-regulated peptides and 21 down-regulated peptides) differentially secreted from cultured skeletal muscle tissues of db/db mice. Analysis of relative molecular mass (Mr), isoelectric point (pI) and distribution of Mr vs pI of differentially secreted peptides presented the general feature. Furthermore, Gene ontology (GO) and pathway analyses for the parent proteins made a comprehensive functional assessment of these differential peptides, indicating the enrichment in glycolysis/gluconeogenesis and striated muscle contraction processes. Intercellular location analysis pointed out most precursor proteins of peptides were cytoplasmic or cytoskeletal. Additionally, cleavage site analysis revealed that Lysine (N-terminal)-Alanine (C-terminal) and Lysine (N-terminal)-Leucine (C-terminal) represents the preferred cleavage sites for identified peptides and proceeding peptides respectively. Mapped to the precursors' sequences, most identified peptides were observed cleaved from creatine kinase m-type (KCRM) and fructose-bisphosphate aldolase A (Aldo A). Based on UniProt and Pfam database for specific domain structure or motif, 44 peptides out of total were positioned in the functional motif or domain from their parent proteins. Using C2C12 myotubes as cell model in vitro, we found several candidate peptides displayed promotive or inhibitory effects on insulin and mitochondrial-related pathways by an autocrine manner. Taken together, this study will encourage us to investigate the biologic functions and the potential regulatory mechanism of these secreted peptides from skeletal muscle tissues, thus representing a promising strategy to treat insulin resistance as well as the associated metabolic disorders.

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Role of parasympathetic nerves and muscarinic receptors in allergy and asthma

Parasympathetic nerves control the symptoms and inflammation of allergic diseases primarily by signaling through peripheral muscarinic receptors. Parasympathetic signaling targets classic effector tissues such as airway smooth muscle and secretory glands and mediates acute symptoms of allergic disease such as airway narrowing and increased mucus secretion. In addition, parasympathetic signaling modulates inflammatory cells and non-neuronal resident cell types such as fibroblasts and smooth muscle contributing to chronic allergic inflammation and tissue remodeling. Importantly, muscarinic antagonists are experiencing a rebirth for the treatment of asthma and may be useful for treating other allergic diseases.

Mucus secretion from individual submucosal glands of the ferret trachea

Mucus secretion from individual tracheal glands in adult ferrets was studied with time-lapse optical imaging of mucus droplets under an oil layer. Density of functional glands (determined by responses to 1 muM carbachol) was 1.5 +/- 0.3 per mm(2) (n = 6). Secretion rates (in pl.min(-1).gland(-1)) were as follows: 4.1 +/- 0.7 basal (unstimulated; n = 27, 669 glands), 338 +/- 70 to 10 microM forskolin (n = 8, 90 glands), 234 +/- 13 to 1 microM VIP (n = 6, 57 glands), 183 +/- 92 to 10 microM isoproterenol (n = 3, 33 glands), 978 +/- 145 to 1 microM carbachol (n = 11, 131 glands), and 1,348 +/- 325 to 10 muM phenylephrine (n = 7, 74 glands). The potency (EC(50), in microM) and efficacy (V(max), in pl x min(-1) x gland(-1)) were 7.6 (EC(50)) and 338 +/- 16 (V(max)) to forskolin, 1.0 (EC(50)) and 479 +/- 19 (V(max)) to VIP, 0.6 (EC(50)) and 1,817 +/- 268 (V(max)) to carbachol, and 3.7 (EC(50)) and 1,801 +/- 95 (V(max)) to phenylephrine. Although carbachol and phenylephrine were equally effective secretagogues, only carbachol caused contractions of the trachealis muscle. Synergy was demonstrated between 300 nM isoproterenol and 100 nM carbachol, which, when combined, produced a secretion rate almost fourfold greater than predicted from their additive effect. The dependence of fluid secretion on Cl(-) and HCO(3)(-) varied depending on the mode of stimulation. Secretion stimulated by VIP or forskolin was reduced by approximately 60% by blocking either anion, while carbachol-stimulated secretion was blocked 68% by bumetanide and only 32% by HEPES replacement of HCO(3)(-). These results provide parametric data for comparison with fluid secretion from glands in ferrets lacking CFTR.

Involvement of P2Y1 and P2Y11 purinoceptors in parasympathetic inhibition of colonic smooth muscle

Purinergic signaling was first recognized in the guinea pig (Cavia porcellus) taenia coli, where relaxation of smooth muscle by nerve-released ATP may involve the activation of P2Y(1) and P2Y(11) receptors, and where transcripts for both genes have been found. A partial sequence for P2Y(11) protein was identified; the full-length P2Y(1) sequence has already been described. P2Y(1) and P2Y(11) proteins were localized by immunohistochemistry in smooth muscle cells. P2X(2) and P2X(3) proteins were also localized in motoneurons of the myenteric plexus. alphabeta-Methylene-ATP (alphabetameATP) and dibenzoyl-ATP (BzATP) evoked fast relaxations in the taenia, and they were inhibited by the P2Y(1) receptor antagonist 2'-deoxy-N(6)-methyladenosine 3',5'-bisphosphate (MRS2179). However, alphabetameATP and BzATP may stimulate neuronal P2X receptors to release ATP, which then acts on P2Y(1) receptors. In accordance, fast relaxations evoked by alphabetameATP and BzATP were inhibited by the P2X(3) and P2X(2/3) receptor antagonist 5-({[3-phenoxybenzyl][(1S)-1,2,3,4-tetrahydro-1-naphthalenyl] amino} carbonyl)-1,2,4-benzene-tricarboxylic acid (A317491). When P2Y(1), P2X(3), and P2X(2/3) receptors were blocked and adenosine was removed enzymatically, alphabetameATP and BzATP evoked slow relaxations that were inhibited by Reactive Red. Fast and slow relaxations involve small and large conductance calcium-activated potassium channels; the latter are dependent on intracellular cyclic AMP levels, which altered the duration and amplitude of relaxations. alphabetameATP and BzATP were confirmed as agonists, and Reactive Red as an antagonist, of human P2Y(11) receptors. In summary, G(q)-coupled P2Y(1) receptors are involved mainly in fast relaxations, whereas G(q)and G(s)-coupled P2Y(11) receptors are involved in both fast and slow relaxations. These P2Y receptor subtypes, plus neuronal P2X receptors, may explain the phenomenon of parasympathetic inhibition first described by Langley (1898).

PKA-dependent activation of the vascular smooth muscle isoform of KATP channels by vasoactive intestinal polypeptide and its effect on relaxation of the mesenteric resistance artery

Vasoactive intestinal polypeptide (VIP) is a potent vasodilator and has been successfully used to alleviate hypertension. Consistently, disruption of VIP gene in mice leads to hypertension. However, its downstream targets in the vascular regulation are still not well demonstrated. To test the hypothesis that the vascular smooth muscle isoform of KATP channels is a downstream target of the VIP signaling, we performed the studies on the Kir6.1/SUR2B channel expressed in HEK293 cells. We found that the channel was strongly activated by VIP. Through endogenous VIP receptors, the channel activation was reversible and dependent on VIP concentrations with the midpoint-activation concentration approximately 10 nM. The channel activation was voltage-independent and could be blocked by KATP channel blocker glibenclamide. In cell-attached patches, VIP augmented the channel open-state probability with modest suppression of the single channel conductance. The VIP-induced Kir6.1/SUR2B channel activation was blocked by PKA inhibitor RP-cAMP. Forskolin, an adenylyl cyclase activator, activated the channel similarly as VIP. The effect of VIP was further evident in the native tissues. In acutely dissociated mesenteric vascular smooth myocytes, VIP activated the KATP currents in a similar manner as in HEK293 cells. In endothelium-free mesenteric artery rings, VIP produced concentration-dependent vasorelaxation that was attenuated by glibenclamide. These results therefore indicate that the vascular isoform (Kir6.1/SUR2B) of KATP channels is a target of VIP. The channel activation relies on the PKA pathway and produces mesenteric arterial relaxation.

Prostaglandin E2 enhances acetylcholine-induced, Ca2+-dependent ionic currents in swine tracheal mucous gland cells

Airway submucosal gland cell (SMGC) secretions are under the control of various neurotransmitters and hormones. Interactions between different pathways, such as those mediated by cAMP and Ca(2+), in controlling mucus or electrolyte secretions are not well understood. Prostaglandin E(2) (PGE(2)) or forskolin has been shown to enhance acetylcholine (ACh)-induced short circuit current (I(SC)) in SMGC mucous cell monolayers. We show that PGE(2), by activating cAMP-dependent protein kinase A (PKA), enhanced ACh-induced, Ca(2+)-mediated current and changes in [Ca(2+)](i) in mucous cells. PGE(2) pretreatment sensitized ACh-induced I(SC) (DeltaI(SC)) by activating endoprostanoid (EP(2)) receptors. PKA inhibitors 14-22 amide PKI (PKI) and Rp-diastereomer (Rp) of cAMPs prevented the effect of PGE(2). Removing external Ca(2+) or pretreatment with the Ca(2+) entry blocker, SKF96365 [1-[beta-(3-(4-methoxyphenyl) propoxy)-4-methoxyphenethyl]-1H-imidazole hydrochloride1-[2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl) propoxy] ethyl] imidazole], shifted the concentration-response relationships for ACh to the right but did not abolish PGE(2)-induced sensitization of the ACh response. An inositol 1,4,5-trisphosphate (IP(3)) receptor antagonist and Ca(2+) entry blocker, 2-aminoethoxydiphenyl borate, abolished the ACh-induced response. Charybdotoxin, but not iberiotoxin (IbTX), inhibited the ACh-induced DeltaI(SC). Clotrimazole, but not IbTX, inhibited the ACh-induced serosal K(+) current. Under whole-cell patch clamp, ACh-induced K(+) and Cl(-) currents were coincident with increases in [Ca(2+)](i) in single mucous cells. PGE(2) or forskolin pretreatment did not induce current or [Ca(2+)](i) changes but enhanced ACh-induced currents, membrane hyperpolarization, and [Ca(2+)](i) changes. Intra-cellular dialysis with the PKA-catalytic subunit enhanced ACh-induced whole-cell current as well. These findings demonstrate that PGE(2), via EP(2) receptors and the cAMP/PKA pathway, activates Ca(2+) entry-independent mechanisms, possibly by increasing IP(3)-mediated Ca(2+) release, resulting in the sensitization of ACh-induced currents.

Maxi-K potassium channels: form, function, and modulation of a class of endogenous regulators of intracellular calcium

Large-conductance calcium-activated (maxi-K, BK) potassium channels are widely distributed in the brain. Maxi-K channels function as neuronal calcium sensors and contribute to the control of cellular excitability and the regulation of neurotransmitter release. Little is currently known of any significant role of maxi-K channels in the genesis of neurological disease. Recent advances in the molecular biology and pharmacology of these channels have revealed sources of phenotypic variability and demonstrated that they can be successfully modulated by pharmacological agents. A potential role is suggested in the treatment of conditions such as ischemic stroke and cognitive disorders.

Motor control of airway goblet cells and glands

Activation of nerves increases airway mucus secretion. The mucus derives from submucosal glands and epithelial goblet cells. Depending upon species and airway level, innervation comprises parasympathetic (cholinergic), sympathetic (adrenergic) and 'sensory-efferent' pathways. In all species studied, cholinergic mechanisms predominate, particularly in human airways. Muscarinic M3 receptors on the secretory cells mediate the cholinergic response. Tachykinins (substance P and neurokinin A) mediate the sensory-efferent response, acting via tachykinin NK1 receptors. Endogenous mechanisms regulate the magnitude of neurogenic secretion, including enzymes (degrade neurotransmitters), nitric oxide (NO) and vasoactive intestinal peptide (VIP) (regulate stimulated secretion), and muscarinic M2 autoreceptors (inhibit acetylcholine release). Exogenous opioids also inhibit neurogenic secretion prejunctionally. Both VIP and opioids act by opening large conductance, calcium-activated potassium (BK(Ca)) channels. Present understanding of neural control of mucus secretion in animal airways requires translation into human data. This information should lead to rational development of drugs for bronchial diseases in which neurogenic mucus hypersecretion contributes to pathophysiology, including chronic bronchitis and asthma.

Effect of vasoactive intestinal peptide (VIP)-related peptides on cholinergic neurogenic and direct mucus secretion in ferret trachea in vitro

1 We investigated whether vasoactive intestinal peptide (VIP) and its related peptides, pituitary adenylate cyclase activating peptide (PACAP) and secretin, regulate cholinergic neural mucus secretion in ferret trachea in vitro, using 35SO4 as a mucus marker. We also studied the interaction between VIP and secretin on cholinergic mucus output. 2 VIP (1 and 10 microM) increased secretion, whereas neither PACAP1 - 27, PACAP1 - 38 nor secretin (up to 10 microM) increased mucus output. In contrast, VIP, PACAP1 - 27 and PACAP1 - 38 concentration-dependently inhibited cholinergic neural secretion, with an order of potency of VIP>PACAP 1 - 38>PACAP1 - 27. Neither PACAP1 - 27 nor PACAP1 - 38 altered the secretion induced by acetylcholine (ACh). 3 Secretin increased cholinergic neural secretion with a maximal increase of 190% at 1 microM. This potentiation was blocked by VIP or atropine. Similarly, secretin (1 microM) potentiated VIP (1 microM)-induced mucus output by 160%. Secretin did not alter exogenous ACh-induced secretion. VIP vs secretin competition curves suggested these two peptides were competing reversibly for the same receptor. 4 We conclude that, in ferret trachea in vitro, VIP and PACAPs inhibit cholinergic neural secretion via pre-junctional modulation of cholinergic neurotransmission. VIP and secretin compete for the same receptor, possibly a VIP1 receptor, at which secretin may be a receptor antagonist.