vasoactive-intestinal-peptide and iberiotoxin

1. The aims of this study were to determine: (1) whether vasoactive intestinal peptide (VIP) regulates cholinergic and 'sensory-efferent' (tachykininergic) 35SO4 labelled mucus output in ferret trachea in vitro, using a VIP antibody, (2) the class of potassium (K+) channel involved in VIP-regulation of cholinergic neural secretion using glibenclamide (an ATP-sensitive K+ (K(ATP)) channel inhibitor), iberiotoxin (a large conductance calcium activated K+ (BK(ca)) channel blocker), and apamin (a small conductance K(ca) (SK(ca)) channel blocker), and (3) the effect of VIP on cholinergic neurotransmission using [3H]-choline overflow as a marker for acetylcholine (ACh) release. 2. Exogenous VIP (1 and 10 microM) alone increased 35SO4 output by up to 53% above baseline, but suppressed (by up to 80% at 1 microM) cholinergic and tachykininergic neural secretion without altering secretion induced by ACh or substance P (1 microM each). Endogenous VIP accounted for the minor increase in non-adrenergic, non-cholinergic (NANC), non-tachykininergic neural secretion, which was compatible with the secretory response of exogenous VIP. 3. Iberiotoxin (3 microM), but not apamin (1 microM) or glibenclamide (0.1 microM), reversed the inhibition by VIP (10 nM) of cholinergic neural secretion. 4. Both endogenous VIP (by use of the VIP antibody; 1:500 dilution) and exogenous VIP (0.1 microM), the latter by 34%, inhibited ACh release from cholinergic nerve terminals and this suppression was completely reversed by iberiotoxin (0.1 microM). 5. We conclude that, in ferret trachea in vitro, endogenous VIP has dual activity whereby its small direct stimulatory action on mucus secretion is secondary to its marked regulation of cholinergic and tachykininergic neurogenic mucus secretion. Regulation is via inhibition of neurotransmitter release, consequent upon opening of BK(Ca) channels. In the context of neurogenic mucus secretion, we propose that VIP joins NO as a neurotransmitter of i-NANC nerves in ferret trachea.

Topics: Acetylcholine; Adrenergic Agents; Animals; Antibodies; Atropine; Chymotrypsin; Dose-Response Relationship, Drug; Ferrets; In Vitro Techniques; Male; Mucus; Muscarinic Antagonists; Neurotransmitter Agents; Peptides; Phentolamine; Piperidines; Potassium Channels; Propranolol; Receptors, Adrenergic; Receptors, Cholinergic; Receptors, Tachykinin; Trachea; Tritium; Vasoactive Intestinal Peptide

We investigated the functional relevance of large conductance voltage-dependent and Ca(2+)-sensitive K(+)(MaxiK) channels in vasoactive intestinal peptide (VIP)-induced relaxation of rat mesenteric artery. VIP, which is known to increase cAMP levels, produced a concentration-dependent relaxation in endothelium-denuded arteries. Iberiotoxin, a MaxiK channel blocker, greatly diminished the VIP-induced relaxation. In a similar manner, a significant portion of the relaxant response to dibutyryl-cAMP (DBcAMP), a membrane-permeable analog of cAMP, was inhibited by iberiotoxin. These results suggest that activation of MaxiK channels significantly contributes to the relaxant response of rat mesenteric artery to VIP, possibly via cAMP-mediated pathways.

Topics: Animals; Bucladesine; Male; Mesenteric Arteries; Peptides; Potassium Channels; Rats; Rats, Wistar; Toxins, Biological; Vasoactive Intestinal Peptide; Vasodilation

To examine synergistic interactions among naturally occurring vasodilators, we investigated the effects of i.v. infusion of adrenomedullin (ADM) alone and in combination with low-dose vasoactive intestinal polypeptide (VIP) or calcitonin gene-related peptide (CGRP) on adenosine-induced vasodepression in rats. I.v. infusion of the combination of low-dose ADM (0.1 ng kg(-1) min(-1)) and VIP (3 ng kg(-1) min(-1)), as well as that of ADM (1 ng kg(-1) min(-1)) alone, significantly enhanced the vasodepressor responses to bolus i.v. doses of adenosine (3-100 microg kg(-1)), but not those to acetylcholine (0.1 microg kg(-1)). The observed potentiation did not occur in the presence of glibenclamide (20 mg kg(-1) i.v.), an antagonist of K(ATP) channels. Simultaneous i.v. infusion of low-dose ADM and CGRP (0.1 ng kg(-1) min(-1)) failed to enhance the effects of adenosine as well as acetylcholine. In the whole-cell voltage clamp experiments using single cells of the rat mesenteric artery, ADM (10(-11)-10(-7) M) as well as CGRP (10(-11)-10(-7) M) produced increases of inward current in a concentration-dependent manner. The ADM-induced current was not affected by iberiotoxin, a specific blocker of large conductance Ca2+-activated K+ channels, but suppressed markedly by glibenclamide and CGRP(8-37), a selective antagonist of CGRP1 receptors. From the results, we conclude that several naturally occurring vasodilators involving ADM synergistically interact, probably in link with K(ATP) channels, and furthermore that ADM may act, in part through CGRP1 receptor activation.

Topics: Adenosine; Adenosine Triphosphate; Adrenomedullin; Animals; Blood Pressure; Calcitonin Gene-Related Peptide; Cell Membrane; Dose-Response Relationship, Drug; Evoked Potentials; Glyburide; Heart Rate; Hypoglycemic Agents; Injections, Intravenous; Male; Membrane Potentials; Mesenteric Arteries; Muscle, Smooth, Vascular; Patch-Clamp Techniques; Peptides; Potassium Channels; Rats; Rats, Sprague-Dawley; Vasoactive Intestinal Peptide; Vasodilator Agents