Cyclic AMP‐mediated regulation of excitation‐contraction coupling in canine gastric smooth muscle.

Abstract

SUMMARY1. Agonists known to increase cyclic AMP levels in gastrointestinal smooth muscles were studied in isolated circular muscles of the canine antrum to investigate the mechanisms of the inhibitory effects of these agents.2. Muscles were electrically active, generating typical slow wave activity.

Post‐receptor pathway of the ATP‐induced relaxation in smooth muscle of the mouse vas deferens

“…ATP-induced relaxation of depolarized VD was correlated with a reduction of the level of PMLC. Most likely this reflected the inhibition of the myosin light chain kinase (MLCK) when it is phosphorylated by a cyclic AMP-dependent protein kinase A (Adelstein et al, 1978;Kerrick & Hoar, 1981;Nishimura & van Bremen, 1989;Ozaki et al, 1992) On the basis of the rank order of potency of different ATP analogues, of the absence of tachyphylaxis and of the action of selective antagonists, it was proposed that ATP-induced relaxation implies a P2Y-like purinoceptor (Boland et al, 1992). Our results suggest that this effect is linked to the activation of adenylyl cyclase.…”

Isoproterenol Changes the Relationship between Cytosolic Ca2+and Contraction in Guinea Pig Taenia Caecum

“…The agents that increase cyclic AMP (ISO, VIP, CGRP and forskolin) and cyclic GMP (sodium nitroprusside) in gastric muscle produced inhibition of electrical slow waves, Ca" transients, mechanical activ ities and Ca" sensitivity of contractile elements (5,33). Thus, it is possible that not only cyclic AMP but also cyclic GMP may contribute to the inhibitory effects of ISO in taenia.…”

Modulation of voltage‐dependent Ba2+ currents in the guinea‐pig gastric antrum by cyclic nucleotide‐dependent pathways

“…In other intestinal smooth muscles, cAMP (or db-cAMP) had no effect on the amplitudes of voltage-dependent Ca 2 þ currents generated by L-type Ca 2 þ channels (rabbit jejunum, Ohya et al, 1987;guinea-pig taeniacoli, Muraki et al, 1993). An inhibition of L-type Ca 2 þ channels was proposed in guinea-pig gastric smooth muscle (Ozaki et al, 1992). Several inhibitory agonists that activate adenylate cyclase (such as b-adrenergic stimulators, forskolin, VIP, CGRP, etc.)…”

“…were found to decrease the increases in [Ca 2 þ ] i associated with each slow wave and inhibit contraction. Although it was suggested that this might result from an inhibition of Ca 2 þ influx during each slow wave (Ozaki et al, 1992), a direct test of this idea was not attempted.…”