The detection of focal Ca2+ transients (called neuroeffector Ca2+ transients, or NCTs) in smooth muscle of the mouse isolated vas deferens has been used to detect the packeted release of ATP from nerve terminal varicosities acting at postjunctional P2X receptors. The present study investigates the sources and sequestration of Ca2+ in NCTs. Smooth muscle cells in whole mouse deferens were loaded with the Ca2+ indicator Oregon Green 488 BAPTA‐1 AM and viewed with a confocal microscope. Ryanodine (10 µm) decreased the amplitude of NCTs by 45 ± 6 %. Cyclopiazonic acid slowed the recovery of NCTs (from a time course of 200 ± 10 ms to 800 ± 100 ms). Caffeine (3 mm) induced spontaneous focal smooth muscle Ca2+ transients (sparks). Neither of the T‐type Ca2+ channel blockers NiCl2 (50 µm) or mibefradil dihydrochloride (10 µm) affected the amplitude of excitatory junction potentials (2 ± 5 % and −3 ± 10 %) or NCTs (−20 ± 36 % and 3 ± 13 %). In about 20 % of cells, NCTs were associated with a local, subcellular twitch that remained in the presence of the α1‐adrenoceptor antagonist prazosin (100 nm), showing that NCTs can initiate local contractions. Slow (5.8 ± 0.4 µm s−1), spontaneous smooth muscle Ca2+ waves were occasionally observed. Thus, Ca2+ stores initially amplify and then sequester the Ca2+ that enters through P2X receptors and there is no amplification by local voltage‐gated Ca2+ channels.

1 Recently, a population of nerves has been described in the aganglionic mouse vas deferens, in which electrically evoked contractions were insensitive to high concentrations of the adrenergic neurone blocker, bretylium. In this paper, the pharmacology of this nerve-evoked contraction has been examined in more detail. 2 Bretylium (20 mM) revealed, after 5 h exposure, a new residual neurogenic contraction (20 stimuli at 10 Hz) that was tetrodotoxin-sensitive. 3 The muscarinic antagonist, cyclopentolate (0.1 and 1 mM), reduced this residual component and the inhibition was reversed by the acetylcholinesterase inhibitor, neostigmine (1 and 10 mM). 4 Nicotine (30 mM) enhanced the residual component revealed by bretylium, suggesting that there are prejunctional nicotinic receptors (nAchRs) influencing acetylcholine (Ach) release. 5 In the presence of prazosin (0.1 mM), a selective a 1 -adrenoceptor antagonist, and a,b-methylene ATP (1 mM), a purinergic agonist that desensitise P2X receptors, neostigmine increased the hump component of contraction and yohimbine (0.3 mM), an a 2 -adrenoceptor antagonist, enhanced both components of the electrically evoked stimulation. The contraction was blocked by cyclopentolate (1 mM). 6 In the absence of bretylium, neostigmine alone increased the hump component of contraction in a frequency-dependent manner. This increase was reversed by atropine (1 mM) and cyclopentolate (1 mM) to control levels. However, in control experiments, atropine or cyclopentolate did not detectably influence the delayed neurogenic contraction. 7 Ach (10 mM) induced a contraction in the mouse vas deferens, either when applied alone or in the presence of neostigmine. 8 Thus, it has been demonstrated unequivocally that the mouse vas deferens is innervated by functional cholinergic nerves, whose action is terminated by cholinesterase. Furthermore, Ach release can be enhanced by activation of prejunctional nAchRs presumably located on the cholinergic nerve terminals.

In isolated guinea pig perfused hearts ICI 118.551, a selective beta 2 adrenoceptor antagonist, induced transient ventricular extrasystoles. Following the termination of the perfusion, a very significant increase of both the ventricular fibrillation threshold and the refractory periods were measured. In guanethidine pretreated hearts, ICI 118.551 failed to induce premature beats. At the same time the fibrillation threshold and refractory periods exhibited a very significant decrease. The perfusion of equimolecular concentration of metoprolol, a beta-1-adrenoceptor antagonist, and (+) propranolol, a quinidine-like compound, induced, in most experimental settings, similar results as ICI 118.551. Thus, besides its beta-2-adrenoceptor antagonist properties, ICI 118.551 presented other pharmacological actions.

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