Neuroeffector transmission to different layers of smooth muscle in the rat penile bulb

Abstract

Using intracellular recording techniques, two distinct layers of smooth muscle were identified in the rat penile bulb. The inner muscle layer (parenchyma) exhibited spontaneous action potentials, while the outer sheet (sac) was electrically quiescent. In the parenchyma, transmural stimulation initiated non‐adrenergic, non‐cholinergic (NANC) inhibitory junction potentials (IJPs) which were abolished by Nωnitro‐L‐arginine (LNA) or 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ). The amplitude of IJPs was reduced by ouabain, dinitrophenol or decreasing the extracellular potassium concentration ([K+]o) but not by several K+ channel blockers. The parenchyma also received an excitatory innervation mediated by α‐adrenoceptors which caused a contraction that was not associated with a membrane potential change. In the sac, transmural stimulation initiated two component excitatory junction potentials (EJPs) mediated by α‐adrenoceptors and associated action potentials. The initial component was more dramatically suppressed than the secondary component by caffeine, ryanodine or cyclopiazonic acid (CPA). Lowering of the extracellular chloride concentration ([Cl−]o) selectively inhibited the rapid component of EJPs, while niflumic acid was less potent. These results suggest that IJPs in the parenchyma result from the release of NO which stimulates sodium pump activity following the activation of guanylate cyclase. In the sac, the activation of α‐adrenoceptors initiates EJPs by releasing Ca2+ from intracellular stores which activates Ca2+‐activated channels.

The relaxant actions of ethanolic extract of Tridax procumbens (Linn.) on rat corpus cavernosum smooth muscle contraction

“…From our observations that ethanolic leaf extract of T. procumbens induces corporal relaxation responses in contractions produced by either of the agonists, it suggested that T. procumbens extract blocks Ca 2+ influx through interference with both voltage-and receptor-operated channels. Ca 2+ transients with the action potentials observed in this study were consistent with previous reports on corpus spongiosum smooth muscle [18,22]. This indicates that the activation of l-type Ca 2+ channels may be a fundamental process of spontaneous activity in CCSM.…”

The Effects of Superoxide Anion Generators on Responses to Exogenous Nitric Oxide and Non‐Adrenergic, Non‐Cholinergic Nerve Stimulation in Rat Isolated Penile Bulb

“…It does not exist in rabbit, while in man it is a slight enlargement of the proximal part of corpus spongiosum and in rat it is much more prominent (Hayes 1965). Canine (Hedlund et al 1995) and rat (Hashitani 2000) penile bulbs have been found to receive rich NANC innervation mediated by L‐arginine‐nitric oxide pathway similar to the corpus cavernosum . Consistently, in the present study we found that electrically‐induced relaxations of rat penile bulbs were abolished after incubation with tetrodotoxin and inhibited by the addition of L‐NAME indicating that they are neural in origin and are mediated by L‐arginine/nitric oxide pathway.…”

Mechanisms of Penile Erection and Basis for Pharmacological Treatment of Erectile Dysfunction

“…A variety of ion channels have been identified in CC smooth muscle cells, but there have been few electrophysiological investigations of whole corporal smooth muscle preparations ). In the proximal part of the rat corpus spongiosum (penile bulb), Hashitani (2000) demonstrated spontaneous action potentials in the inner muscle layer. On the other hand, no action potentials could be detected by electrophysiological investigation of cultured human CC smooth muscle cells (Christ et al, 1993).…”