Jpn. J. Pharmacol. 87 (3), 208-213 (2001)
Effects of Calcium Antagonists on the Nitrergic Nerve Function in Canine Corpus Cavernosum
Tomio Okamura*, Hideyuki Fujioka and Kazuhide Ayajiki
Department of Pharmacology, Shiga University of Medical Science, Seta, Ohtsu 520-2192, Japan
*Corresponding author. FAX: +81-77-548-2183, E-mail: firstname.lastname@example.org
Abstract: Effects of calcium antagonists on nitrergic nerve function were examined in the isolated canine corpus cavernosum. In the cavernous strips precontracted with phenylephrine, transmural electrical stimulation elicited frequency-dependent (2-5 Hz) relaxations that were abolished by NG-nitro-L-arginine (10-5 M), a nitric oxide (NO) synthase inhibitor; 1H[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ, 10-6 M), a soluble guanylate cyclase inhibitor; and tetrodotoxin (3 ´ 10-7 M). The relaxations were not affected by treatment with nifedipine or nicardipine (10-8-10-6 M), L-type specific calcium channel inhibitors, but were significantly inhibited by amlodipine or cilnidipine, inhibitors of L- plus N-type calcium channels, in a concentration-related manner (10-7-10-6 M). All of the inhibitors used did not affect the relaxations induced by exogenous NO (acidifed NaNO2). These findings suggest that N-type, but not L-type, calcium channels are responsible for increasing cytosolic free calcium, a prerequisite for the synthesis of NO, in the nitrergic dilator nerves innervating the corpus cavernosum.
Keywords: Corpus cavernosum, Nitrergic nerve, Transmural electrical stimulation, Calcium antagonist, Smooth muscle relaxation
[Back to TOC]