Modulation of spontaneous Ca2+-activated Cl− currents in the rabbit corpus cavernosum by the nitric oxide–cGMP pathway

摘要

The whole-cell perforated patch clamp technique was used to study membrane currents in isolated rabbit corpus cavernosum smooth muscle cells. Depolarization from −80 mV to the range −40 to −10 mV evoked a nifedipine-sensitive Ca²⁺ current that was followed by a slower inward current that activated over several hundred milliseconds. The slow current reversed near the Cl⁻ equilibrium potential (ECl) and was reduced by anthracene-9-carboxylic acid (A9C; 1 mm) and niflumic acid (100 μm), suggesting that it was a Ca²⁺-activated Cl⁻ current. When held constantly at −60 mV, over 70% of cells fired spontaneous transient inward currents (STICs), the amplitudes of which were reduced by A9C and niflumic acid. STICs reversed near ECl in a symmetrical Cl⁻ gradient and when [Cl⁻]o was substituted with glutamate or I⁻, the reversal potential shifted to more positive or more negative values, respectively, confirming that STICs were mediated by Cl⁻ channels. STICS were also blocked by cyclopiazonic acid, 2-aminoethoxydiphenyl borate (2-APB) and 2-nitro-4-carboxyl-N,N-diphenylcarbamate (NCDC), suggesting that they depended on IP3-mediated Ca²⁺-release from the sarcoplasmic reticulum. Modulation by the NO–cGMP pathway was investigated by applying nitrosocysteine, 3-(5-hydroxymethyl-2-furyl)-1-benzyl indazole (YC-1), and 8-bromo cGMP, all three of which abolished STIC activity. YC-1 also reduced noradrenaline-evoked inward currents, but had no effect on similar currents evoked by caffeine, suggesting that cGMP selectively inhibited IP3-mediated Ca²⁺ release. We propose that Ca²⁺-activated Cl⁻ currents underlie detumescent tone in the corpus cavernosum, and that modulation of this mechanism by the NO–cGMP pathway is important during penile erection.