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

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 (E-Cl) and was reduced by anthracene-9-carboxylic acid (A9C; 1 mm) and niflumic acid (100 muM), suggesting that it was a Ca2+-activated Cl- current. When held constantly at -60mV, over 70% of cells fired spontaneous transient inward currents (STICs), the amplitudes of which were reduced by A9C and niflumic acid. STICs reversed near E-Cl 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.