Characterization of spontaneous depolarizations in smooth muscle cells of the Guinea pig prostate

PURPOSE: We characterized the electrical events recorded in small segments of the dorsal lobe of the prostate of immature male guinea pigs and examined some mechanisms underlying their generation. MATERIAL AND METHODS: Membrane potential recordings were made in the stroma of the guinea pig prostate using conventional single microelectrode techniques. RESULTS: Three distinct, spontaneously occurring electrical events were recorded in guinea pig prostate, namely slow waves, consisting of a depolarizing transient 14 mV in amplitude with 1 to 6 nifedipine sensitive spikes superimposed, pacemaker potentials, consisting of a larger depolarization 40 mV in amplitude, and STDs 1 to 10 mV in amplitude. Only spikes on slow waves were inhibited by nifedipine. The depolarizing transient of slow waves, pacemaker potentials and STDs were abolished by cyclopiazonic acid, a blocker of the SERCA pump, and the mitochondrial uncoupler cyanide m-chlorophenyl hydrazone as well as upon exposure to Ca(2+)-free saline or the Cl(-) channel blockers niflumic acid and anthracene-9-carboxylic acid (Sigma Chemical Co., St. Louis, Missouri). Examination of the stochastic properties of STDs revealed that they were not well modeled by Poisson statistics, but rather they occurred in a clustered manner, such they may well underlie pacemaker potential generation. CONCLUSIONS: Guinea pig prostate shows STD and pacemaker potentials that arise from the release of Ca(2+) from intracellular stores and the activation of Ca(2+) activated Cl(-) channels. We speculate that the depolarizing transient of prostatic slow waves is the propagated response of pacemaker potentials evoked at sites electrically distant from the recording electrode.