Potassium outward currents in freshly dissociated rabbit corpus cavernosummyocytes

Purpose: Cavernous smooth muscle cells have a key role in the control of pe nile erection and detumescence. In this study the types of smooth muscle ce lls and currents present in isolated rabbit corpus cavernosum myocytes were characterized. Materials and Methods: Immunohistochemical methods were used to identify ca vernous smooth muscle cells. Currents were recorded from freshly dissociate d myocytes using the whole cell and amphotericin perforated patch clamp tec hniques. Results: Cavernous myocytes were identified by a-smooth muscle actin and sm ooth muscle myosin immunoreactivity. Based on electrical properties at leas t 2 types of myocytes were present. Type I cells showed more depolarized me mbrane potentials, lower capacitance, higher input resistance and increased current densities at positive potentials than type II cells. In types I an d II cells at voltages positive to 30 mV, maxi K+ channel (Ca2+ activated l arge conductance K+ channel or BK) blockade with iberiotoxin or charybdotox in reduced outward currents by approximately 40% to 80% at 80 mV. Maxi K+ c hannel blocking did not affect cell membrane potential. Type II cells showe d delayed rectifier K+ channel-type outward currents that were not detected in type I cells. Delayed rectifier K+ channel-type currents were resistant to iberiotoxin or charybdotoxin, activated at approximately -50 to -40 mV. and inactivated weakly. Conclusions: The data suggest that cavernous smooth muscle cells are hetero geneous with at least 2 subtypes identified based on membrane potential, ca pacitance, input resistance, current density and delayed rectifier K+ chann el expression. The activation threshold suggests that delayed rectifier Kchannels are open at the resting membrane potential and, therefore, contrib ute to control and regulation of the cavernous myocyte excitability.