Characterization of ATP-sensitive potassium channels in human corporal smooth muscle cells

Abstract

Potassium (K) channels play a significant role in modulating human corporal smooth muscle tone, and thus, erectile capacity. Recent pharmacological studies indicate that the metabolically-regulated K channel (K_ATP) may be an important modulator of human penile erection with significant therapeutic potential. The goal of these initial studies, therefore, was to utilize patch clamp techniques to characterize the putative K_ATP subtype(s) present in cultured and freshly isolated human corporal smooth muscle cells. In the cell-attached patch mode, two distinct unitary K⁺ currents were identified whose respective conductance values were similar in cultured and freshly isolated smooth muscle cells. In cultured myocytes, the measured conductance values in symmetric KCl (140 mM) solutions were 59.1±2.7 pS and 18.4±2.1 pS (n=5 cells). Under identical experimental conditions in freshly isolated myocytes, corresponding conductance values were 59.2±3.7 pS and 18.5±2.4 pS, respectively (n=4 cells). I-V curves constructed during step depolarization (−60 to +80 mV), revealed a linear I-V relationship for both unitary conductances. Single channel records documented that both conductances were reversibly inhibited by the application of ATP (1–3 mM) to the bath solution in the inside-out attached patch configuration. The unitary activity of both K channel subtypes was significantly increased by the application of pinacidil (10 μM) and levcromakalim (10 μM). Whole cell patch recordings documented a glibenclamide-sensitive, pinacidil- and levcromakalim-induced increase in the whole cell outward K⁺ current during step depolarization (−70 mV to +130 mV) of 105±37%, 139±42%, respectively. These data confirm and extend our previous observations, and provide the first evidence for the presence of K_ATP channel subtypes in human corporal smooth muscle cells.