Molecular basis and characteristics of KATP channel in human corporal smooth muscle cells

Relaxation of the corpus cavernosum smooth muscle is an absolute prerequisite for penile erection. Potassium channels play a role in the physiologic regulation of corporal smooth muscle tone. In spite of the physiological importance of K-ATP channel in the modulation of corporal smooth muscle tone, there is a shortage of information available about the K-ATP channel subtype(s) present in the corporal smooth muscle. The purpose of this study was to investigate the subunit type of K-ATP channel, that is, the combinations of the Kir subunit and the SUR subunit in the human corporal smooth muscle and determine whether the electrophysiological kinetics and pharmacological properties of K-ATP channels meet the subunit characteristics of the ion channel. We used cultured human corporal smooth muscle cells. To determine the presence of Kir and SURs subunits, RT-PCR was performed using Kir6.1, Kir6.2, SUR1, SUR2A, and SUR2B gene-specific primers. For electrophysiological recordings, the whole-cell, inside-out, and cell-attached configurations of the patch-clamp technique were used. We observed transcripts for Kir6.1, Kir6.2, and SUR2B in mRNA isolated from smooth muscle cells of cultured human corpus carvernosum. We recorded the unitary K-ATP channel under the condition of intracellular and extracellular 140 mM [K+], and the slope conductance of the channel was 42.0 +/- 2.6 pS which is an intermediate conductance between that of either Kir6.1 or Kir6.2. The pinacidil (10 muM) increased the magnitude of the outward K+ current (214.6 +/- 89.2%, n = 12, P < 0.05), which was blocked by the subsequent addition of the specific K-ATP channel subtype selective blocker, glibenclamide (10 μM). The SIN-1(200 μM) induced increases in whole-cell outward K+ currents (126.0 +/- 1.4%, n = 4). The increased currents by SIN-1 were inhibited by glibenclamide (10 μM). We are the first to show that K-ATP channel in human corporal smooth muscle is composed of Kir6.1-Kir6.2 construct expressed with SUR2B by RT-PCR. These findings, taken together with the electrophysiological results, suggest that K-ATP channel in corporal smooth muscle cells is composed of heteromultimers of Kir6.1 and Kir6.2 with the ratio of 3 : 1 or 4 : 0 and SUR2B.