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

Abstract

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 KATP channel in the modulation of corporal smooth muscle tone, there is a shortage of information available about the KATP 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 KATP 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 KATP channel under the condition of intracellular and extracellular 140mM [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 μM) increased the magnitude of the outward K+ current (214.6 γ 89.2%, n = 12, P < 0.05), which was blocked by the subsequent addition of the specific KATP channel subtype selective blocker, glibenclamide (10 μM). The SIN-1(200 μM) induced increases in whole-cell outward K+ currents (126.0 γ 1.4%, n = 4). The increased currents by SIN-1 were inhibited by glibenclamide (10 μM). We are the first to show that KATP 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 KATP 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.