1. ¹Department of Physiology and Biophysics, Seoul National University College of Medicine, Seoul, Korea
2. ²Department of Urology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea

Correspondence: SW Lee, Department of Urology, Samsung Medical Center, Sungkyunkwan University School of Medicine, #50 Ilwon-dong Kangnan-ku, Seoul 135-710, Korea. E-mail: drswlee@smc.samsung.co.kr

Received 18 February 2003; Revised 8 April 2003; Accepted 15 April 2003.

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 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 42.02.6 pS which is an intermediate conductance between that of either Kir6.1 or Kir6.2. The pinacidil (10 M) increased the magnitude of the outward K⁺ current (214.689.2%, n=12, P<0.05), which was blocked by the subsequent addition of the specific K_ATP channel subtype selective blocker, glibenclamide (10 M). The SIN-1(200 M) induced increases in whole-cell outward K⁺ currents (126.01.4%, n=4). The increased currents by SIN-1 were inhibited by glibenclamide (10 M). 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.