Activity of glibenclamide-sensitive K+ channels under unstimulated conditions in smooth muscle cells of pig proximal urethra

Abstract

The membrane potential in pig proximal urethra was examined by use of the microelectrode technique. In cells 1–2cm from the bladder neck the membrane potential was quiescent, with a value of –37.2±2.5 mV (n=16). In some cells small spontaneous de- and hyperpolarizations were seen. Glibenclamide (1μM) caused a small but significant depolarization in tissue strips (12±3mV, n=3) and also in dispersed cells using whole-cell patch electrodes (13±3mV, n=5). In the conventional whole-cell voltage-clamp configuration, glibenclamide reduced the noise level of the basal membrane current at –50mV and inhibited the membrane current in symmetrical 140mM K⁺ conditions. In cell-attached patches, brief openings of a glibenclamide-sensitive 43pS K⁺ channel (K_GS-43pS) were seen even under unstimulated conditions and greater activation occurred in the same membrane patch on subsequent application of 100μM levcromakalim. These results provide direct evidence that glibenclamide-sensitive K⁺ channels may play a role in maintaining the resting membrane potential of pig proximal urethra under unstimulated conditions.