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

The membrane potential in pig proximal urethra was examined by use of the microelectrode technique. In cells 1-2 cm 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 (1 microM) caused a small but significant depolarization in tissue strips (12+/-3 mV, n = 3) and also in dispersed cells using whole-cell patch electrodes (13+/-3 mV, n = 5). In the conventional whole-cell voltage-clamp configuration, glibenclamide reduced the noise level of the basal membrane current at -50 mV and inhibited the membrane current in symmetrical 140 mM K+ conditions. In cell-attached patches, brief openings of a glibenclamide-sensitive 43 pS K+ channel (K(GS)-43 pS) were seen even under unstimulated conditions and greater activation occurred in the same membrane patch on subsequent application of 100 microM 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.