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