Novel BK channel regulatory mechanism by protein kinase C in guinea pig urinary bladder smooth muscle (865.1)

Abstract

Large conductance Ca2+‐activated K+ (BK) channels are critical regulators of urinary bladder smooth muscle (UBSM) function. Here, we provide a novel mechanistic insight into BK channel regulation by protein kinase C (PKC) in UBSM. Voltage‐clamp experiments showed that pharmacological activation of PKC with phorbol 12‐myristate 13‐acetate (PMA), inhibited the spontaneous transient BK currents (TBKCs) in native freshly‐isolated guinea pig UBSM cells. Current‐clamp recordings revealed that PMA significantly depolarized UBSM membrane potential, and reduced the spontaneous transient hyperpolarizations in UBSM cells. The PMA inhibitory effects on UBSM membrane potential were abolished by the selective BK channel inhibitor paxilline and were not observed with its inactive analog, 4‐alpha‐PMA. PMA did not affect the amplitude of the whole cell steady‐state BK current or single BK channel open probability (recorded in cell‐attached mode) upon inhibition of all major Ca2+ sources for BK channel activation with thapsigargin, ryanodine, and nifedipine. PMA elevated the intracellular Ca2+ levels in UBSM cells, and increased spontaneous phasic and nerve‐evoked contractions of UBSM isolated strips. The results support the concept that PKC activation leads to a reduction in BK channel activity in UBSM via a Ca2+‐dependent mechanism, thus increasing UBSM contractility.Grant Funding Source: Supported by R01 DK084284 to G. V. Petkov