Ethanol-mediated relaxation of guinea pig urinary bladder smooth muscle: involvement of BK and L-type Ca2+ channels

Abstract

Mechanisms underlying ethanol (EtOH)-induced detrusor smooth muscle (DSM) relaxation and increased urinary bladder capacity remain unknown. We investigated whether the large conductance Ca2+-activated K+ (BK) channels or L-type voltage-dependent Ca2+ channels (VDCCs), major regulators of DSM excitability and contractility, are targets for EtOH by patch-clamp electrophysiology (conventional and perforated whole cell and excised patch single channel) and isometric tension recordings using guinea pig DSM cells and isolated tissue strips, respectively. EtOH at 0.3% vol/vol (∼50 mM) enhanced whole cell BK currents at +30 mV and above, determined by the selective BK channel blocker paxilline. In excised patches recorded at +40 mV and ∼300 nM intracellular Ca2+ concentration ([Ca2+]), EtOH (0.1–0.3%) affected single BK channels (mean conductance ∼210 pS and blocked by paxilline) by increasing the open channel probability, number of open channel events, and open dwell-time constants. The amplitude of single BK channel currents and unitary conductance were not altered by EtOH. Conversely, at ∼10 μM but not ∼2 μM intracellular [Ca2+], EtOH (0.3%) decreased the single BK channel activity. EtOH (0.3%) affected transient BK currents (TBKCs) by either increasing frequency or decreasing amplitude, depending on the basal level of TBKC frequency. In isolated DSM strips, EtOH (0.1–1%) reduced the amplitude and muscle force of spontaneous phasic contractions. The EtOH-induced DSM relaxation, except at 1%, was attenuated by paxilline. EtOH (1%) inhibited L-type VDCC currents in DSM cells. In summary, we reveal the involvement of BK channels and L-type VDCCs in mediating EtOH-induced urinary bladder relaxation accommodating alcohol-induced diuresis.