title: 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 Ca(2+)-activated K(+) (BK) channels or L-type voltage-dependent Ca(2+) 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 Ca(2+) concentration ([Ca(2+)]), 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 [Ca(2+)], 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.
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina.
authors.forename: John
authors.initials: J
authors.lastname: Malysz
authors.forename: Serge A Y
authors.initials: SA
authors.lastname: Afeli
authors.forename: Aaron
authors.initials: A
authors.lastname: Provence
authors.forename: Georgi V
authors.initials: GV
authors.lastname: Petkov
mesh_terms: D000818:Animals; D020746:Calcium Channels, L-Type / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D000431:Ethanol / Q000494:pharmacology*; D006168:Guinea Pigs; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009924:Organ Culture Techniques; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology*
chemical_list: D020746:Calcium Channels, L-Type; D051036:Large-Conductance Calcium-Activated Potassium Channels; D000431:Ethanol
keywords: alcohol; contractility; detrusor; patch-clamp; smooth muscle