title: Prostaglandin E2 excitatory effects on guinea pig urinary bladder smooth muscle: a novel regulatory mechanism mediated by large-conductance voltage- and Ca2+-activated K+ channels.
abstract: Prostaglandin E2 (PGE2) is an essential signaling molecule involved in the regulation of detrusor smooth muscle (DSM) function. However, the underlying regulatory mechanism by which PGE2 augments DSM cell excitability and contractility is not well understood. Here, we investigated whether PGE2 inhibits the large conductance voltage- and Ca(2+)-activated K(+) (BK) channels in guinea pig DSM, thereby increasing DSM excitability and contractility. We used a multidisciplinary experimental approach including amphotericin-B perforated patch-clamp electrophysiology and live-cell Ca(2+) imaging in native freshly-isolated DSM cells, isometric tension recordings of intact DSM strips, and pharmacological tools to investigate BK channel regulation by PGE2 in guinea pig DSM. PGE2 increased the spontaneous phasic contractions of isolated DSM strips in a concentration-dependent manner (10 nM-10 µM). BK channel inhibition with paxilline (1 µM) attenuated the PGE2-induced DSM phasic contractions, suggesting that BK channels are involved in the mechanism of PGE2-induced DSM contractions. PGE2 (10 µM) increased the intracellular Ca(2+) levels in freshly-isolated DSM cells. PGE2 (10 µM) also caused an inhibition of the amplitude and frequency of spontaneous transient BK currents in DSM cells. Moreover, PGE2 (10 µM) did not affect the amplitude of whole cell steady-state BK currents in DSM cells. Our findings provide strong experimental evidence that PGE2 leads to an inhibition of the spontaneous transient BK currents, elevation of intracellular Ca(2+) levels in freshly-isolated DSM cells, and augmentation of DSM phasic contractions. Thus, we have revealed a novel mechanism that BK channels mediate PGE2-induced contractions in guinea pig DSM.
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Coker Life Sciences Building, Room 609D, 715 Sumter St, Columbia, SC 29208, United States.
authors.forename: Shankar P
authors.initials: SP
authors.lastname: Parajuli
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Coker Life Sciences Building, Room 609D, 715 Sumter St, Columbia, SC 29208, United States.
authors.forename: Aaron
authors.initials: A
authors.lastname: Provence
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Coker Life Sciences Building, Room 609D, 715 Sumter St, Columbia, SC 29208, United States. Electronic address: petkov@cop.sc.edu.
authors.forename: Georgi V
authors.initials: GV
authors.lastname: Petkov
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D015232:Dinoprostone / Q000494:pharmacology*; D055724:Electrophysiological Phenomena / Q000187:drug effects; D006168:Guinea Pigs; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D001743:Urinary Bladder / Q000187:drug effects* / Q000502:physiology*
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D015232:Dinoprostone; D002118:Calcium
keywords: Ca(2+) imaging; Detrusor; Patch-clamp; Prostaglandin E(2)