title: Beta-adrenergic relaxation of mouse urinary bladder smooth muscle in the absence of large-conductance Ca2+-activated K+ channel.
abstract: In urinary bladder smooth muscle (UBSM), stimulation of beta-adrenergic receptors (beta-ARs) leads to activation of the large-conductance Ca2+-activated K+ (BK) channel currents (Petkov GV and Nelson MT. Am J Physiol Cell Physiol 288: C1255-C1263, 2005). In this study we tested the hypothesis that the BK channel mediates UBSM relaxation in response to beta-AR stimulation using the highly specific BK channel inhibitor iberiotoxin (IBTX) and a BK channel knockout (BK-KO) mouse model in which the gene for the pore-forming subunit was deleted. UBSM strips isolated from wild-type (WT) and BK-KO mice were stimulated with 20 mM K+ or 1 microM carbachol to induce phasic and tonic contractions. BK-KO and WT UBSM strips pretreated with IBTX had increased overall contractility, and UBSM BK-KO cells were depolarized with approximately 12 mV. Isoproterenol, a nonspecific beta-AR agonist, and forskolin, an adenylate cyclase activator, decreased phasic and tonic contractions of WT UBSM strips in a concentration-dependent manner. In the presence of IBTX, the concentration-response curves to isoproterenol and forskolin were shifted to the right in WT UBSM strips. Isoproterenol- and forskolin-mediated relaxations were enhanced in BK-KO UBSM strips, and a leftward shift in the concentration-response curves was observed. The leftward shift was eliminated upon PKA inhibition with H-89, suggesting upregulation of the beta-AR-cAMP pathway in BK-KO mice. These results indicate that the BK channel is a key modulator in beta-AR-mediated relaxation of UBSM and further suggest that alterations in BK channel expression or function could contribute to some pathophysiological conditions such as overactive bladder and urinary incontinence.
authors.affiliation: Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Coker Life Sciences Bldg., Rm. 709, 715 Sumter St., Columbia, SC 29208, USA.
authors.forename: Sean M
authors.initials: SM
authors.lastname: Brown
authors.forename: Lilia M
authors.initials: LM
authors.lastname: Bentcheva-Petkova
authors.forename: Lei
authors.initials: L
authors.lastname: Liu
authors.forename: Kiril L
authors.initials: KL
authors.lastname: Hristov
authors.forename: Muyan
authors.initials: M
authors.lastname: Chen
authors.forename: Whitney F
authors.initials: WF
authors.lastname: Kellett
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Meredith
authors.forename: Richard W
authors.initials: RW
authors.lastname: Aldrich
authors.forename: Mark T
authors.initials: MT
authors.lastname: Nelson
authors.forename: Georgi V
authors.initials: GV
authors.lastname: Petkov
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D050857:Synaptotagmins; D001743:Urinary Bladder / Q000502:physiology*; D014549:Urinary Incontinence / Q000503:physiopathology
chemical_list: D000318:Adrenergic beta-Agonists; D009419:Nerve Tissue Proteins; D010455:Peptides; D011943:Receptors, Adrenergic, beta; C498723:Syt17 protein, mouse; D050857:Synaptotagmins; D005576:Colforsin; C064719:iberiotoxin; D017868:Cyclic AMP-Dependent Protein Kinases; D007545:Isoproterenol; D002118:Calcium