title: Large-conductance voltage- and Ca2+-activated K+ channels regulate human detrusor smooth muscle function.
abstract: The large-conductance voltage- and Ca(2+)-activated K(+) (BK) channel is expressed in many smooth muscle types, but its role in human detrusor smooth muscle (DSM) is unclear. With a multidisciplinary approach spanning channel molecules, single-channel activity, freshly isolated human DSM cells, intact DSM preparations, and the BK channel specific inhibitor iberiotoxin, we elucidated human DSM BK channel function and regulation. Native human DSM tissues were obtained during open surgeries from patients with no preoperative history of overactive bladder. RT-PCR experiments on single human DSM cells showed mRNA expression of BK channel α-, β(1)-, and β(4)-subunits. Western blot and immunocytochemistry confirmed BK channel α, β(1), and β(4) protein expression. Native human BK channel properties were described using the perforated whole cell configuration of the patch-clamp technique. In freshly isolated human DSM cells, BK channel blockade with iberiotoxin inhibited a significant portion of the total voltage step-induced whole cell K(+) current. From single BK channel recordings, human BK channel conductance was calculated to be 136 pS. Voltage-dependent iberiotoxin- and ryanodine-sensitive transient BK currents were identified in human DSM cells. In current-clamp mode, iberiotoxin inhibited the hyperpolarizing membrane potential transients and depolarized the cell resting membrane potential. Isometric DSM tension recordings revealed that BK channels principally control the contractions of isolated human DSM strips. Collectively, our results indicate that BK channels are fundamental regulators of DSM excitability and contractility and may represent new targets for pharmacological or genetic control of urinary bladder function in humans.
authors.affiliation: Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, 29208, USA.
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: Eric S
authors.initials: ES
authors.lastname: Rovner
authors.forename: Georgi V
authors.initials: GV
authors.lastname: Petkov
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002478:Cells, Cultured; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000235:genetics / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D021122:Protein Subunits; D046509:Tissue Culture Techniques; D014118:Toxins, Biological / Q000494:pharmacology
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels; D010455:Peptides; D021122:Protein Subunits; D014118:Toxins, Biological; C064719:iberiotoxin