title: Functional link between muscarinic receptors and large-conductance Ca2+ -activated K+ channels in freshly isolated human detrusor smooth muscle cells.
abstract: Activation of muscarinic acetylcholine receptors (mAChRs) constitutes the primary mechanism for enhancing excitability and contractility of human detrusor smooth muscle (DSM). Since the large-conductance Ca(2+)-activated K(+) (KCa1.1) channels are key regulators of human DSM function, we investigated whether mAChR activation increases human DSM excitability by inhibiting KCa1.1 channels. We used the mAChR agonist, carbachol, to determine the changes in KCa1.1 channel activity upon mAChR activation in freshly isolated human DSM cells obtained from open bladder surgeries using the perforated whole cell and single KCa1.1 channel patch-clamp recordings. Human DSM cells were collected from 29 patients (23 males and 6 females, average age of 65.9 ± 1.5 years). Carbachol inhibited the amplitude and frequency of KCa1.1 channel-mediated spontaneous transient outward currents and spontaneous transient hyperpolarizations, which are triggered by the release of Ca(2+) from ryanodine receptors. Carbachol also caused membrane potential depolarization, which was not observed in the presence of iberiotoxin, a KCa1.1 channel inhibitor, indicating the critical role of the KCa1.1 channels. The potential direct carbachol effects on KCa1.1 channels were examined under conditions of removing the major cellular Ca(2+) sources for KCa1.1 channel activation with pharmacological inhibitors (thapsigargin, ryanodine, and nifedipine). In the presence of these inhibitors, carbachol did not affect the single KCa1.1 channel open probability and mean KCa1.1 channel conductance (cell-attached configuration) or depolarization-induced whole cell steady-state KCa1.1 currents. The data support the concept that mAChR activation triggers indirect functional KCa1.1 channel inhibition mediated by intracellular Ca(2+), thus increasing the excitability in human DSM cells.
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, USA.
authors.forename: Shankar P
authors.initials: SP
authors.lastname: Parajuli
authors.forename: Kiril L
authors.initials: KL
authors.lastname: Hristov
authors.forename: Qiuping
authors.initials: Q
authors.lastname: Cheng
authors.forename: John
authors.initials: J
authors.lastname: Malysz
authors.forename: Eric S
authors.initials: ES
authors.lastname: Rovner
authors.forename: Georgi V
authors.initials: GV
authors.lastname: Petkov
mesh_terms: D000200:Action Potentials; D000368:Aged; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D005260:Female; D006801:Humans; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D010455:Peptides / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D001743:Urinary Bladder / Q000166:cytology / Q000378:metabolism*
chemical_list: D018679:Cholinergic Agonists; C494841:KCNMA1 protein, human; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D010455:Peptides; D026902:Potassium Channel Blockers; D011976:Receptors, Muscarinic; D019837:Ryanodine Receptor Calcium Release Channel; C064719:iberiotoxin; D002217:Carbachol; D002118:Calcium