title: Regulation of urinary bladder smooth muscle contractions by ryanodine receptors and BK and SK channels.
abstract: This study examines the roles of voltage-dependent Ca(2+) channels (VDCC), ryanodine receptors (RyRs), large-conductance Ca(2+)-activated K(+) (BK) channels, and small-conductance Ca(2+)-activated K(+) (SK) channels in the regulation of phasic contractions of guinea pig urinary bladder smooth muscle (UBSM). Nisoldipine (100 nM), a dihydropyridine inhibitor of VDCC, abolished spontaneous UBSM contractions. Ryanodine (10 microM) increased contraction frequency and thereby integrated force and, in the presence of the SK blocker apamin, had a greater effect on integrated force than ryanodine alone. Blocking BK (iberiotoxin, 100 nM) or SK (apamin, 100 nM) channels increased contraction amplitude and duration but decreased frequency. The contractile response to iberiotoxin was more pronounced than to apamin. The increases in contraction amplitude and duration to apamin were substantially augmented with ryanodine pretreatment. These results indicate that BK and SK channels have prominent roles as negative feedback elements to limit UBSM contraction amplitude and duration. RyRs also appear to play a significant role as a negative feedback regulator of contraction frequency and duration, and this role is influenced by the activity of SK channels.
authors.affiliation: Department of Molecular Physiology and Biophysics, University of Vermont College of Medicine, Burlington, Vermont 05405, USA. herrera@salus.med.uvm.edu
authors.forename: G M
authors.initials: GM
authors.lastname: Herrera
authors.forename: T J
authors.initials: TJ
authors.lastname: Heppner
authors.forename: M T
authors.initials: MT
authors.lastname: Nelson
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D004558:Electric Stimulation; D006168:Guinea Pigs; D066298:In Vitro Techniques; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000378:metabolism*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D017981:Receptors, Neurotransmitter / Q000037:antagonists & inhibitors; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D051640:Small-Conductance Calcium-Activated Potassium Channels; D001743:Urinary Bladder / Q000378:metabolism*
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D017981:Receptors, Neurotransmitter; D019837:Ryanodine Receptor Calcium Release Channel; D051640:Small-Conductance Calcium-Activated Potassium Channels; D002118:Calcium