title: Control of the mode of excitation-contraction coupling by Ca(2+) stores in bovine trachealis muscle.
abstract: Full muscarinic stimulation in bovine tracheal smooth muscle caused a sustained contraction and increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) that was largely resistant to inhibition by nifedipine. Depletion of internal Ca(2+) stores with cyclopiazonic acid resulted in an increased efficacy of nifedipine to inhibit this contraction and the associated increase in [Ca(2+)](i). Thus internal Ca(2+) store depletion promoted electromechanical coupling between full muscarinic stimulation and muscle contraction to the detriment of pharmacomechanical coupling. A similar change in coupling mode was induced by ryanodine even when it did not significantly modify the initial transient increase in [Ca(2+)](i) induced by this stimulation, indicating that depletion of internal stores was not necessary to induce the change in excitation-contraction coupling mode. Blockade of the Ca(2+)-activated K(+) channel by tetraethylammonium, charybdotoxin, and iberiotoxin all induced the change in excitation-contraction coupling mode. These results suggest that in this preparation, Ca(2+) released from the ryanodine-sensitive Ca(2+) store, by activating Ca(2+)-activated K(+) channels, plays a central role in determining the expression of the pharmacomechanical coupling mode between muscarinic excitation and the Ca(2+) influx necessary for the maintenance of tone.
authors.affiliation: Research Group in Mechanisms of Diseases, Department of Physiology, Faculty of Medicine, The University of Hong Kong, Hong Kong, China SAR.
authors.forename: L
authors.initials: L
authors.lastname: Tao
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
authors.forename: J P
authors.initials: JP
authors.lastname: Bourreau
mesh_terms: D000818:Animals; D018723:Bethanechol / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002417:Cattle; D018999:Charybdotoxin / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D012433:Ryanodine / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects / Q000502:physiology*
chemical_list: D002121:Calcium Channel Blockers; D010455:Peptides; D015221:Potassium Channels; D018723:Bethanechol; D018999:Charybdotoxin; D012433:Ryanodine; D019789:Tetraethylammonium; C064719:iberiotoxin; D009543:Nifedipine; D002118:Calcium