title: Mechanism of ACh-induced asynchronous calcium waves and tonic contraction in porcine tracheal muscle bundle.
abstract: Stimulation of the tracheal muscle bundle by acetylcholine (ACh) results in the generation of asynchronous repetitive Ca2+ waves (ACW) in intact tracheal smooth muscle (TSM) cells. We showed previously that ACW underlie cholinergic excitation-contraction coupling in porcine TSM and that Ca2+ entry through the L-type voltage-gated Ca2+ channel (VGCC) contributes partially to maintenance of the ACW. However, the mechanism of the ACW remains undefined. In this study, we pharmacologically characterized the mechanism of ACh-induced ACW in the intact porcine tracheal muscle bundle. We found that inhibition of receptor-operated channels/store-operated channels (ROC/SOC) by SKF-96365 completely abolished the nifedipine-insensitive component of ACh-mediated ACW and tonic contraction. Blockade of Na+/Ca2+ exchange with KB-R7943 or 2',4'-dichlorobenzamil or removal of extracellular Na+ resulted in nearly complete inhibition of the nifedipine-insensitive component of ACh-mediated ACW and tonic contraction. Inhibition of the sarco(endo)plasmic reticulum Ca2+-ATPase by cyclopiazonic acid abolished the ongoing ACW. Application of 2-aminoethoxydiphenyl borate (2-APB) or xestospongin C to inhibit the inositol 1,4,5-trisphosphate-sensitive sarcoplasmic reticulum (SR) Ca2+ release channels produced no effect on ACh-mediated ACW and tonic contraction. However, pretreatment with caffeine or ryanodine inhibited ACh-induced ACW. Furthermore, application of procaine or tetracaine prevented the generation and abolished the ongoing ACh-mediated ACW and tonic contraction. Collectively, these results indicate that the ACh-stimulated ACW in porcine TSM are produced by repetitive cycles of Ca2+ release from SR through 2-APB- and xestospongin C-insensitive Ca2+ release channels, and plasmalemmal Ca2+ entry involving reverse-mode Na+/Ca2+ exchange, ROC/SOC, and L-type VGCC is required to refill the SR via SERCA to support the ongoing ACW.
authors.affiliation: The James Hogg iCAPTURE Center, Univ. of British Columbia, St. Paul's Hospital, Rm. 292, 1081 Burrard St., Vancouver, BC, Canada V6Z 1Y6.
authors.forename: Jiazhen M
authors.initials: JM
authors.lastname: Dai
authors.forename: Kuo-Hsing
authors.initials: KH
authors.lastname: Kuo
authors.forename: Joyce M
authors.initials: JM
authors.lastname: Leo
authors.forename: Cornelis
authors.initials: C
authors.lastname: van Breemen
authors.forename: Cheng-Han
authors.initials: CH
authors.lastname: Lee
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D012964:Sodium / Q000378:metabolism; D013552:Swine; D014132:Trachea / Q000187:drug effects*
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D000697:Central Nervous System Stimulants; D004791:Enzyme Inhibitors; D007093:Imidazoles; D007211:Indoles; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D012964:Sodium; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D009543:Nifedipine; D000109:Acetylcholine; D002118:Calcium; C000543:cyclopiazonic acid