Two distinct pathways for refilling Ca2+ stores in permeabilized bovine trachealis muscle.
Calcium entry from extracellular space to acetylcholine (ACh)-sensitive internal stores was investigated in beta-escin permeabilized bovine tracheal smooth muscle. Cyclopiazonic acid (CPA), a selective inhibitor of the sarcoplasmic reticulum (SR) calcium pump, and nifedipine, both inhibited the refilling, and inhibition was larger when these compounds were used simultaneously. BayK 8644 enhanced the refilling and completely reversed the inhibition induced by cyclopiazonic acid. In pCa 7 solution containing CPA, there was a spontaneous time-dependent decrease of ACh-induced transient contraction. In the presence of nifedipine or verapamil in the incubation solution reduced this time-dependent decrease in contractile responses to ACh stimulation, suggesting that these calcium-entry blockers decreased calcium leakage from internal stores to the extracellular space. These results suggest that in addition to the active calcium uptake in the SR, another pathway controlled by an L-type like calcium channel (dihydropyridine-sensitive) may exist between the extracellular compartment and the lumen of the SR in airway smooth muscle, and contributes significantly to the loading of ACh-sensitive calcium stores.
Qian
Y
Y
Physiology Department, Faculty of Medicine, The University of Hong Kong, SAR China.
Bourreau
J P
JP
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002417:Cattle; D002463:Cell Membrane Permeability / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004928:Escin / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D014132:Trachea / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D007211:Indoles; D004928:Escin; D014700:Verapamil; D000252:Calcium-Transporting ATPases; D009543:Nifedipine; D000109:Acetylcholine; D002118:Calcium; C000543:cyclopiazonic acid