Depletion and refilling of acetylcholine- and caffeine-sensitive Ca++ stores in tracheal myocytes.
We have previously shown that acetylcholine (ACh) induces oscillations in Ca++ and Ca++-activated Cl- currents (Clca) in tracheal myocytes. These oscillations are initiated by Ca++ release from inositol 1,4,5-trisphosphate-sensitive Ca++ stores and maintained by Ca++ influx, in part, through voltage-operated Ca++ channels. In the current study whole-cell Clca was measured in isolated tracheal smooth muscle cells as an index of changes in intracellular Ca++ concentration. We demonstrate that ACh-sensitive Ca++ stores and caffeine-sensitive Ca++ stores and caffeine-sensitive Ca++ stores are functionally linked but are refilled through distinct pathways. Two pathways responsible for replenishing ACh-sensitive Ca++ stores were identified. Ca++ influx through verapamil-sensitive voltage-operated Ca++ channels and Ca++ uptake through cyclopiazonic acid-sensitive Ca++ pumps accounted for 80% of the response. The other 20% of the response was both cyclopiazonic acid- and verapamil-insensitive. In contrast, the refilling of caffeine-sensitive Ca++ stores was not inhibited by 10 microM cyclopiazonic acid or 10 microM verapamil, but was dependent on extracellular Ca++ concentration. However, 0.2 microM thapsigargin, another more potent Ca++ pump inhibitor, completely and irreversibly eliminated ACh-induced transient Clca, whereas it reduced caffeine-induced Clca by 57%. The differences in refilling mechanisms and the functional overlap of ACh- and caffeine-sensitive Ca++ pools suggest that multiple interactive Ca++ stores play an important role in the generation of Ca++ signals in airway smooth muscle cells.
Liu
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Department of Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson, USA.
Farley
J M
JM
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism*; D013552:Swine; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014132:Trachea / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
D007211:Indoles; D013729:Terpenes; D002110:Caffeine; D019284:Thapsigargin; D014700:Verapamil; D000109:Acetylcholine; D002118:Calcium; C000543:cyclopiazonic acid