The caffeine- and ryanodine-sensitive Ca++ store in porcine myometrial cells: its heterogeneity of all-or-none Ca++ release.
The mechanisms for Ca++ release from caffeine-sensitive stores were investigated in freshly dispersed porcine myometrial cells utilizing the fura-2 method. Because the caffeine-sensitive Ca++ store has not been detected in myometrium of mammals, we first determined the existence of this type of store in porcine myometrial cells. The evidence includes: 1) caffeine (1-33 mM)-induced concentration-dependent increase in the intracellular Ca++ concentration ([Ca++]i) in both the presence and absence of extracellular Ca++ and 2) although ryanodine alone (< or = 10 microM) failed to change [Ca++]i, it inhibited the response to caffeine in a use-, concentration- and time-dependent manner. In the cell suspension study, the amount of Ca++ released by 10 mM caffeine was found to be inversely proportional to the amount released by preadministration of caffeine (1-33 mM). In the single cell study, about 30% of cells responded to only a certain concentration of caffeine and the others responded to caffeine gradually. Thapsigargin, an inhibitor of Ca(++)-adenosine triphosphatase in sarcoplasmic reticulum, failed to increase [Ca++]i. Pretreatment with thapsigargin inhibited the response to caffeine in a time- and concentration-dependent manner. These results suggest that in porcine myometrial cells: 1) the Ca++ released from the caffeine- and ryanodine-sensitive store is in an all-or-none manner through compartments of stores or the entire store of a cell and 2) the release process is regulated by luminal Ca++ content of the stores.
Department of Veterinary Physiology and Pharmacology, Iowa State University, Ames, USA.
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D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D009215:Myometrium / Q000187:drug effects* / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology*; D013552:Swine; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D004791:Enzyme Inhibitors; D013729:Terpenes; D012433:Ryanodine; D002110:Caffeine; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium