Calcium oscillations in parotid acinar cells induced by microsomal Ca(2+)-ATPase inhibition.
Previous studies have demonstrated in single rat parotid acinar cells that the microsomal Ca(2+)-ATPase inhibitor thapsigargin mobilizes Ca2+ specifically from the inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ store, activates plasma membrane Ca2+ permeability, and induces intracellular Ca2+ concentration ([Ca2+]i) oscillations that are quite similar to those activated by carbachol. Nevertheless, the IP3-sensitive Ca2+ store remains continuously depleted during thapsigargin-induced oscillations, indicating that this pool is not involved in the oscillation mechanism. To determine the specificity of thapsigargin's effects, in the present study we have examined the effects on [Ca2+]i in single rat parotid acinar cells of two other microsomal Ca(2+)-ATPase inhibitors, cyclopiazonic acid (CPA) and 2,5-di-tert-butyl-1,4-benzohydroquinone (BHQ), and compared them with the effects of thapsigargin in the same cells. Our results demonstrate that thapsigargin, CPA, and BHQ all similarly deplete the IP3-sensitive Ca2+ store specifically, activate plasma membrane Ca2+ influx, and induce [Ca2+]i oscillations, strongly suggesting that these agents have a specific inhibitory action on microsomal Ca(2+)-ATPase activity. BHQ, in addition, inhibits plasma membrane Ca2+ influx. The data lend strong support to a model in which the state of Ca2+ filling of the IP3-sensitive store regulates plasma membrane Ca2+ influx. These results suggest either that a Ca2+ pump is involved which is insensitive to structurally dissimilar inhibitors or that a Ca2+ pump is not involved in refilling of the Ca2+ pool involved in [Ca2+]i oscillations in these cells.
Foskett
J K
JK
Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada.
Wong
D
D
D000818:Animals; D016227:Benzoquinones / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D016257:Fura-2; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D010306:Parotid Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D016227:Benzoquinones; D007211:Indoles; D013729:Terpenes; C067344:2,5-di-tert-butylbenzoquinone; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2; C000543:cyclopiazonic acid