Mechanisms of activated Ca2+ entry in the rat pancreatoma cell line, AR4-2J.
The characteristics of Ca2+ entry activated by surface receptor agonists and membrane depolarization were studied in the rat pancreatoma cell line, AR4-2J. Ca2+ mobilization activated by substance P, bombesin, or muscarinic receptor stimulation was found to involve both Ca2+ release and entry. In addition, depolarization of the surface membrane of AR4-2J cells with elevated concentrations of K+ activated Ca2+ entry. Ca2+ entry induced by membrane depolarization was inhibited by the L-channel antagonist, nimodipine, while that due to surface receptor agonists was not inhibited by this agent. The microsomal Ca(2+)-ATPase inhibitor, thapsigargin, caused both depletion of the agonist-sensitive intracellular Ca2+ pool and sustained Ca2+ influx indistinguishable from that produced by bombesin or methacholine. These results confirm that, unlike the pancreatic acinar cells from which they are presumably derived, AR4-2J cells express voltage-sensitive, dihydropyridine-inhibitable Ca2+ channels. However, in contrast to previous reports with this cell line, in the AR4-2J cells in use in our laboratory, and under our experimental conditions, surface receptor agonists (including substance P) do not cause Ca2+ influx through voltage-sensitive Ca2+ channels. Instead, we conclude that agonist-activated Ca2+ mobilization is initiated by (1,4,5)IP3-mediated intracellular Ca2+ release and that Ca2+ influx is regulated primarily, if not exclusively, by the state of depletion of the (1,4,5)IP3-sensitive intracellular Ca2+ pool.
Calcium Regulation Section, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina.
G S
GS
Bird
H
H
Takemura
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O
Thastrup
J W
JW
Putney
F S
FS
Menniti
D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016257:Fura-2; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D016210:Methacholine Chloride / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects*; D013373:Substance P / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014407:Tumor Cells, Cultured / Q000378:metabolism
D015220:Calcium Channels; D013729:Terpenes; D016210:Methacholine Chloride; D013373:Substance P; D009553:Nimodipine; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000252:Calcium-Transporting ATPases; D001839:Bombesin; D002118:Calcium; D016257:Fura-2