The role of caffeine-sensitive Ca2+ stores in agonist- and inositol 1,4,5-trisphosphate-induced Ca2+ release from bovine adrenal chromaffin cells.
In single bovine adrenal chromaffin cells loaded with fura-2, histamine, angiotensin II (AII) and caffeine elicited large transient increases of intracellular free Ca2+ concentration [( Ca2+]i) in the absence of external Ca2+, with peak amplitudes averaging 726 +/- 138 (n = 14), 710 +/- 102 (n = 21) and 830 +/- 100 nM (n = 30) respectively. A substantial portion of the agonist-induced rise in [Ca2+]i depended on Ca2+ release from caffeine-sensitive stores, as pretreatment with caffeine diminished subsequent agonist responses by 90-95%. Conversely, pretreatment with histamine or AII decreased subsequent caffeine responses by 100% and 90% respectively. The effects of caffeine most likely resulted from activation of a Ca(2+)-induced Ca(2+)-release (CICR) process, whereas histamine and AII initially acted through generation of Ins(1,4,5)P3. The relationship of Ins(1,4,5)P3- and caffeine-sensitive Ca2+ pools was studied by using alpha-toxin-permeabilized chromaffin cells. Evidence was found for three non-mitochondrial, ATP-dependent, Ca2+ pools: one exclusively sensitive to Ins(1,4,5)P3 (pool 1), a second sensitive to both Ins(1,4,5)P3 and caffeine (pool 2), and a third exclusively sensitive to caffeine (pool 3). The existence of pools 1 and 3, and the ability of agonists such as histamine to discharge pool 3 completely, supports a two-pool model in which a caffeine-sensitive CICR mechanism plays a major role in the generation of agonist-induced Ca2+ spikes in bovine chromaffin cells.
Stauderman
K A
KA
Marion Merrell Dow Research Institute, Cincinnati, OH 45215.
McKinney
R A
RA
Murawsky
M M
MM
D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism*; D000804:Angiotensin II / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002417:Cattle; D002463:Cell Membrane Permeability; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D006632:Histamine / Q000008:administration & dosage / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology
D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D000804:Angiotensin II; D012433:Ryanodine; D002110:Caffeine; D006632:Histamine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium; D016257:Fura-2