Quantal Ca2+ mobilization by ryanodine receptors is due to all-or-none release from functionally discrete intracellular stores.
Low caffeine concentrations were unable to completely release the caffeine- and ryanodine-sensitive intracellular Ca2+ pool in intact adrenal chromaffin cells. This 'quantal' Ca2+ release is the same as that previously observed with inositol Ins(1,4,5)P3-induced Ca2+ release. The molecular mechanism underlying quantal Ca2+ release from the ryanodine receptor was investigated using fura-2 imaging of single chromaffin cells. Our data indicate that the intracellular caffeine-sensitive Ca2+ pool is composed of functionally discrete stores, that possess heterogeneous sensitivities to caffeine. These stores are mobilized by caffeine in a concentration-dependent fashion, and, when stimulated, individual stores release their Ca2+ in an 'all-or-none' manner. Such quantal Ca2+ release may be responsible for graded Ca2+ responses in single cells.
Cheek
T R
TR
Department of Zoology, University of Cambridge, U.K.
Berridge
M J
MJ
Moreton
R B
RB
Stauderman
K A
KA
Murawsky
M M
MM
Bootman
M D
MD
D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002417:Cattle; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D009124:Muscle Proteins / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel
D015220:Calcium Channels; D005456:Fluorescent Dyes; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium; D016257:Fura-2