Intracellular Ca2+ pools in PC12 cells. A unique, rapidly exchanging pool is sensitive to both inositol 1,4,5-trisphosphate and caffeine-ryanodine.
Release of Ca2+ from intracellular stores was studied in the parent PC12 cell line and in recently isolated clones sensitive or insensitive to caffeine. In the caffeine-sensitive cells the cytosolic free Ca2+ concentration ([Ca2+]i) responses by the xanthine drug and by stimulants of receptors coupled to inositol 1,4,5-trisphosphate (Ins-P3) generation (bradykinin, ATP) depend on separate pathways because 1) caffeine does not stimulate the hydrolysis of phosphatidylinositol 4,5-bisphosphate and 2) Ca(2+)-induced Ca2+ release, the process activated by caffeine, plays no major role in the Ins-P3-induced Ca2+ mobilization. Although distinct, these two mechanisms converge onto the same Ca2+ store. In fact 1) the [Ca2+]i responses by receptor agonists and caffeine were not additive; 2) either type of agent reduced (up to complete inhibition) the response to a subsequent administration of the same or the other agent; 3) all these responses were prevented by selective Ca2+ ATPase blockers; 4) ryanodine, which affects the intracellular Ca2+ channel sensitive to caffeine, also induced depletion of the receptor-sensitive Ca2+ pool; 5) in the 10 PC12 clones tested, sensitivity to caffeine paralleled ryanodine sensitivity. Therefore, PC12 cells, similar to some smooth muscle fibers but at variance with neurons and other secretory cells, express a single, rapidly exchanging Ca2+ store in which two distinct intracellular Ca2+ channels, i.e. the receptors for caffeine-ryanodine and Ins-P3, appear to be colocalized.
Zacchetti
D
D
Department of Pharmacology, Scientific Institute San Raffaele, University of Milano, Italy.
Clementi
E
E
Fasolato
C
C
Lorenzon
P
P
Zottini
M
M
Grohovaz
F
F
Fumagalli
G
G
Pozzan
T
T
Meldolesi
J
J
D000634:Aminoquinolines; D001920:Bradykinin / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D006868:Hydrolysis; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology*
D000634:Aminoquinolines; D004075:Diglycerides; D005456:Fluorescent Dyes; D012433:Ryanodine; D002110:Caffeine; D015759:Ionomycin; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D000252:Calcium-Transporting ATPases; C035739:Quin2; D001920:Bradykinin; D002118:Calcium; D016257:Fura-2