Receptor-activated Ca2+ influx. Two independently regulated mechanisms of influx stimulation coexist in neurosecretory PC12 cells.
Receptor-activated Ca2+ influx was investigated in PC12 cells clones loaded with fura-2. Cells were stimulated in a Ca(2+)-free medium and studied after reintroduction of the cation or addition of Mn2+ into the medium. A first influx component, independent of receptor activation and sustained by depletion of the intracellular inositol 1,4,5-trisphosphate sensitive Ca2+ store (store-dependent Ca2+ influx, SDCI), was identified by experiments with carbachol followed by atropine and with agents that induce store discharge without polyphosphoinositide hydrolysis: thapsigargin, an inhibitor of Ca(2+)-ATPase activity; ryanodine and caffeine, activators of the ryanodine receptor. A second component of Ca2+ influx, induced by carbachol and rapidly blocked by atropine, relies on receptor-effector coupling via G protein(s) different from that (those) involved in phospholipase C activation. SDCI and receptor-coupled influx are similar in their voltage dependence and insensitivity to forskolin and phorbol esters but they differ with respect to their Mn2+ permeability and their sensitivity to the SC 38249 imidazole blocker. The two components might play different roles. SDCI might act as a safety device to prevent Ca2+ store depletion whereas receptor-dependent influx might control physiological functions such as secretion and growth.
Clementi
E
E
Department of Pharmacology, University of Milano, Italy.
Scheer
H
H
Zacchetti
D
D
Fasolato
C
C
Pozzan
T
T
Meldolesi
J
J
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001920:Bradykinin / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D016257:Fura-2; D007093:Imidazoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D016716:PC12 Cells; D011956:Receptors, Cell Surface / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology; D015398:Signal Transduction; D013729:Terpenes / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019284:Thapsigargin; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007093:Imidazoles; D011956:Receptors, Cell Surface; D013729:Terpenes; D010566:Virulence Factors, Bordetella; D012433:Ryanodine; D002110:Caffeine; D019284:Thapsigargin; D001285:Atropine; C053318:1-(2,3-bis((4-methoxyphenyl)methoxy)propyl)-1H-imidazole; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D000252:Calcium-Transporting ATPases; D013755:Tetradecanoylphorbol Acetate; D001920:Bradykinin; D002118:Calcium; D016257:Fura-2