cAMP- and diacylglycerol-mediated pathways elevate cytosolic free calcium concentration via dihydropyridine-sensitive, omega-conotoxin-insensitive calcium channels in normal rat anterior pituitary cells.
The effect of 8-bromocyclic AMP (8-Br-cAMP) and phorbol 12-myristate 13-acetate (PMA), a protein kinase C activator, on cytosolic free calcium concentration ([Ca2+]i) in normal rat anterior pituitary cells was examined. [Ca2+]i was monitored directly by the fluorescent indicator fura-2. 8-Br-cAMP as well as PMA elevated [Ca2+]i in a concentration-dependent manner. Forskolin (10 mumol/l), which activates adenylate cyclase, and 1-oleoyl-2-acetyl-glycerol (10 mumol/l), another activator of protein kinase C, also increased [Ca2+]i. Both the 8-Br-cAMP (2 mmol/l)- and the PMA (100 nmol/l)-induced increase in [Ca2+]i was dependent on the presence of extracellular calcium and could be inhibited by the calcium channel blockers Mg2+ and nifedipine, but not by omega-conotoxin (100 nmol/l). The half-maximally inhibitory concentrations of Mg2+ and nifedipine were about 12 mmol/l and 160 nmol/l, respectively, for the [Ca2+]i response to 8-Br-cAMP (2 mmol/l), and were about 6 mmol/l and 400 nmol/l, respectively, for the PMA (100 nmol/l)-induced increase in [Ca2+]i. The sodium channel blocker tetrodotoxin (5 mumol/l) or PMA (100 nmol/l) on [Ca2+]i. After pretreatment for 3 min with PMA (100 nmol/l), the subsequent K+ (100 mmol/l)- or arachidonic acid (3 mumol/l)-induced increase in [Ca2+]i was decreased by about 50%. By contrast, pretreatment (3 min) with 8-Br-cAMP (2-10 mmol/l) markedly enhanced the subsequent [Ca2+]i response to K+ (100 mmol/l), and left the effect of arachidonic acid (3 mumol/l) on [Ca2+]i unimpaired.(ABSTRACT TRUNCATED AT 250 WORDS)
Schöfl
C
C
Department of Pharmacology, University of Freiburg, Federal Republic of Germany.
Meier
K
K
Götz
D M
DM
Knepel
W
W
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D002132:Calcium Radioisotopes; D000242:Cyclic AMP / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D004075:Diglycerides / Q000378:metabolism*; D004095:Dihydropyridines / Q000494:pharmacology; D005989:Glycerides / Q000378:metabolism*; D008297:Male; D008978:Mollusk Venoms / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013050:Spectrometry, Fluorescence; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D020866:omega-Conotoxin GVIA
D001095:Arachidonic Acids; D015220:Calcium Channels; D002132:Calcium Radioisotopes; D004075:Diglycerides; D004095:Dihydropyridines; D005989:Glycerides; D008978:Mollusk Venoms; D015124:8-Bromo Cyclic Adenosine Monophosphate; D016718:Arachidonic Acid; D020866:omega-Conotoxin GVIA; D000242:Cyclic AMP; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium