Calcium store depletion potentiates a phosphodiesterase inhibitor- and dibutyryl cGMP-evoked calcium influx in rat pituitary GH3 cells.
A role for cGMP in the control of capacitative Ca2+ influx was identified in rat pituitary GH3 cells. Application of 50 microM - 1 mM of the non-specific phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), or the specific cGMP-phosphodiesterase inhibitor, zaprinast, induced a dose-dependent increase in the intracellular free Ca2+ concentration [Ca2+]i of the pituitary cell line, as assessed by video ratio imaging using fura-2. Response onset times were identical and response profiles were similar in all cells analysed. Application of 50 microM dibutyryl cGMP to GH3 cells resulted in heterogeneous Ca2+ responses, consisting of single or multiple transients with varying onset times. In all cases, increases in [Ca2+]i were predominantly due to Ca2+ influx, since no responses were detected in low Ca2+ medium, or following pre-incubation of cells with 1 microM verapamil, or nicardipine. Depleting intracellular Ca2+ stores by prior treatment of cells with 1 microM thapsigargin resulted in a dramatic potentiation in the Ca2+ influx mediated by both phosphodiesterase inhibitors and dibutyryl cGMP, suggesting that cGMP modulates a dihydropyridine-sensitive Ca2+ entry mechanism in GH3 cells which is possibly regulated by the state of filling of Ca2+ stores.
Willmott
N J
NJ
University Department of Pharmacology, Oxford, UK.
Asselin
J
J
Galione
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D003995:Dibutyryl Cyclic GMP / Q000378:metabolism*; D004095:Dihydropyridines / Q000378:metabolism / Q000494:pharmacology; D009712:Nucleotides, Cyclic / Q000378:metabolism / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000378:metabolism / Q000494:pharmacology; D010902:Pituitary Gland / Q000378:metabolism*; D051381:Rats; D013729:Terpenes / Q000378:metabolism / Q000494:pharmacology; D019284:Thapsigargin
D015220:Calcium Channels; D004095:Dihydropyridines; D009712:Nucleotides, Cyclic; D010726:Phosphodiesterase Inhibitors; D013729:Terpenes; D003995:Dibutyryl Cyclic GMP; D019284:Thapsigargin; C038806:1,4-dihydropyridine; D002118:Calcium