Different kinases regulate activation of voltage-dependent calcium channels by depolarization in GH3 cells.
The L-type Ca(2+) channel is the primary voltage-dependent Ca(2+)-influx pathway in many excitable and secretory cells, and direct phosphorylation by different kinases is one of the mechanisms involved in the regulation of its activity. The aim of this study was to evaluate the participation of Ser/Thr kinases and tyrosine kinases (TKs) in depolarization-induced Ca(2+) influx in the endocrine somatomammotrope cell line GH3. Intracellular Ca(2+) concentration ([Ca(2+)](i)) was measured using a spectrofluorometric method with fura 2-AM, and 12.5 mM KCl (K(+)) was used as a depolarization stimulus. K(+) induced an abrupt spike (peak) in [Ca(2+)](i) that was abolished in the presence of nifedipine, showing that K(+) enhances [Ca(2+)](i), preferably activating L-type Ca(2+) channels. H89, a selective PKA inhibitor, significantly reduced depolarization-induced Ca(2+) mobilization in a concentration-related manner when it was applied before or after K(+), and okadaic acid, an inhibitor of Ser/Thr phosphatases, which has been shown to regulate PKA-stimulated L-type Ca(2+) channels, increased K(+)-induced Ca(2+) entry. When PKC was activated by PMA, the K(+)-evoked peak in [Ca(2+)](i), as well as the plateau phase, was significantly reduced, and chelerythrine (a PKC inhibitor) potentiated the K(+)-induced increase in [Ca(2+)](i), indicating an inhibitory role of PKC in voltage-dependent Ca(2+) channel (VDCC) activity. Genistein, a TK inhibitor, reduced the K(+)-evoked increase in [Ca(2+)](i), but, unexpectedly, the tyrosine phosphatase inhibitor orthovanadate reduced not only basal Ca(2+) levels but, also, Ca(2+) influx during the plateau phase. Both results suggest that different TKs may act differentially on VDCC activation. Activation of receptor TKs with epidermal growth factor (EGF) or vascular endothelial growth factor potentiated K(+)-induced Ca(2+) influx, and AG-1478 (an EGF receptor inhibitor) decreased it. However, inhibition of the non-receptor TK pp60 c-Src enhanced K(+)-induced Ca(2+) influx. The present study strongly demonstrates that a complex equilibrium among different kinases and phosphatases regulates VDCC activity in the pituitary cell line GH3: PKA and receptor TKs, such as vascular endothelial growth factor receptor and EGF receptor, enhance depolarization-induced Ca(2+) influx, whereas PKC and c-Src have an inhibitory effect. These kinases modulate membrane depolarization and may therefore participate in the regulation of a plethora of intracellular processes, such as hormone secretion, gene expression, protein synthesis, and cell proliferation, in pituitary cells.
Vela
Jorge
J
Instituto de Biología y Medicina Experimental, CONICET, V. Obligado 2490, (1428Buenos Aires, Argentina.
Pérez-Millán
María Inés
MI
Becu-Villalobos
Damasia
D
Díaz-Torga
Graciela
G
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002273:Carcinogens / Q000494:pharmacology; D002460:Cell Line; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism; D005260:Female; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D007546:Isoquinolines / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D010902:Pituitary Gland / Q000166:cytology*; D010911:Pituitary Neoplasms; D011189:Potassium Chloride / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D051381:Rats; D011920:Rats, Inbred WF; D013449:Sulfonamides / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D020746:Calcium Channels, L-Type; D002273:Carcinogens; D005456:Fluorescent Dyes; D007546:Isoquinolines; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; C049925:fura-2-am; D011189:Potassium Chloride; D011494:Protein Kinases; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D016392:Proto-Oncogene Proteins pp60(c-src); D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D016257:Fura-2