Evidence for a phorbol ester-insensitive phosphorylation step in capacitative calcium entry in rat thymic lymphocytes.
Experiments were undertaken to investigate the regulation of capacitative Ca2+ entry by phorbol ester-sensitive protein kinase C and serine/threonine protein phosphatase activity. The thapsigargin-activated Ca2+ entry pathway was probed in control cells and cells treated with phosphatase type 1/2A inhibitors, okadaic acid and calyculin A, or with the phorbol ester, phorbol 12-myristate 13-acetate. The permeability state of this pathway was monitored in the presence or absence of these agents using fluorometric measurements of intracellular Ca2+ concentration, unidirectional Mn2+ entry, and membrane potential and unidirectional measurements of Ca2+ uptake using 45Ca2+. The results of these studies demonstrate that modification of the phosphorylation state of target protein(s) on serine/threonine amino acid residues by inhibition of phosphatase type 1/2A inhibits the capacitative Ca2+ entry pathway in rat thymic lymphocytes. Importantly, the capacitative Ca2+ entry pathway in rat thymic lymphocytes is not modulated by activation of phorbol ester-sensitive protein kinase C.
Marriott
I
I
Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA.
Mason
M J
MJ
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017136:Ion Transport; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008387:Marine Toxins; D019319:Okadaic Acid / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D019284:Thapsigargin / Q000494:pharmacology; D013950:Thymus Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
D004791:Enzyme Inhibitors; D008387:Marine Toxins; D010080:Oxazoles; D019319:Okadaic Acid; D019284:Thapsigargin; C059041:calyculin A; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium