Activation of the sodium pump blocks the growth hormone-induced increase in cytosolic free calcium in rat adipocytes.
GH promptly increases cytosolic free calcium ([Ca2+]i) in freshly isolated rat adipocytes. Adipocytes deprived of GH for 3 h or longer are incapable of increasing [Ca2+]i in response to GH, but instead respond in an insulin-like manner. Insulin blocks the GH-induced increase in [Ca2+]i in GH-replete cells and stimulates the sodium pump (i.e. Na+/K+-ATPase), thereby hyperpolarizing the cell membrane. Blockade of the Na+/K+-ATPase with 100 microM ouabain reversed these effects of insulin and enabled GH to increase [Ca2+]i in GH-deprived adipocytes. Both insulin and GH activated the sodium pump in GH-deprived adipocytes, as indicated by increased uptake of 86Rb+. Decreasing availability of intracellular Na+ by blockade of Na+/K+/ 2Cl- symporters or Na+/H+ antiporters abolished the effects of both hormones on 86Rb+ uptake and enabled both GH and insulin to increase [Ca2+]i in GH-deprived adipocytes. The data suggest that hormonal stimulation of Na+/K+-ATPase activity interferes with activation of voltage-sensitive calcium channels by either membrane hyperpolarization or some unknown interaction between the sodium pump and calcium channels.
Gaur
S
S
Department of Physiology, University of Massachusetts Medical School, Worcester 01655, USA.
Yamaguchi
H
H
Goodman
H M
HM
D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D013006:Growth Hormone / Q000494:pharmacology* / Q000502:physiology; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D009553:Nimodipine / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D012413:Rubidium / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D007328:Insulin; D002034:Bumetanide; D009553:Nimodipine; D010042:Ouabain; D013006:Growth Hormone; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D002118:Calcium