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Am J Physiol Cell Physiol 270: C1478-C1484, 1996;
0363-6143/96 $5.00
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AJP - Cell Physiology, Vol 270, Issue 5 C1478-C1484, Copyright © 1996 by American Physiological Society

ARTICLES

Growth hormone regulates cytosolic free calcium in rat fat cells by maintaining L-type calcium channels

S. Gaur, H. Yamaguchi and H. M. Goodman
Department of Physiology, University of Massachusetts Medical School, Worcester 01655, USA.

In freshly isolated individual rat adipocytes, cytosolic free Ca2+ concentration ([Ca2+]i) as measured with fura 2 slowly declined during incubation but was sustained, or even somewhat increased, by brief treatment with growth hormone (GH) at the beginning of a 3-h incubation period. GH-treated adipocytes were more permeable to Ca2+ than GH-deprived cells as indicated, using Mn2- as a surrogate and monitoring influx by the rate of quenching of fura 2 fluorescence. Blockage of Ca2- channels with 100 nM nimodipine lowered [Ca2+]i in GH-treated cells to the level seen in GH-deprived cells. Increases in [Ca2+]i or the rate of Mn2+ entry were twofold greater in GH-treated than in GH-deprived cells when extracellular K+ was increased to 30 mM. Similarly, the Ca2+ channel agonist BAY K 5552 or the diacylglycerol analogue 1,2-dioctanoyl-sn-glycerol increased [Ca2+]i more in GH-treated than in GH-deprived adipocytes. Ca(2+)-ATPase activity was two times higher in plasma membranes isolated from GH-treated than from GH-deprived cells. Continued synthesis of Ca(2+)-ATPase may depend on [Ca2+]i, since the effects of GH on [Ca2+]i and Ca(2+)-ATPase were blocked by a cycloheximide or verapamil. We suggest that voltage-sensitive L-type Ca2+ channels regulate steady-state [Ca2+]i in rat adipocytes and that GH maintains the number or functional integrity of these channels.


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S. Gaur, M. E. Morton, G. P. Frick, and H. M. Goodman
Growth hormone regulates the distribution of L-type calcium channels in rat adipocyte membranes
Am J Physiol Cell Physiol, August 1, 1998; 275(2): C505 - C514.
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Rapid Ca2+ Influx and Diacylglycerol Synthesis in Growth Hormone-mediated Islet beta -Cell Mitogenesis
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