Growth hormone regulates cytosolic free calcium in rat fat cells by maintaining L-type calcium channels.
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.
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; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism*; D013006:Growth Hormone / Q000494:pharmacology*; D008297:Male; D008345:Manganese / Q000378:metabolism; D009553:Nimodipine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014700:Verapamil / Q000494:pharmacology
D015220:Calcium Channels; D008345:Manganese; D009553:Nimodipine; D013006:Growth Hormone; D003513:Cycloheximide; D014700:Verapamil; D002118:Calcium