Growth hormone increases calcium uptake in rat fat cells by a mechanism dependent on protein kinase C.
Growth hormone (GH; 500 ng/ml) rapidly doubled cytosolic free Ca2+ concentration ([Ca2+]i) in rat adipocytes as determined with the Ca2+ indicator fura 2. No response was seen in Ca(2+)-free medium, suggesting that the increase in [Ca2+]i was due to Ca2+ influx. GH also doubled the influx of Mn2- as inferred from the rate of fluorescence quenching. Depolarization with 30 mMK+ also increased [Ca2+]i, and the increase in [Ca2+]i due to either GH or 30 mMK+ was blocked by 100 nM nimodipine, suggesting that GH increases [Ca2+]i by activating voltage-sensitive L-type Ca2+ channels. GH increased [Ca2+]i even when K+ channels were blocked, suggesting that activation of Ca2+ uptake was not secondary to closure of K+ channels and consequent depolarization. A diacylglycerol (PAG) analogue, 1,2-dioctanoyl-sn-glycerol (50 microM), duplicated, and the protein kinase C(PKC) inhibitors calphostin C (100 nM), chelerythrine (1 microM), and bis-indolylmaleimide (250 nM) inhibited the effects of GH on [Ca2+]i. Xanthogenate tricyclodecan-9-yl (D609), a specific inhibitor of phospholipase C(PLC), abolished the increase in [Ca2+]i due to GH but not to DAG. The results suggest that GH increases [Ca2+]i by activation of PLC, release of DAG, and activation of a Ca(2+)-independent isoform of PKC. PKC-catalyzed phosphorylation of either the Ca2+ channels or a protein that regulates them may account for the influx of Ca2+ produced by GH.
Gaur
S
S
Department of Physiology, University of Massachusetts Medical School, Worcester 01655, USA.
Yamaguchi
H
H
Goodman
H M
HM
D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D001952:Bridged-Ring Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004075:Diglycerides / Q000494:pharmacology; D016257:Fura-2; D013006:Growth Hormone / Q000494:pharmacology*; D008297:Male; D008345:Manganese / Q000378:metabolism; D009553:Nimodipine / Q000494:pharmacology; D009636:Norbornanes; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013859:Thiocarbamates; D013871:Thiones / Q000494:pharmacology; D013997:Time Factors; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D001952:Bridged-Ring Compounds; D004075:Diglycerides; D009636:Norbornanes; D013859:Thiocarbamates; D013871:Thiones; C044295:1,2-dioctanoylglycerol; D008345:Manganese; D009553:Nimodipine; C046498:tricyclodecane-9-yl-xanthogenate; D013006:Growth Hormone; D011493:Protein Kinase C; D010738:Type C Phospholipases; D011188:Potassium; D002118:Calcium; D016257:Fura-2