Growth hormone increases ca2+ uptake in rat fat cells by a
mechanism dependent on protein kinase c1,2.
Gaur, Shikha, Hiroshi Yamaguchi, and H. Maurice Goodman.
Department of Physiology, University of Massachusetts Medical
School, Worcester, Massachusetts, 01655, Phone: 508 856 2101; Fax:
508 856 5997
APStracts 2:0400C, 1995.
GH (500 ng/ml) rapidly doubled intracellular free Ca2+ concentration
([Ca2+]i) in rat adipocytes as determined with the Ca2+ indicator
fura-2. No response was seen in Ca2+-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 mM K+ also increased [Ca2+]i, and the increase
in [Ca2+]i due to either GH or 30 mM K+ 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 (DAG) analog, sn-1,2 dioctanoyl
-glycerol (50 [mu]M), duplicated and the protein kinase C(PKC)
inhibtors calphostin C (100 nM), chelerythrine (1 [mu]M), and
bisindolylmaleimide (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 Ca2+
-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.
Received 16 June 1995; accepted in final form 24 October 1995.
APS Manuscript Number C349-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95