Action of insulin on the na+/k+-atpase and the na+/k+/2cl-
cotransporter in 3t3-l1 adipocytes.
Sargeant, Robert J., Zhi Liu, and Amira Klip.
Division of Cell Biology, The Hospital for Sick Children, Toronto,
Ontario M5G 1X8, Canada
APStracts 2:0080C, 1995.
The Na+/K+-ATPase presents several different isoforms of its [alpha] and
[beta]
subunits. We detected a1 and b1 mRNA transcripts and polypeptides in
3T3-L1 fibroblasts; during differentiation into adipocytes, a1 mRNA
decreased, a2 mRNA was induced, b1 mRNA dropped to undetectable
levels, and b2 was never expressed suggesting that 3T3-L1 adipocytes
may express an unidentified Na+/K+-ATPase [beta] subunit isoform. Insulin
rapidly increased ion pump activity (ouabain-sensitive 86Rb+(K+)
uptake) in 3T3-L1 fibroblasts and adipocytes without changing the
plasma membrane concentration of a1 or a2 subunits as determined by
subcellular membrane fractionation and immunoblotting or by
[3H]ouabain binding to intact cells. Monensin, which raises the
concentration of intracellular Na+, increased Na+/K+-pump activity
and no further stimulation was achieved with insulin. The stimulation
of the pump by insulin was reduced by bumetanide, an inhibitor of the
Na+/K+/2Cl- cotransporter, and was prevented by omission of
extracellular chloride. Insulin increased both ouabain-sensitive and
bumetanide-sensitive 86Rb+(K+) uptake. These results suggest that
insulin-activation of the Na+/K+-ATPase in 3T3-L1 adipocytes is
mediated by an elevation in intracellular Na+ that is likely the
consequence of Na+/K+/2Cl- cotransporter activation.
Received 28 September 1994; accepted in final form 20 January
1995.
APS Manuscript Number C586-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 February 1995.