Muscle fiber type-specific translocation of [alpha]2 and [beta] subunits of the na+-k+-atpase to the plasma membrane induced by insulin. Lavoie, Louis, Denis Roy, Toolsie Ramlal, Luce Dombrowski, Pablo Martin-Vasallo, Andr[acute]e Marette, Jean-Louis Carpentier, and Amira Klip. Division of Cell Biology, The Hospital for Sick Children, Toronto, Ontario, M5G 1X8, Canada; Laval University Hospital Research Centre, Ste-Foy, Quebec, G1V 4G2, Canada; Laboratorio de Biolog[acute]ia del Desarrollo, Departamento de Bioqu[acute]imica y Biolog[acute]ia Molecular, Universidad de La Laguna, Avda Astrof[acute]isico S[acute]anchez s/n, 38206 La Laguna, Tenerife, Spain; and D[acute]epartement de Morphologie, Centre M[acute]edical Universitaire, Universit[acute]e de Gen[grave]eve, CH-1211, Geneva, Switzerland
APStracts 2:0415C, 1995.
We have previously shown that an acute insulin treatment induces redistribution of the [alpha]2 and [beta]1 isoforms of the Na+-K+ -ATPase from intracellular membranes to plasma membranes, detected upon subcellular fractionation of mixed muscles and immunoblotting with isoform-specific antibodies (Hundal et al., J. Biol. Chem. 267: 5040-5043, 1992). In the present study we give both biochemical and morphological evidence that this insulin effect is operative in muscles composed mostly of oxidative (red) fibers but not in muscles composed mostly of glycolytic (white) fibers. The redistribution of the Na+-K+-ATPase [alpha]2 and [beta]1 isoforms after insulin injection was detected in membranes isolated from red muscles (soleus, red gastrocnemius, red rectus femoris and red vastus lateralis) but not in membranes from white muscles (white gastrocnemius, tensor fasciae latae, white rectus femoris and white vastus lateralis). Following insulin injection, the potassium -dependent 3-O-methylfluorescein phosphatase activity of the enzyme was higher by 22% in the plasma membrane-enriched fraction and lower by 15% in the internal membrane fraction isolated from red but not from white muscles. Quantitative immunoelectron microscopy using ultrathin muscle cryosections showed that in vivo insulin stimulation augmented the density of Na+-K+-ATPase [alpha]2 and [beta]1 isoforms at the plasma membrane of soleus muscle by 80% and 124%, respectively, with no change in white gastrocnemius muscle. The effect of insulin to increase the content of Na+-K+-ATPase [alpha]2 and [beta]1 subunits in isolated plasma membranes was still observed when glycemia was prevented from dropping by using hyperinsulinemic -euglycemic clamps. We conclude that the insulin-induced redistribution of the [alpha]2 and [beta]1 isoforms of the Na+-K+ -ATPase from an intracellular pool to the plasma membrane is restricted to oxidative fiber-type skeletal muscles. This may be related to the selective expression of [beta]1 subunits in these fibers, and implies that the [beta]2 subunit, typical of glycolytic muscles, does not sustain translocation of [alpha]2b2 complexes. 

Received 6 July 1995; accepted in final form 6 November 1995.
APS Manuscript Number C406-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95