AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 4 787-R793, Copyright © 1986 by American Physiological Society
K+-H+ exchange and volume homeostasis in brown adipose tissue mitochondria
D. J. DiResta, K. P. Kutschke, M. D. Hottois and K. D. Garlid
K+-H+ exchange activity in hamster brown adipose tissue mitochondria is
activated following depletion of matrix Mg2+ with the divalent cation
ionophore A23187. Quinine inhibits K+-H+ exchange reversibly with an I50 of
22 microM, whereas mild treatment with N,N'-dicyclohexylcarbodiimide (DCCD)
inhibits this activity irreversibly. In an attempt to label and identify
the K+-H+ antiporter protein, brown adipose tissue mitochondria were
incubated with [14C]DCCD and subjected to denaturing polyacrylamide gel
electrophoresis and fluorography. We observed a labeled band of relative
mol wt, 78,000, which satisfies criteria established in rat liver
mitochondria for the identification of this carrier (W. H. Martin et al.,
J. Biol. Chem. 259: 2062-2065, 1984). Thus Mg2+ and quinine each protect
the K+-H+ exchanger against both inhibition and binding by DCCD. Volume
homeostasis in brown adipose tissue mitochondria, as in other mitochondria,
requires a balance between K+ influx and efflux. We propose that regulation
of the K+-H+ antiporter, the primary K+ efflux mechanism, plays a major
role in this process.
