AJP - Endocrinology and Metabolism, Vol 251, Issue 2 192-E195, Copyright © 1986 by American Physiological Society
Rapid changes in number of GDP binding sites on brown adipose tissue mitochondria
A. G. Swick and R. W. Swick
GDP binding to brown adipose tissue (BAT) mitochondria increased more than
twofold in 20 min when rats were moved from 27 to 4 degrees C. When animals
housed at 4 degrees C for 2 h were returned to 27 degrees C, GDP binding
decreased sharply in 20 min and returned to control levels in 2 h. These
results are consistent with a rapid unmasking and remasking of GDP binding
sites. GDP binding to mitochondria from warm and acutely cold treated rats
was not modified by prior swelling, by freeze-thawing, nor by sonication of
the mitochondria before assay. GDP-inhibitable proton conductance, as
measured by passive swelling, was unaffected by this brief exposure to cold
but more than doubled in rats kept at 4 degrees C for 10 days. We
hypothesize that the rate of GDP-inhibitable swelling may be a reflection
of uncoupling protein concentration in the BAT mitochondria, whereas
physiological thermogenic activity is more appropriately indicated by GDP
binding. The alterations in binding activity appear not to be due to
changes in the mitochondrial membrane integrity.
