AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 6 1046-R1054, Copyright © 1987 by American Physiological Society
Cold-induced changes in Ca2+ transport in duckling skeletal muscle mitochondria
H. Barre and J. Nedergaard
Intermyofibrillar mitochondria were isolated from skeletal muscle
(gastrocnemius) of cold-acclimated (4 degrees C) or control (30 degrees C)
4-wk-old ducklings. Ca2+ transport in the mitochondria was studied with the
Ca2+-sensitive dye arsenazo III. The mitochondria actively took up Ca2+ but
at a lower rate in mitochondria from cold-acclimated than from control
ducklings. After addition of the Ca2+ uptake inhibitor ruthenium red, a low
rate of Ca2+ release was revealed; this rate was, however, higher in the
cold-acclimated than in the control ducklings. Furthermore, these
nonmammalian mitochondria were also found to possess a mechanism for
Na+-stimulated Ca2+ efflux. This mechanism was specific for Na+ (no effects
with choline+ or K+, a small effect with Li+). The effect was maximal with
20 mM Na+, which led to a fourfold increase in rate of Ca2+ efflux. Cold
acclimation led to a doubling of the rate of this Na+-stimulated Ca2+
release. Due to these alterations in Ca2+ fluxes caused by cold
acclimation, the resultant free extramitochondrial Ca2+ levels were higher
in mitochondria from cold-acclimated than from control ducklings. The basal
level was doubled (from 0.26 to 0.50 microM) as was the increase in
steady-state level caused by 10 mM Na+ (from +0.4 to +0.8 microM). The
significance of these alterations for acclimation to cold is discussed.
