Cold-induced changes in Ca2+ transport in duckling skeletal muscle mitochondria

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.