SODIUM-INDUCED CALCIUM RELEASE FROM MITOCHONDRIA IN BROWN ADIPOSE-TISSUE

Coupled mitochondria of brown adipose tissue can accumulate Ca2(+) if a substrate is present. The Ca2(+) is released by addition of 20 mM Na(+), but not by addition of K(+) or choline(+). Energy-dissipating Na(+)-induced Ca2(+) cycling occurs maximally with 20 mM Na(+) and 10 μM Ca2(+). In brown adipocytes, the Ca2(+) ionophore A23187 and the Na(+) ionophore monensin increase respiration if substrate is added, and incubation in a low-Na(+) buffer decreases norepinephrine-induced respiration. Thus Na(+)-induced Ca2(+) release takes place in brown adipose tissue; released Ca2(+) could have a regulatory or thermogenic role or both.