Calcium regulation in the myometrium of pregnant sheep

Fractionation of pregnant sheep myometrium has been carried out and the fractions obtained analysed for their marker enzyme content and Ca2+ transporting properties. A fairly pure mitochondrial fraction and a very pure plasma membrane fraction were obtained. Both fractions could accumulate Ca2+ in the presence of ATP but the mechanisms were different, mitochondrial uptake had a high capacity and was inhibited by azide. Plasma membrane uptake was of low capacity and unaffected by azide. The effect of oxalate on plasma membrane suggests that there is an outwardly directed Ca2+ pump in the myometrial cell membrane. Both mitochondria and plasma membrane may be important in the Cas2+ accumulation of relaxation in this muscle.