The role of sarcolemma and mitochondria in regulating Ca2+ movements in human myometrium

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Abstract
A subcellular fraction enriched in sarcolemma was isolated by differential and sucrose gradient centrifugation from human myometrium. The Ca2+ binding characteristics of this fraction were compared to that of mitochondria and microsomes that were isolated simultaneously. Oxalate increased ATP-dependent Ca2+ uptake by the sarcolemmal but not the mitochondrial fraction, while azide inhibited mitochondrial but not sarcolemmal Ca2+ transport. The amount of Ca2+ bound in 10 min by these two fractions from a 0.3 μM free Ca2+ solution was similar, but the rate of Ca2+ uptake at 1 μM Ca2+ was greater for the mitochondrial than the sarcolemmal. fraction. The properties of Ca2+ binding by the microsomal fraction were intermediate between these two fractions. The results suggest that mitochondria have a greater potential for lowering intracellular Ca2+ activity in human myometrium than do sarcolemma or sarcoplasmic reticulum.

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