[Study of the active calcium transport mechanisms in uterine smooth muscle]

Calcium ions were shown to be actively accumulated in mitochondrial and microsomal fractions of uterine smooth muscle of rabbit and cattle. In presence of magnesium ions Ca2+ (10-6-10-4 M) activate microsomal ATPase from cattle uterus. The rate of formation and dissociation of the intermediate phosphorylated substance of Mg2+, Ca2+-ATPase was found to be lower in microsomes of smooth muscles than in sarcoplasmic reticulum of sceletal muscles. Serotonine (concentration 10-6 M) increased the dissociation of the intermediate phosphorylated substance from microsomes of uterine smooth muscle and decreased their capacity to bind Ca2+. At the same concentration serotonine inhibited the ATP-dependent accumulation of 45Ca by microsomes of uterine smooth muscle.