[Effect of divalent metal ions--stimulants of uterine contractile activity--on the Mg2+, ATP-dependent transport of Ca2+ in the myometrial sarcolemma fraction].

Mn2+, Co2+, Zn2+ and Cu2+ were shown to inhibit the Mg2+-ATP-dependent accumulation of 45Ca2+ in the fraction of cytoplasmic membranes. Mechanism of inhibitory effect of the Me2+ is considered. It is assumed that the cations, exhibiting higher affinity to ATP as compared with Mg2+, contributed to dissociation of the actual substrate of the enzymatic reaction Mg2+-ATP as well as to formation of the chelate complexes of the Me2+-ATP type; these complexes participated in the transport of Ca2+ less effectively as compared with the true substrate Mg2+-ATP. Among the essential factors responsible for an increase in the contractile activity of uterus in response to divalent ions of metals, accumulated into cells, elevation of Ca2+ concentration appears to occur in myocytes due to inhibition of the Mg2+-ATP-dependent output of Ca2+ from myoplasm into interstitial space.