Ca2+ Modulation System of Myometrial Contraction During Gestation

This chapter aims to clarify some of the events that govern the contractile machinery by the intracellular Ca²⁺ modulation system in the myometrium. The shape of the action potential in both longitudinal and circular muscles of the myometrium also changes during gestation, and the configuration of the action potentials differs between the longitudinal and circular muscle membrane, except for the last stage and during paturition, according to the hormonal changes. Ca²⁺ is thought to play an essential role in regulating the contraction-relaxation cycle in the myometrium, as observed in other visceral smooth muscles. Many electrophysiological studies suggest that membrane properties may modify the Ca²⁺ influx from the extracellular source in uterine smooth muscle during gestation. The increase of Ca²⁺ concentration in smooth muscle cells favors the formation of a Ca²⁺-calmodulin complex. Myosin light chain kinase is activated by the Ca²⁺-calmodulin complex by phosphorylation to initiate a contraction.