Calcium requirement of uterine contraction induced by PGE 1: Importance of intracellular calcium stores

Abstract

The contraction of the rat uterus in response to PGE 1 in high K + medium and in Ca-free solution which contained EDTA has been investigated in order to examine whether excitation-contraction coupling involves the release of Ca from an intracellular store. In uterus maximally contracted by K +, cumulative concentrations of PGE 1 (1.25 – 20 ng/ml) caused maintained concentration-dependent contraction. PGE 1 induced sustained contraction of rat uterus in Ca-free medium after incubation with 3mM EDTA for 50 min. In these conditions the involvement of extracellular Ca is highly unlikely. The PGE 1-induced contraction could be repeated without exposure to external Ca ions and with only slight reduction in magnitude. The PGE 1 concentrations required to elicit uterine contraction in Ca-free solution were about 1000 times higher than the effective doses in KCl-depolarized uterus. In conclusion, the present investigation shows that Ca influx is not essential for PGE 1-induced contraction of rat uterus, although extracellular Ca enhances it presumably by increasing the free Ca levels in the cytosol.