Abstract
Effects of phospholipase C(PLC) on factors involved in smooth muscle contraction were investigated in longitudinal muscle of the guinea pig antrum. This agent irreversibly reduced spontaneous contraction and action potentials; partially after 30 min and, sometimes, completely after 60 min of exposure to PLC. The membrane depolarized about 8 mV from the control level in 30 min and 16 mV in 60 min. ACh- and KCl-induced contracture were inhibited in an external Ca2+ concentration range from zero to three times normal. The phasic component of KCl-induced contracture was abolished occasionally in normal Ca2+ concentration, and frequently in Ca2+ -free solution. Ca-uptake by antrum tissue, which was the same for control, ACh-, and KCl-induced contracture before PLC treatment, was not statistically different in PLCtreated control, but the value decreased during ACh-induced, and increased during KCl-induced contracture after PLC treatment. The contents of phosphatidylcholine and phosphatidylethanolamine were reduced slightly after PLC treatment, but this reduction was statistically significant. Substantial damage and modification of physical characteristics appeared in electron micrographs of PLC-treated preparations. From the results it was concluded that changes in Ca2+ transport and membrane structural damage both contribute to inhibition of smooth muscle activity by PLC.
