Abstract
—Four homogeneous proteins having phospholipase A activity were separated and studied for their i.v. lethal effects in mice and nerve-muscle activity in the guinea pig diaphragm preparation. Fraction “j” had an ld 50 of 0.30 mg/kg, with 3.6 μg/ml of bath solution causing a decrease in the indirectly-elicited nerve-muscle contractions to 20% of control, without significantly changing the directly-elicited muscle contractions. Fraction “k 2” had an ld 50 of 0.021 mg/kg and caused a similar nerve or nerve-muscle block at 5 μg/ml of bath solution, without altering the directly-elicited contractions. Fraction “k 1” had an ld 50 of 0.58 mg/kg and produced less distinct but dose-related changes in the nerve or in nerve-muscle transmission, as well as weakening directly-elicited muscle contractions to within 60% of control. Fraction “l” had an ld 50 of 3.6 mg/kg but high doses of the fraction were required to produce changes in diaphragm contractility. High doses (60 and 195 μg/ml) produced marked effects on both the directly- and indirectly-elicited contractions, suggesting that this fraction affects the muscle directly.
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