Neuromuscular effects of a toxic phospholipase A2 and its nontoxic homologue from the venom of the sea snake, Laticauda colubrina

Abstract

A single chain phospholipase A2 (LcPLA-II) and a homologous protein lacking enzymatic activity (LcPLH-I) isolated from the venom of the Solomon Island sea snake (Laticauda colubrina) were tested for effects on neuromuscular transmission and muscle contractility on chick biventer cervicis and mouse hemidiaphragm preparations. LcPLA-II (7.5 nM-1.5 microM) blocked indirectly elicited muscle contractions of both preparations. Low concentrations of LcPLA-II caused little change in sensitivity to acetylcholine, carbachol and KCl. The homologue LcPLH-I (375 nM-1.5 microM) reduced the responses of the biventer cervicis preparation to indirect stimulation and abolished responses to acetylcholine and carbachol, but it did not block KCl responses. These effects were due to minor contamination by a post-junctional neurotoxin. LcPLH-I (375 nM-750 nM) had no effect on indirectly stimulated hemidiaphragm preparations. It is concluded that LcPLA-II blocks neuromuscular transmission by a prejunctional action, and that the homologue lacking phospholipase A2 activity also lacks neuromuscular activity.