Effects of a myotoxic Asp49 phospholipase A 2 (ACL-I PLA 2) isolated from Agkistrodon contortrix laticinctus snake venom on water transport in the isolated toad urinary bladder

Abstract

An Asp49 PLA 2 (ACL-I PLA 2) was purified from the venom of Agkistrodon contortrix laticinctus by gel filtration and cation-exchange chromatography. It has a relative molecular mass of 14,000, and its N-terminal sequence has more than 65% of identity with other snake venom PLA 2s. ACL-I PLA 2 injected into the Tibialis anterior muscle of rats and mice at doses of 0.3 and 1.6 mg/kg, respectively, induced muscle fiber necrosis, cellular infiltration and edema 3 and 48 h after injection. The effect of the purified enzyme on water permeability was tested in the isolated toad urinary bladder. Water flow through the membrane was measured gravimetrically in bag preparations of the bladder. ACL-I PLA 2 (20 nM) did not significantly alter the water permeability in the bladder preparations, whereas ACL myotoxin (ACLMT), a Lys49 PLA 2 isolated from the same venom, at similar concentration significantly increased (81%) the water permeability. However, both toxins inhibited the AVP-stimulated water permeability. These results strongly suggest that PLA 2 activity is not involved in the ACLMT effect on water transport and the effect of ACL-I PLA 2 myotoxin on membrane permeability is mediated by mechanisms that are different in comparison to ACLMT.