Effects of phospholipase A 2 from cobra and bee venom on the presynaptic membrane

Abstract

L. G. Magazanik, I. M. Gotgilf, T. I. Slavnova, A. I. Miroshnikov and U. R. Apsalon. Effects of phospholipase A 2 from cobra and bee venom on the presynaptic membrane. Toxicon 17, 477–488, 1979.—Phospholipases A 2 from bee venom and cobra venom have been isolated and studied. A parallelism was found between enzymatic activity and the ability to block spontaneous miniature end-plate potentials (m.e.p.p.'s) or end-plate potentials (e.p.p.'s) induced by nerve stimulation in the frog sartorius muscle. Different experimental procedures affected both enzymatic activity and blocking ability in qualitatively the same way. Thus, modification of the histidine residue in cobra venom phospholipase by bromophenacyl bromide or the removal of Ca-ions from the medium abolished both activities. Replacement of Ca 2+ by Sr 2+ inhibited both the enzymatic and presynaptic effects of cobra venom phospholipase, but did not inhibit the presynaptic action of bee venom phospholipase and decreased its enzymatic activity only 6-fold. Irreversible binding of cobra and bee venom phospholipase to the presynaptic membrane was found in Ca-free solution but Ca-ions were essential for the presynaptic blocking effect induced by these phospholipases. A reduction in the effect of high K + on m.e.p.p. frequency was observed after cobra venom phospholipase treatment. The similar effects of hypertonic sucrose solution and the mitochondrial poison TTFB (4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole) were changed only slightly by bee and cobra venom phospholipase pretreatment. It is concluded that the mechanism of presynaptic blockade induced by bee venom and cobra venom phospholipase consists mainly of damage to sites of release at the presynaptic membrane. There are also some signs of disturbances of depolarization-secretion coupling and of the process of formation of new quanta. The possible functional role of enzymatic activity in the presynaptic effect is discussed.