CORRELATION BETWEEN ELECTRICAL ACTIVITY AND SPLITTING OF PHOSPHOLIPIDS BY SNAKE VENOM IN THE SINGLE ELECTROPLAX

— Cottonmouth moccasin snake venom (SV) was applied to the innervated membrane of the isolated single cell of the Sachs electric organ (electroplax) of the electric eel, Electrophorus electricus. Concentrations as low as 0.05 μg/ml irreversibly antagonized depolarization by carbamylcholine, whereas concentrations of 0.1 mg/ml or higher were required to directly and irreversibly depolarize and block electrical excitation. The active component of the venom was stable to boiling at acid pH, destroyed by boiling at alkaline pH and nondialyzable and corresponded to those fractions containing maximum phospholipase A activity demonstrable when isolated by paper electrophoresis and Sephadex filtration. Phospholipase C and lysolecithin in concentrations of 1 mg/ml and 0.2 mg/ml, respectively, depolarized and blocked electrical excitation, whereas lower concentrations did not antagonize depolarization by carbamylcholine. Triton X-100 (0.01 mg/ml) antagonized carbamylcholine, whereas 10-fold higher concentrations directly blocked electrical excitation. Hyaluronidase had no effect on resting or action potential but decreased the depolarizing response to carbamylcholine. At minimal concentrations which blocked the depolarizing response to carbamylcholine, SV caused only slight splitting of phospholipids in single cells of the Sachs organ. A concentration (1 mg/ml) of SV which blocked electrical excitation caused 80–100 per cent splitting of lecithin, phosphatidylethanolamine and phosphatidylserine, the three principal phospholipids of the electric tissue. Similar percentages of splitting of the latter two phospholipids but only about one-third of the lecithin occurred at SV concentration of 0.1 mg/ml. These results indicate that electrical excitability in the eel electroplax can be maintained in the presence of extensive phospholipid splitting. Depolarization and block of electrical excitation by relatively high concentrations of SV may have resulted from splitting of phospholipids, especially lecithin, or may have reflected action of lysophosphatide detergents produced as a result of the action of phospholipase A upon membranal phospholipids.