Triton detergents and the frog neuromuscular end-plate: An electrophysiological and ultrastructural study

Abstract

The effects of the nonionic detergents Triton X-45 and Triton X-100 were studied in the frog muscle end-plate by intracellular recordings of spontaneous miniature end-plate potentials (mepps) and the potential changes produced by iontophoretic application of acetylcholine (ACh-potentials). The ultrastructural changes produced by Triton X-100 were studied by transmission electron microscopic and freeze-fracture techniques. Triton X-45 and Triton X-100 caused a rapidly developing reduction of the amplitude of the mepp. The response to iontophoretic application of acetylcholine was reduced by Triton X-100. Following return to normal Ringer solution the ACh-potentials recovered, although not completely. The dissociation constant calculated from the rate constants for onset and offset of the reaction (Kd = k2/k1) was 5-50 .mu.M depending on the type of stoichiometric reaction presumed to occur between Triton X-100 and the cholinergic receptors. The ultrastructural changes observed indicate that the nerve terminal plasma membrane and mitochondria are affected by Triton X-100. Leakage of Ca2+ from the latter may therefore be the cause of the increase in mepp frequency. The influence on the amplitude of the mepp and the ACh-potentials can be attributed to a direct effect of the detergent on the acetylcholine receptor protein.