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

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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 (m.e.p.p.'s) and the potential changes produced by iontophoretic application of acetylcholine (ACh‐potentials). In addition, the ultra‐structural changes produced by Triton X‐100 were studied by transmission electron microscopic and freeze‐fracture techniques. It was found that Triton X‐45 and Triton X‐100 caused a rapidly developing reduction of the amplitude of the m.e.p.p.'s. The response lo 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/kl) was 5–50 μM depending on the type of stoichiometric reaction presumed to occur between Triton X‐100 and the cholinergic receptor. 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 m.e.p.p. frequency. It is concluded that the influence on the amplitude of the m.e.p.p.'s and the ACh‐potentials can be attributed to a direct effect of the detergent upon the acetylcholine receptor protein.