An electrophysiological study of the action of methylmercuric chloride and mercuric chloride on the sciatic nerve-sartorius muscle preparation of the frog

Abstract

Effects of methylmercuric chloride (CH 3HgCl) and mercuric chloride (HgCl 2) on electrical properties of muscle fibers and on neuromuscular transmission were studied in the isolated sciatic nerve-sartorius muscle preparation of the frog with an intracellular recording technique. HgCl 2 at 0.04 m m produced decreases in resting potential, effective resistance, and the amplitude of action potentials, and eventually led to electrical inexcitability. On the other hand, 0.04 m m CH 3HgCl produced little effect on these electrical properties but at a concentration of 0.4 m m caused depolarization and inexcitability. Both compounds caused a large increase in the frequency of spontaneous transmitter release. The increase by CH 3HgCl was associated with increase in the amplitude of mEPPs, whereas that by HgCl 2 was associated with a decrease, the latter being due to decreases in resting potential and effective resistance. Both compounds also caused a transient increase in evoked transmitter release. Eventually, either spontaneous or evoked transmitter release was similarly suppressed after long-term exposure. It may be concluded that the primary action of CH 3HgCl is on the presynaptic site, whereas that of HgCl 2 is both on the pre-and postsynaptic sites.