Diamide acts intracellularly to enhance transmitter release: The differential permeation of diamide, DIP, DIP + 1 and DIP + 2 across the nerve terminal membrane

Abstract

The actions of the new potent thiol oxidizing agents, diazene dicarboxylic acid bis (N′-methyl piperazide) (DIP) and the N′-methyl iodide (DIP + 1) and the bis-N′-methyl iodide (DIP + 2) salts of DIP, were tested at the frog neuromuscular junction. At 20°C, DIP was as fast as the thiol oxidizing agent, diamide, in evoking transmitter release but was appreciably less effective at 6°C. DIP + 1 and DIP + 2 did not increase transmitter release. Since the three agents are potent oxidizers of glutathione and since the effectiveness of the compounds appears to depend on their a ability to exist, at least in part, in a neutral form at physiological pH, it is concluded that their action as promoters of transmitter release depends on their ability to permeate nerve terminal membranes. Thus, both diamide and DIP act to increase transmitter release by the intracellular oxidation of glutathione. The two charged agents, DIP + 1 and DIP + 2, are potent muscular depolarizing agents. It is probable that the quaternary nitrogen groups of these compounds render them cholinomimetics.