Effects of alpha-bungarotoxin and d-tubocurarine on the post-tetanic potentiation of the mouse diaphragm twitch tension.

Effects of alpha-bungarotoxin (alpha-BuTX, 0.037-0.062 microM) and d-tubocurarine (d-Tc, 0.7-2.2 microM) on the post-tetanic potentiation (PTP) of the twitch tension were studied on the isolated mouse diaphragm preparation. In normal physiological solution, maximum PTP was obtained after 100 Hz tetanic stimulation for 5 sec. In preparations partially blocked by alpha-BuTX, PTP was less than in control preparations if tetanically stimulated at 100-200 Hz for 5-10 sec. In contrast, in preparations partially blocked by d-Tc (1-2.2 microM), PTP was increased if a higher frequency (500 Hz) was applied. This increase of the effect was independent of the duration of tetanic stimulation. Thus, d-Tc and alpha-BuTX have a different effect on PTP. The irreversibility of alpha-BuTX may contribute to the differences in mode of action of alpha-BuTX and d-Tc on the PTP of the twitch tension of the isolated mouse diaphragm.