Figure 5.

αM-MIIIJ (10 μM) blocks MEPSPs in goldfish intercostal (IC) muscles. Intracellular recordings, performed as described in Methods, were obtained successively from six muscle fibers, A through F. Each data point represents the mean peak amplitude ± SD of at least 30 events. Recordings were made before (fibers A–C) and during (fibers C’–F) exposure to αM-MIIIJ (1 μM). After recordings from fiber C were acquired, the bath was supplemented with a high concentration of αM-MIIIJ such that its final concentration in the bath was 1 μM, and the recording recommenced (fiber C’) until the resting potential was abruptly lost. The resting potentials (in mV) of the respective fibers fibers were as follows: −67 (fiber A), −62 (fiber B), −92 (fiber C), −84 (fiber C’), −98 (fiber D), −65 (fiber E), and −101 (fiber F). In fibers D–F, no discernable MEPSPs were observed above the noise and indicated the block by 1 μM αM-MIIIJ was > 80% in each case.