Figure 9.

αM-MIIIJ (10 μM) protects zebrafish nAChRs against slowly-reversible block by α-EI and α-bungarotoxin (α-BgTX). ACh-gated currents from oocytes expressing zebrafish nAChRs were obtained as described in Methods. A given oocyte was first exposed to 10 μM αM-MIIIJ for 10 min. in a static bath, then perfused to observe the time course of recovery from block (open circles). The oocyte was then exposed again to 10 μM αM-MIIIJ for 5 min. in a static bath, after which the bath was supplemented with either 1 μM α-EI (open squares in panels A, B, and C) or 10 μg/mL α-BgTX (open squares in panels D, E, and F) and allowed to sit for another 5 min before the bath perfusion was recommenced. Finally, in a separate experiment, a given oocyte was exposed to either 1 μM α-EI alone (panels A, B, and C) or 10 μg/mL of α-BgTX alone (panels D, E, and F) for 5-min in a static bath before bath perfusion was recommenced (solid triangles). The time courses of recovery from block during the perfusion following the static-bath exposure to toxin(s) are plotted. Recovery from block following exposure to α-EI alone or α-BgTX alone was very slow in all panels (solid triangles). Furthermore, in all instances, except panel D, pre- and concurrent exposure to αM-MIIIJ prevented persistent block by α-EI and α-BgTX (as evident from similarity of time courses curves denoted by open circles and open squares). The divergent open-circle and open-square curves in panel D indicate that αM-MIIIJ only partially protected the αβδγ receptor against block by α-BgTX. α-BgTX use in these experiments was derivatized with tetramethylrhodamine (same stock solution as that used in fluorescence imaging experiments described below).