Figure 7. Block of the cation channel protects from CtVm-induced refractoriness in the intact bag cell neurone cluster.

In these experiments, the channel blocker (TTX or nifedipine) was first applied for 1 h, then CtVm was added along with the blocker for a second hour, the preparation was washed thoroughly over the course of a third hour, and finally the afferent connective was stimulated to test for the ability to produce an afterdischarge. A, block of the cation channel with TTX protects from CtVm-induced refractoriness to subsequent stimulation. Following wash of 100 μM TTX plus 100 μg ml⁻¹ CtVm, the cluster was capable of firing an afterdischarge upon electrical stimulation (stim, at bar, 2.5 ms pulses, 6 Hz, 20 V). B, block of voltage-dependent Ca²⁺ channels did not protect from CtVm-induced refractoriness to subsequent stimulation. Left, following wash of 100 μM nifedipine plus 100 μg ml⁻¹ CtVm, the cluster was refractory to electrical stimulation (stim, at bar). Right, recording from the same cluster at a higher sweep speed shows that while refractory, the cells were fully capable of firing compound action potentials upon stimulation (stim). The action potentials are obscured in the trace shown on the left because of the condensed time scale.