Penicillin decreases chloride conductance in crustacean muscle: a model for the epileptic neuron

The effects of penicillin were studied on the neuromuscular preparation of the ghost crab, Ocypoda cursor. Penicillin in doses lower than 2mM reduced both the amplitude of inhibitory junction potentials and conductance increases induced by external application of GABA. The nature of the latter effect appears to be 2-fold, a weaker competitive inhibition and a more powerful non-competitive effect which may be ionophore blockade. Penicillin in concentrations above 2 mM diminished resting conductance, especially that of chloride. The action of penicillin is, in general, to decrease chloride conductance in this preparation. The crustacean neuromuscular preparation may provide a useful analogue for understanding penicillin evoked epilepsy. The reduced chloride conductance could explain decreased inhibition, increased excitation and depolarization shifts in cortical neurons.