A TOXIN FROM THE VENOM OF THE PREDATOR SNAIL CONUS-TEXTILE MODULATES IONIC CURRENTS IN APLYSIA BURSTING PACEMAKER NEURON

Conus textile crude venom and a peptide component ('King Kong' toxin) purified from this venom, alter membrane excitability of Aplysia neuro ns. Venom, applied to the medium bathing an abdominal ganglion, change s dramatically the electrical activity of bursting pacemaker neuron. T he effects on bursting neuron R15 was examined in current-clamp and vo ltage-clamp modes. A dual phase effect of both the venom and the purif ied toxin were observed. The first phase starts immediately after veno m or toxin application and is observed as an increase in membrane exci tability, resulting in an enhancement of bursting. The second phase be gins about 15 min later and consists of a long-lasting hyperpolarizati on. The dual phase effect of the venom and the toxin persists even whe n synaptic input is eliminated either by axotomy, or by recording from freshly dissociated neurons or from neurons in primary cell culture. The ionic currents affected are an inward current, I(NSR), which is ac tivated upon depolarization and an anomalously rectifying potassium cu rrent, I(R), which is activated upon hyperpolarization. In the first p hase of toxin action I(NSR) is increased. In the second phase both the venom and the toxin block I(NSR) and increase I(R). The toxin effects may be due to complex alteration of one or more second messenger casc ades rather than a direct action on ion channels.