Identification and characterization of a Ca2+-sensitive nonspecific cation channel underlying prolonged repetitive firing in Aplysia neurons

Abstract

The afterdischarge of Aplysia bag cell neurons has served as a model system for the study of phosphorylation-mediated changes in neuronal excitability. The nature of the depolarization generating the afterdischarge, however, has remained unclear. We now have found that venom from Conus textile triggers a similar prolonged discharge, and we have identified a slow inward current and corresponding channel, the activation of which seems to contribute to the onset of the discharge. The slow inward current is voltage-dependent and Ca2+ -sensitive, reverses at potentials slightly positive to 0 mV, exhibits a selectivity of K ≅ Na ≫ Tris > N-methyl-D-glucamine (NMDG), and is blocked by high concentrations of tetrodotoxin. Comparison of these features with those observed in channel recordings provides evidence that a Ca2+ -sensitive, nonspecific cation channel is responsible for a slow inward current that regulates spontaneous repetitive firing and suggests that modulation of the cation channel underlies prolonged changes in neuronal response properties.