IDENTIFICATION AND CHARACTERIZATION OF A CA2-SENSITIVE NONSPECIFIC CATION CHANNEL UNDERLYING PROLONGED REPETITIVE FIRING IN APLYSIA NEURONS()

The afterdischarge of Aplysia bag cell neurons has served as a model s ystem for the study of phosphorylation-mediated changes in neuronal ex citability. The nature of the depolarization generating the afterdisch arge, however, has remained unclear. We now have found that venom from Conus textile triggers a similar prolonged discharge, and we have ide ntified a slow inward current and corresponding channel, the activatio n of which seems to contribute to the onset of the discharge. The slow inward current is voltage-dependent and Ca2+-sensitive, reverses at p otentials slightly positive to 0 mV, exhibits a selectivity of K congr uent to Na >> Tris > N-methyl-D-glucamine (NMDG), and is blocked by hi gh concentrations of tetrodotoxin. Comparison of these features with t hose observed in channel recordings provides evidence that a Ca2+-sens itive, nonspecific cation channel is responsible for a slow inward cur rent that regulates spontaneous repetitive firing and suggests that mo dulation of the cation channel underlies prolonged changes in neuronal response properties.