Regenerative sodium and calcium currents in goldfish retinal ganglion cell somata

Whole-cell patch-clamp recordings were made from isolated goldfish retinal ganglion cell somata. Sodium- and calcium-dependent action potentials--blocked with tetrodotoxin (TTX) and Co2+ ions, respectively--were evoked under current-clamp. Depolarization of these somata under voltage clamp activated distinguishable Na+ and Ca2+ conductances: the former was permeable to Na+, blocked by TTX, impermeable to N-methyl-D-glucamine and tris(hydroxymethyl)aminomethane, and began to activate around -45 mV; the latter were permeable to Ca2+, but not Co2+, and began to activate around -55 mV. These results are consistent with recordings from carp, frog, salamander and rat retinal ganglion cells.