Sodium and calcium currents measured in isolated catfish horizontal cells under voltage clamp.

A low resistance suction microelectrode was used to record intracellularly from enzymatically dissociated horizontal cells obtained from catfish retina (Ictalurus punctatus). This microelectrode was connected to a voltage clamp circuit and the transmembrane currents were recorded during depolarizing and hyperpolarizing clamp pulses. Two fast transient inward currents were recorded, one sensitive to tetrodotoxin and one insensitive to this drug. A slower and persistent tetrodotoxin insensitive inward current was also recorded. The results indicate that separate membrane conductances exist for both sodium and calcium ions. We suggest that the action potential recorded from isolated horizontal cells is generated by both sodium and calcium currents.