A transient outward cationic current activated by Na+ influx into frog visual neurones in vitro

Whole cell patch clamp recording from neurones of a slice preparation of the frog optic tectum showed that depolarizing step commands from -70 mV holding potential generated a fast inward current always followed by a fast outward current. The fast outward current was blocked by tetrodotoxin (TTX) or 4-aminopyridine (4-AP), or by replacing external Na+ with Li+. When the patch pipette contained Cs+ instead of K+ the outward current was fully preserved, suggesting that the membrane channels responsible for this response were relatively non-selective in their permeability properties. This current (termed Icat) is a novel example of a non-specific cationic current dependent on influx of Na+ and presumably important to control the firing characteristics of these cells.