PROPERTIES OF WHOLE-CELL CURRENTS IN ISOLATED OLFACTORY NEURONS FROM THE CHILEAN TOAD CAUDIVERBERA-CAUDIVERBERA

Isolated olfactory neurons from the chilean toad Caudiverbera caudiverbera were found to possess a same set of currents. Outward currents, made of a delayed rectifier and a Ca2+-dependent component, were blocked by replacing K+ by Cs+ in the patch pipette, in the presence of millimolar concentrations of tetraethylammonium and 4-aminopyridine in the external solution. Inward currents were made of a transient and a maintained component. The transient was abolished in the absence of external Na+ and was blocked by tetrodotoxin, with an apparent dissociation constant (K(D app)) of 25.4 +/- 0.3 nM. The maintained inward currents were suppressed on removing external Ca2+, could be carried also by Ba2+, and were selectively blocked by Cd2+ (K(D app) = 3.2 +/- 1.3 muM). A variety of agents found to block the maintained Ca2+ inward currents, including Co2+ and Ni2+ at millimolar concentrations, and nifedipine, verapamil, amiloride, and the amiloride analogue benzamil, at micromolar concentrations, were also effective in either modifying the gating of, or in blocking, the transient inward currents.