NA-ACTIVATED NONSELECTIVE CATION CHANNELS IN PRIMARY OLFACTORY NEURONS()

1. Excised inside-out patch recordings were used to describe a novel c ation channel from cultured lobster olfactory receptor neurons that is activated by [Na+](i). 2. The channel is reversibly activated by intr acellular Na+ as low as 5 mM. The half-effect concentration of intrace llular Na+ is similar to 60 mM at -60 mV. The dependence of the channe l open probability on [Na+](i) is sigmoidal with a Hill coefficient of 3.1, indicating that more than one Na+ must bind to activate the chan nel. 3. The channel is equally permeable to Na+, K+, and Li+. In symme trical 210 mM Na+, the open channel current-voltage relationship shows slight inward rectification at positive potentials. The slope conduct ance of the channel is 107 pS between -90 and 0 mV. 4. Although the ch annel is not activated by voltage in the absence of intracellular Na+, the gating of the channel is dependent on voltage as well as [Na+](i) and [Na+](o). 5. Both intracellular Ca2+ and Mg2+ reversibly affect c hannel activity in a concentration-dependent manner starting at 1 mu M . Ca2+ decreases both the open probability and the single channel ampl itude, whereas Mg2+ decreases the open probability but has no effect o n the single channel amplitude. Ba2+ (5 mM), but not 20 mM Cs+ and 100 mu M amiloride, reversibly block the channel. 6. We speculate that th is novel cation channel regulates neuronal excitability by accentuatin g the rate and/or the magnitude of depolarization of the cell to odors .