An analysis of Na⁺ currents in rat olfactory receptor neurons

Abstract

Na⁺ currents were observed in acutely-dissociated adult rat olfactory receptor neurons using the whole-cell recording techniques. The threshold for current activation was near −70mV and currents were fully activated by −10 mV (midpoint: −45 mV). Steady-state inactivation was complete at potentials more positive than −70mV and half complete at −110mV (±<1, n=8). Complete recovery from inactivation required one second at −100 mV (n=7). The addition of 10 μM tetrodotoxin or 1 mM Zn²⁺ to the external solution was required to completely block the current. The current differs from those in amphibian and cultured neonatal rat olfactory neurons in its unusually negative voltage-dependence and slow recovery. Since mammalian olfactory neurons have very high input resistances, physiological resting potentials cannot usually be measured using whole-cell recording techniques. However, predominantly-capacitatively-coupled spikes activated by depolarisation were frequently observed in cell-attached patches. This indicates that the cells were excitable and implies that they must have had resting potentials more negative than −90 mV in order for this current to underlie the action potential.