Na(+)-activated nonselective cation channels in primary olfactory neurons.
1. Excised inside-out patch recordings were used to describe a novel cation channel from cultured lobster olfactory receptor neurons that is activated by [Na+]i. 2. The channel is reversibly activated by intracellular Na+ as low as 5 mM. The half-effect concentration of intracellular Na+ is approximately 60 mM at -60 mV. The dependence of the channel 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 channel. 3. The channel is equally permeable to Na+, K+, and Li+. In symmetrical 210 mM Na+, the open channel current-voltage relationship shows slight inward rectification at positive potentials. The slope conductance of the channel is 107 pS between -90 and 0 mV. 4. Although the channel 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 channel activity in a concentration-dependent manner starting at 1 microM. Ca2+ decreases both the open probability and the single channel amplitude, whereas Mg2+ decreases the open probability but has no effect on the single channel amplitude. Ba2+ (5 mM), but not 20 mM Cs+ and 100 microM amiloride, reversibly block the channel. 6. We speculate that this novel cation channel regulates neuronal excitability by accentuating the rate and/or the magnitude of depolarization of the cell to odors.
Zhainazarov
A B
AB
Whitney Laboratory, University of Florida, St. Augustine 32086, USA.
Ache
B W
BW
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007473:Ion Channels / Q000187:drug effects* / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008121:Nephropidae / Q000502:physiology*; D018034:Olfactory Receptor Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D012964:Sodium / Q000494:pharmacology*
D007473:Ion Channels; D012964:Sodium; D008274:Magnesium; D002118:Calcium