NONSELECTIVE SUPPRESSION OF VOLTAGE-GATED CURRENTS BY ODORANTS IN THENEWT OLFACTORY RECEPTOR-CELLS

Effects of odorants on voltage-gated ionic channels were investigated in isolated newt olfactory receptor cells by using the whole cell vers ion of the patch-clamp technique. Under voltage clamp, membrane depola rization to voltages between -90 mV and +40 mV from a holding potentia l (Vh) Of -100 mV generated time- and voltage-dependent current respon ses; a rapidly (< 15 ms) decaying initial inward current and a late ou tward current. When odorants (1 mM amyl acetate, 1 mM acetophenone, an d 1 mM limonene) were applied to the recorded cell, the voltage-gated currents were significantly reduced. The dose-suppression relations of amyl acetate for individual current components (Na+ current: I-Na, T- type Ca2+ current: I-Ca,I-T, L-type Ca2+ current: I-Ca,I-L, delayed re ctifier K+ current: I-Kv and Ca2+-activated K+ current: I-K(Ca)) could be fitted by the Hill equation. Half-blocking concentrations for each current were 0.11 mM (I-Na), 0.15 mM (I-Ca,I-T), 0.14 mM (I-CaL), 1.7 mM (I-Kv), and 0.17 mM (I-K(Ca)), and Hill coefficient was 1.4 (I-Na) , 1.0 (I-Ca,I-T), 1.1 (I-Ca,I-L), 1.0 (I-Kv), and 1.1 (I-K(Ca)), sugge sting that the inward current is affected more strongly than the outwa rd current. The activation curve of I-Na was not changed significantly by amyl acetate, while the inactivation curve was shifted to negative voltages; half-activation voltages were -53 mV at control, -66 mV at 0.01 mM, and -84 mV at 0.1 mM. These phenomena are similar to the supp ressive effects of local anesthetics (lidocaine and benzocaine) on I,, in various preparations, suggesting that both types of suppression ar e caused by the same mechanism. The nonselective blockage of ionic cha nnels observed here is consistent with the previous notion that the su ppression of the transduction current by odorants is due to the direst blockage of transduction channels.