Very negative potential for half-inactivation of, and effects of anions on, voltage-dependent sodium currents in acutely isolated rat olfactory receptor neurons

Previous measurements with CsF pipette solutions using whole-cell patch-cla mp techniques in dissociated rat olfactory receptor neurons (ORNs) indicate d that the Sodium currents had very negative inactivation characteristics w ith the implication that the cell resting potential must also normally have a very negative value. This study supports the conclusions that such an ef fect was real and not dependent on either the nature of the pipette anions or the recording situation previously used. For all pipette solutions, sodi um currents showed a threshold activation approximate to -80 mV and half-ma ximal activation voltages approximate to -55 with half-inactivation potenti al less than or equal to -100 mV, without being significantly affected by t he replacement of F- by other pipette anions (H2PO4- and acetate(-)) or the addition of nucleotides and glutathione (which did cause a very slight pos itive shift). F-, followed by H2PO4- and to a much lesser extent by acetate (-), was the most favorable pipette anion for obtaining good seals and whol e-cell sodium currents in these extremely small ORNs. These results implied that resting potentials, for viable responsive cells, should be more negat ive than about -90 mV, as supported by the observation that action potentia ls could only be evoked from holding potentials more negative than -90 mV.