Potassium current activated by intracellular sodium in quail trigeminal ganglion neurons.
Whole-cell voltage clamp and single-channel recordings were performed on cultured trigeminal ganglion neurons from quail embryos in order to study a sodium-activated potassium current (KNa). When KNa was activated by a step depolarization in voltage clamp, there was a proportionality between KNa and INa at all voltages between the threshold of INa and ENa. Single-channel recordings indicated that KNa could be activated already by 12 mM intracellular sodium and was almost fully activated at 50 mM sodium. 100 mM lithium, 100 mM choline, or 5 microM calcium did not activate KNa. The relationship between the probability for the channel to be open (Po) vs. the sodium concentration and the relationship of KNa open time-distributions vs. the sodium concentration suggest that two to three sodium ions bind cooperatively before KNa channels open. KNa channels were sensitive to depolarization; at 12 mM sodium, a 42-mV depolarization caused an e-fold increase in Po. Under physiological conditions, the conductance of the KNa channel was 50 pS. This conductance increased to 174 pS when the intra- and extracellular potassium concentrations were 75 and 150 mM, respectively.
Haimann
C
C
Department of Physiology, Hôpital Cantonal Universitaire, Geneva, Switzerland.
Bernheim
L
L
Bertrand
D
D
Bader
C R
CR
D000818:Animals; D002478:Cells, Cultured; D008564:Membrane Potentials; D010539:Permeability; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D011784:Quail; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism; D012668:Trigeminal Ganglion / Q000378:metabolism*
D015221:Potassium Channels; D015222:Sodium Channels; D012964:Sodium; D011188:Potassium