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Na⁺-activated K⁺ channels in small dorsal root ganglion neurones of rat

Ulrike Bischoff, Werner Vogel and Boris V. Safronov

1. Whole-cell Na⁺-activated K⁺ (K_Na) channel currents and single K_Na channels were studied with the patch-clamp method in small (20-25 µm) dorsal root ganglion (DRG) neurones in slices of rat dorsal root ganglia.

2. The whole-cell K_Na channel current was identified as an additional K⁺-selective leakage current which appeared after cell perfusion with internal solutions containing different [Na⁺]. The concentration for half-maximal activation of K_Na channel current was 39 mM and the Hill coefficient was 3·5. At [Na⁺]_i above 12 mM, K_Na channel current dominated the unspecific leakage current. The ratio of maximum K_Na channel current to unspecific leakage current was 45.

3. K_Na channel current was not activated by internal Li⁺. It was suppressed by external 20 mM Cs⁺ but not by 10 mM tetraethylammonium.

4. Single K_Na channels with a conductance of 142 pS in 155 mM external K⁺ (K⁺_o)-85 mM internal K⁺ (K⁺_i) solutions were observed at a high density of about 2 channels µm^-2.

5. In two-electrode experiments, a direct correlation was seen between development of whole-cell K_Na channel current and activation of single K_Na channels during perfusion of the neurone with Na⁺-containing internal solution.

6. Under current-clamp conditions, K_Na channels did not contribute to the action potential. However, internal perfusion of the neurone with Na⁺ shifted the resting potential towards the equilibrium potential for K⁺ (E_K). Varying external [K⁺] indicated that in neurones perfused with Na⁺-containing internal solution the resting potential followed the E_K values predicted by the Nernst equation over a broader voltage range than in neurones perfused with Na⁺-free solution.

7. It is concluded that the function of K_Na channels has no links to firing behaviour but that the channels could be involved in setting or stabilizing the resting potential in small DRG neurones.

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