Functional coupling between sodium - activated potassium channels and 1 voltage - dependent persistent sodium currents in cricket Kenyon cells

13 14 In this study, we examined the functional coupling between Na+-activated 15 potassium (KNa) channels and Na+-influx through voltage-dependent Na+ 16 channels in Kenyon cells isolated from the mushroom body of the cricket 17 Gryllus bimaculatus. Single channel activity of KNa channels was recorded 18 with the cell-attached patch configuration. The open probability (Po) of KNa 19 channels increased with increasing Na+ concentration in a bath solution, 20 whereas it decreased by the substitution of Na+ with an equimolar concen21 tration of Li+. The PO of KNa channels was also found to be reduced by bath 22 application of a high concentration of tetrodotoxin (TTX; 1 μM) and rilu23 zole (100μM), which inhibits both fast (INaf) and persistent Na+ (INaP) cur24 rents, whereas it was unaffected by a low concentration of TTX (10 nM), 25 which selectively blocks INaf. Bath application of Cd2+ at a low concentration 26 (50 μM), as an inhibitor of INaP, also decreased the Po of KNa channels. Con27 versely, bath application of the inorganic Ca2+ channel blockers Co2+ and Ni2+ 28 at high concentrations (500 μM) had little effect on the Po of KNa channels, 29 although Cd2+ (500 μM) reduced the Po of KNa channels. Perforated 30 whole-cell clamp analysis further indicated the presence of sustained out31 ward currents whose amplitude was dependent on the amount of Na+ influx. 32 Taken together, these results indicate that KNa channels could be activated 33 by Na+ influx passing through voltage-dependent persistent Na+ channels. 34 The functional significance of this coupling mechanism was discussed in re35 lation to the membrane excitability of Kenyon cells and its possible role in 36 the formation of long-term memory. 37