干旱区生态环境知识资源中心

Voltage-dependent outward currents were studied in freshly dissociated somata of locust lamina cells. These currents were recorded in 142 somata using the whole-cell patch-clamp technique, By measuring the reversal potential at altered external [K+] and by replacing internal K+ with Cs+, we determined that the outward currents were carried by K+. The outward currents consist of a transient A-type K+ current (K-A) and a delayed-rectifier-like K+ current (K-D), Amongst the cells studied, we observed two distinct groups of cells. The most obvious difference between the two groups is that in group I cells the total outward current is dominated by K-A (K-A/K-D=12.5), whereas in group II cells K-A makes a smaller contribution (K-A/K-D=2.1). Furthermore, in cells of group I, the K-A current shows a steeper voltage-dependence of activation, where V-G50 is -29.9 mV and s is 11.9 (N=22), and inactivation, where V-I50 is -84.5 mV and s is -6.3 (N=18), compared with the K-A current in cells of group II: V-G50=-7.9 mV; s=26.6 (N=36) and V-I50=-68.4 mV; s=-7.5 (N=21) (V-G50 is the voltage at which the whole-cell conductance G is half-maximally activated, V-I50 is the voltage of half-maximal inactivation and s is the slope of the voltage-dependence), The transient K-A current in group I cells decayed mono-exponentially. The decay of the K-A current in group II cells was fitted with a double-exponential curve and was significantly faster than in group I cells. In contrast to the large differences in K-A currents, the K-D currents appeared to be quite similar in the two groups of cells.