Affiliation:
1. Universitat Hamburg, Zoologisches Institut, Neurophysiologie, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany. C_Benkenstein@public.uni-hamburg.de.
Abstract
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 (KA) and a delayed-rectifier-like K+ current (KD). 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 KA (KA/KD=12.5), whereas in group II cells KA makes a smaller contribution (KA/KD=2.1). Furthermore, in cells of group I, the KA current shows a steeper voltage-dependence of activation, where VG50 is −29.9 mV and s is 11.9 (N=22), and inactivation, where VI50 is −84.5 mV and s is −6.3 (N=18), compared with the KA current in cells of group II: VG50=−7.9 mV; s=26.6 (N=36) and VI50=−68.4 mV; s=−7.5 (N=21) (VG50 is the voltage at which the whole-cell conductance G is half-maximally activated, VI50 is the voltage of half-maximal inactivation and s is the slope of the voltage-dependence). The transient KA current in group I cells decayed mono-exponentially. The decay of the KA 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 KA currents, the KD currents appeared to be quite similar in the two groups of cells.
Publisher
The Company of Biologists
Subject
Insect Science,Molecular Biology,Animal Science and Zoology,Aquatic Science,Physiology,Ecology, Evolution, Behavior and Systematics
Cited by
7 articles.
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