Journal of Neuroscience, Vol 8, 2556-2570, Copyright © 1988 by Society for Neuroscience
Voltage-gated potassium channels in larval CNS neurons of Drosophila
CK Solc and RW Aldrich
Department of Neurobiology, Stanford University School of Medicine, California 94305.
The availability of genetic, molecular, and biophysical techniques makes
Drosophila an ideal system for the study of ion channel function. We have
used the patch-clamp technique to characterize voltage-gated K+ channels in
cultured larval Drosophila CNS neurons. Whole-cell currents from different
cells vary in current kinetics and magnitude. Most of the cells contain a
transient A-type 4-AP-sensitive current. In addition, many cells also have
a more slowly inactivating TEA-sensitive component and/or a sustained
component. No clear correlation between cell morphology and whole-cell
current kinetics was observed. Single- channel analysis in cell-free
patches revealed that 3 types of channels, named A2, KD, and K1 can account
for the whole-cell currents. None of these channels requires elevated
intracellular calcium concentration for activation. The A2 channels have a
conductance of 6-8 pS and underlie the whole-cell A current. They turn on
rapidly, inactivate in response to depolarizing voltage steps, and are
completely inactivated by prepulses to -50 mV. The KD (delayed) channels
have a conductance of 10-16 pS and can account, in part, for the more
slowly inactivating component of whole-cell current. They have longer open
times and activate and inactivate more slowly than the A2 channels. The K1
channels have a slope conductance, measured between 0 and +40 mV, of 20-40
pS. These channels do not inactivate during 500 msec voltage steps and thus
can contribute to the sustained component of current. They exhibit complex
gating behavior with increased probability of being open at higher
voltages. Although the K1 channels are sufficient to account for the
noninactivating component of whole- cell current, we have observed several
other channel types that have a similar voltage dependence and average
kinetics.