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Journal of Neuroscience, Vol 8, 4379-4393, Copyright © 1988 by Society for Neuroscience
Ionic currents of Drosophila neurons in embryonic cultures
L Byerly and HT Leung
Department of Biological Sciences, University of Southern California, Los Angeles 90089.
Drosophila offers a unique opportunity to determine how the genome codes
for ionic channels in an organized nervous system. Considerable progress
has already been made in studying the molecular biology of Drosophila K
channels. In order for similar progress to be made on neuronal
voltage-dependent Ca channels, a physiological preparation is needed in
which the function of these channels can be directly studied. The
patch-clamp studies reported here show that cultures of embryonic
Drosophila cells (Seecof and Unanue, 1968) meet this need. These cultures
provide the first opportunity to study with voltage-clamp techniques the Ca
and Na currents of Drosophila neurons. The focus of these studies is on the
Ca current; however, descriptions of the K and Na currents are also given
since they help to characterize the cells studied and the quality of the
voltage clamp. The voltage-dependent K, Na, and Ca currents of Drosophila
neurons are very similar to those of molluscan neurons and other better
studied neurons. The K currents are the largest currents in these neurons,
averaging over 300 pA at +20 mV. There are 2 classes of Ca-independent K
currents, inactivating currents that are 4-AP sensitive, and
noninactivating currents that are insensitive to 4-AP. A large fraction of
the K currents are located in the somal membrane. The Na currents are TTX
sensitive and probably located in the processes. The peak amplitudes of the
Ca currents vary from 0 to over 100 pA in these neurons, averaging 40 pA.
With 5 mM external Ca2+ or Ba2+, the Ba currents are about twice as large
as the Ca currents. Although 100 microM Cd2+ completely blocks the Ca
current, organic blockers have very little effect. Variable inactivation
characteristics and sensitivity to washout suggest the possibility of
multiple types of Ca channels. A search for single-channel Ba currents in
the somal membrane was unsuccessful.
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