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The Journal of Neuroscience, August 1, 2000, 20(15):5748-5755
Metabolic Stress Reversibly Activates the Drosophila
Light-Sensitive Channels TRP and TRPL In Vivo
Keren
Agam1,
Mark
von Campenhausen2,
Simon
Levy3,
Hagit Cohen
Ben-Ami1,
Boaz
Cook1,
Kuno
Kirschfeld2, and
Baruch
Minke1
1 Department of Physiology and the Kühne Minerva
Center for Studies of Visual Transduction, The Hebrew
University-Hadassah Medical School, Jerusalem 91120, Israel,
2 Max Planck-Institut für biologische Kybernetik,
72076, Tübingen, Germany, and 3 Department of
Physiology, Boston University School of Medicine, Boston, Massachusetts
02118
Drosophila transient receptor potential (TRP) is a
prototypical member of a novel family of channel proteins underlying
phosphoinositide-mediated Ca2+ entry. Although the
initial stages of this signaling cascade are well known, downstream
events leading to the opening of the TRP channels are still obscure. In
the present study we applied patch-clamp whole-cell recordings and
measurements of Ca2+ concentration by ion-selective
microelectrodes in eyes of normal and mutant Drosophila
to isolate the TRP and TRP-like (TRPL)-dependent currents. We report
that anoxia rapidly and reversibly depolarizes the photoreceptors and
induces Ca2+ influx into these cells in the dark. We
further show that openings of the light-sensitive channels, which
mediate these effects, can be obtained by mitochondrial uncouplers or
by depletion of ATP in photoreceptor cells, whereas the effects
of illumination and all forms of metabolic stress were additive.
Effects similar to those found in wild-type flies were also found in
mutants with strong defects in rhodopsin, Gq-protein, or phospholipase
C, thus indicating that the metabolic stress operates at a late stage of the phototransduction cascade. Genetic elimination of both TRP and
TRPL channels prevented the effects of anoxia, mitochondrial uncouplers, and depletion of ATP, thus demonstrating that the TRP and
TRPL channels are specific targets of metabolic stress. These results
shed new light on the properties of the TRP and TRPL channels by
showing that a constitutive ATP-dependent process is required to keep
these channels closed in the dark, a requirement that would make them
sensitive to metabolic stress.
Key words:
TRP and TRPL channels; Drosophila mutants; anoxia; mitochondrial uncouplers; ion-selective microelectrodes; metabolic stress
Copyright © 2000 Society for Neuroscience 0270-6474/00/20155748-08$05.00/0
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