The Journal of General Physiology
Avanti Polar Lipids
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Published online December 26, 2006
doi:10.1085/jgp.200609659
The Journal of General Physiology, Vol. 129, No. 1, 17-28
The Rockefeller University Press, 0022-1295 $30.00
© 2006 Parnas et al.
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ARTICLE

 Open Channel Block by Ca2+ Underlies the Voltage Dependence of Drosophila TRPL Channel



Moshe Parnas, Ben Katz, and Baruch Minke

Department of Physiology and the Kühne Minerva Center for Studies of Visual Transduction, Faculty of Medicine, Hebrew University, Jerusalem 91120, Israel

Correspondence to Baruch Minke: minke{at}md.huji.ac.il

The light-activated channels of Drosophila photoreceptors transient receptor potential (TRP) and TRP-like (TRPL) show voltage-dependent conductance during illumination. Recent studies implied that mammalian members of the TRP family, which belong to the TRPV and TRPM subfamilies, are intrinsically voltage-gated channels. However, it is unclear whether the Drosophila TRPs, which belong to the TRPC subfamily, share the same voltage-dependent gating mechanism. Exploring the voltage dependence of Drosophila TRPL expressed in S2 cells, we found that the voltage dependence of this channel is not an intrinsic property since it became linear upon removal of divalent cations. We further found that Ca2+ blocked TRPL in a voltage-dependent manner by an open channel block mechanism, which determines the frequency of channel openings and constitutes the sole parameter that underlies its voltage dependence. Whole cell recordings from a Drosophila mutant expressing only TRPL indicated that Ca2+ block also accounts for the voltage dependence of the native TRPL channels. The open channel block by Ca2+ that we characterized is a useful mechanism to improve the signal to noise ratio of the response to intense light when virtually all the large conductance TRPL channels are blocked and only the low conductance TRP channels with lower Ca2+ affinity are active.

M. Parnas and B. Katz contributed equally to this work.

Abbreviations used in this paper: CaM, calmodulin; CNG, cyclic nucleotide-gated; LIC, light induced current; S2, Schneider 2 cells; TRP, transient receptor potential; TRPL, TRP-like.


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