Abstract
Invertebrate phototransduction is an important model system for studying the ubiquitous inositol-lipid signaling system. In the transient receptor potential ( trp) mutant, one of the most intensively studied transduction mutants of Drosophila, the light response quickly declines to baseline during prolonged intense light. Using whole-cell recordings from Drosophila photoreceptors, we show that the wild-type response is mediated by at least two functionally distinct classes of light-sensitive channels and that both the trp mutation and a Ca 2+ channel blocker (La 3+) selectively abolish one class of channel with high Ca 2+ permeability. Evidence is also presented that Ca 2+ is necessary for excitation and that Ca 2+ depletion mimics the trp phenotype. We conclude that the recently sequenced trp protein represents a class of light-sensitive channel required for inositide-mediated Ca 2+ entry and suggest that this process is necessary for maintained excitation during intense illumination in fly photoreceptors.
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