IN-VIVO ANALYSIS OF THE DROSOPHILA LIGHT-SENSITIVE CHANNELS, TRP AND TRPL

We have tested the proposal that the right-sensitive conductance in Dr osophila is composed of two independent components by comparing the wi ld-type conductance with that in mutants lacking one or the other of t he putative light-sensitive channel subunits, TRP and TRPL. For a wide range of cations, ionic permeability ratios in wild type were always intermediate between those of trp and trpl mutants. Effective channel conductances derived by noise analysis in wild type were again interme diate (17 pS; c.f. 35 pS in trp and 4 pS in trpl) and also showed a co mplex voltage dependence, which was quantitatively explained by the su mmation of TRPL and TRP channels after taking their different reversal potentials into account. Although La3+ partially blocked the light re sponse in wild-type photoreceptors, it increased the effective single channel conductance. The results indicate that the wild-type light-act ivated conductance is composed of two separate channels, with the prop erties of TRP-and TRPL-dependent channels as determined in the respect ive mutants.