Light-dependent modulation of Shab channels via phosphoinositide depletion in Drosophila photoreceptors

The Drosophila phototransduction cascade transforms light into depolarizations that are further shaped by activation of voltage-dependent K+ (Kv) channels. In whole-cell recordings of isolated photoreceptors, we show that light selectively modulated the delayed rectifier (Shab) current. Shab currents were increased by light with similar kinetics to the light-induced current itself (latency similar to 20 ms), recovering to control values with at(1/2) of similar to 60 s in darkness. Genetic disruption of PLC beta 4, responsible for light-induced PIP2 hydrolysis, abolished this light-dependent modulation. In mutants of CDP-diaclyglycerol synthase (cds(1)), required for PIP2 resynthesis, the modulation became irreversible, but exogenously applied PIP2 restored reversibility. The modulation was accurately and reversibly mimicked by application Of PIP2 to heterologously expressed Shab channels in excised inside-out patches. The results indicate a functionally implemented mechanism of Kv channel modulation by PIP2 in photoreceptors, which enables light-dependent regulation of signal processing by direct coupling to the phototransduction cascade.