TRP channels in visual transduction

Abstract

The original members of the superfamily of transient receptor potential channels are the TRP and TRPL channels underlying Drosophila light transduction. Light transduction takes place in the photosensitive microvilli within the photoreceptor cells; it is initiated by photon absorption which leads ultimately to the generation of a depolarizing receptor potential caused by TRP and TRPL channel opening. Channel opening is mediated by a phospholipase C pathway where the membrane second messenger diacylglycerol appears to be the channel activator. TRP is a Ca2+ selective channel responsible for nearly 95 % of the net transduction current, whereas TRPL, a poorly-selective Ca2+ channel, accounts for the difference. The scaffolding protein INAD forms a complex with TRP and other transduction proteins, offering an extremely fast transduction mechanism. TRP and TRPL are also found in the synaptic terminals of the photoreceptors, where they play a role in presynaptic Ca2+ increments during synaptic transmission.