EAG channels expressed in microvillar photoreceptors are unsuited to diurnal vision

摘要

Key points class="unordered" style="list-style-type:disc" id="tjp12219-list-0001">The principles underlying the evolutionary selection of ion channels for expression in sensory neurons are unclear.Photoreceptor depolarization in the diurnal Drosophila melanogaster is predominantly provided by light‐activated transient receptor potential (TRP) channels, whereas repolarization is mediated by sustained voltage‐gated K⁺ channels of the Shab family.In the present study, we show that phototransduction in the nocturnal cockroach Periplaneta americana is predominantly mediated by TRP‐like channels, whereas membrane repolarization is based on EAG channels.Although bright light stimulates Shab channels in Drosophila, further restricting depolarization and improving membrane bandwidth, it strongly suppresses EAG conductance in Periplaneta. This light‐dependent inhibition (LDI) is caused by calcium and is abolished by chelating intracellular calcium or suppressing eag gene expression.LDI increases membrane resistance, augments gain and reduces the signalling bandwidth. This makes EAG unsuitable for light response conditioning during the day and might have resulted in the evolutionary replacement of EAG by other delayed rectifiers in diurnal insects.