Voltage-activated potassium channels (Kv channels) in the microvillar photoreceptors of arthropods are responsible for repolarization and regulation of photoreceptor signaling bandwidth. On the basis of analyzing Kv channels in dipteran flies it was suggested that diurnal, rapidly-flying insects predominantly express sustained potassium conductances, whereas crepuscular and nocturnally active animals exhibit strongly inactivating Kv conductances. The latter was suggested to function for minimizing cellular energy consumption. Here we further explore the evolutionary adaptations of the photoreceptor channelome to visual ecology and behavior by comparing potassium conductances in fifteen phylogenetically diverse insects, using patch-clamp recordings from dissociated ommatidia. We show that rapid diurnal flyers such as the blowfly Calliphora vicina and the honeybee Apis mellifera express relatively large non-inactivating Kv conductances, conforming to the earlier hypothesis in Diptera. Nocturnal and/or slow moving species do not in general exhibit stronger Kv conductance inactivation in the physiological membrane voltage range, but the photoreceptors in species that are known to rely more on vision behaviourally had higher densities of sustained Kv conductances than photoreceptors of less visually-guided species. No statistically significant trends related to visual performance could be identified for the rapidly inactivating Kv conductances. Counter-intuitively, strong negative correlations were observed between photoreceptor capacitance and specific membrane conductance for both sustained and inactivating fractions of Kv conductance, suggesting insignificant evolutionary pressure to offset negative effects of high capacitance on membrane filtering with increased conductance.
- insect photoreceptor
- potassium channels
- compound eye
- visual ecology
- Copyright © 2015, Journal of Neurophysiology