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Interactions Between Light-Induced Currents, Voltage-Gated Currents, and Input Signal Properties in Drosophila Photoreceptors

¹Physiological Laboratory, University of Cambridge, Cambridge CB2 1TN, United Kingdom; ²Division of Biophysics, Department of Physical Sciences, University of Oulu, Oulu, FIN-90014, Finland; and ³Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada

Submitted 4 December 2003; accepted in final form 21 January 2004

Voltage-gated K⁺ channels are important in neuronal signaling, but little is known of their interactions with receptor currents or their behavior during natural stimulation. We used nonparametric and parametric nonlinear modeling of experimental responses, combined with Hodgkin–Huxley style simulation, to examine the roles of K⁺ channels in forming the responses of wild-type (WT) and Shaker mutant (Sh¹⁴) Drosophila photoreceptors to naturalistic stimulus sequences. Naturalistic stimuli gave results different from those of similar experiments with white noise stimuli. Sh¹⁴ responses were larger and faster than WT. Simulation indicated that, in addition to eliminating the Shaker current, the mutation changed the current flowing through light-dependent channels [light-induced current (LIC)] and increased the delayed rectifier current. Part of the change in LIC could be attributed to direct feedback from the voltage-sensitive ion channels to the light-sensitive channels by the membrane potential. However, we argue that other changes occur in the light detecting machinery of Sh¹⁴ mutants, possibly during photoreceptor development.

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