Selective photoinduced Ca2+ diffusion in rhodopsin–lipid bilayers: an internal transmitter hypothesis

Abstract

Triton X-100 purified rhodopsin has been incorporated into lipid bilayer membranes prepared by the combined lifting-and-touching method. The illumination of the membranes with white light and monochromatic light of λ = 498 nm resulted in a high selective increase of Ca2+ diffusion through the lipid bilayers compared to Na+ and K+. The stoichiometric ratios of photoinduced ion diffusion were found to be more than 888 Ca2+ Rh*−1 s−1 and 166 Na+ Rh*−1 s−1 at 290 K using the white light, and 1 277 Ca2+ Rh*−1 s−1, 96 K+ Rh*−1 s−1, and 50 Na+ Rh*−1 s−1 at 276 K using the monochromatic light. It was inferred that Ca2+ is an excellent candidate as internal transmitter in the visual photo-transduction.