Ethanol-induced extension of screening-pigment migration range in crayfish photoreceptors

Abstract

1. Ethanol 5–10% extends the normal range of screening-pigment migration along the photoreceptors of crayfish compound eyes, the effect being accounted for by a supramaximal pigment aggregation in the dark. 2. Excised eyes incubated in the presence of ethanol showed a faster and enhanced pigment aggregation to the dark-Actapted position, whereas the kinetics of the reverse movement in response to illumination was little affected. Methanol and propanol also facilitated pigment aggregation, although not with the same effectiveness as ethanol at equivalent concentrations. 3. The ethanol-induced facilitation of pigment aggregation persisted for some time after thorough washing of the eyes, and counteracted the inhibition of dark-Actaptation normally caused by an increaScin temperature. 4. Two possible explanations for this peculiar effect of ethanol are discussed: (a) alterations in photoreceptor membrane permeability that, in turn, may affect the ionic mechanisms controlling pigment position; and (b) promotion of local release of neurotransmitters involved in the modulation of light/dark adaptation.