The effects of temperature and light on particles associated with crayfish visual membrane: a freeze-fracture analysis and electrophysiological study

Abstract

Depending on the pre-experimental treatment, densities as well as sizes of particles associated with the visual membranes in the eyes ofProcambarus clarkii varied. The highest mean particle density (5268 ± 969 μm²) and the smallest mean particle diameter (5.57 ± 1.35 nm) were found in crayfish which had been kept in the dark for 10 weeks in aerated fresh water of 10 ° C. Crayfish kept under a 12 h dark/light regime in water of 10 ° C or 30 ° C for three weeks displayed particle densities of 1076 ± 180 and 2899 ± 249 μm⁻², respectively; particle diameters were of the order of 8 nm. Temperature did not alter the shape or the slope of theV/logI curves, but ERG recordings show that maximum spectral sensitivity was shifted from λ_max=560 nm in cold water crayfish (10 ° C) to λ_max=580 nm in crayfish from the 30 ° C tank, and that the 10 ° C curve was somewhat narrower than the 30 ° C curve. It is suggested that the observed shift was caused by a combination of factors, of which the following may have played key roles: (1) The filter effect of screening pigment granules and other intracellular components such as vesicles, vacuoles, endoplasmic reticulum, and mitochondria, some of which were developed to a considerably greater extent in 30 ° C material; (2) increased membrane fluidity due to higher temperature as well as the presence of photoproducts in the light, and the ‘countermeasures’ taken by the visual pigment molecules to stabilize the lipid bilayer, e.g. higher density, possible 12-s-cis linkages etc.; and (3) increased regeneration or synthesis of rhodopsin due to higher metabolic activity of retinula cells at higher temperatures. Temperature-induced changes of visual pigments in a variety of organisms are discussed and evidence for the rhodopsin-aggregate model of crayfish visual pigment is presented. It is concluded that the retinula cytoplasm is involved in restoring depleted stocks of photopigment, and that the biological sense of possessing an increase in red sensitivity during the warm summer months lies in the correlation of light penetration in the natural habitat ofP. clarkii and optimal exploitation of the habitat.