The pH dependence of the receptor potential of the hermit crab photoreceptor.

The pH dependence of the receptor potential (ReP) of isolated layers of photoreceptor cells from the hermit crab compound eye (Eupagurus bernhardus L.) was determined. Measurements were performed, using extracellular electrodes, in the range pH 3.5 —9.5 in three different buffer systems: Tris, glycine, and phosphate. The amplitude of the ReP was highest at pH 7.5 and decreased in more acidic and more alka­ line salines (Fig. 4). Relative to the changes in ReP amplitude, the changes in time course and shape of ReP were small. Salines of pH other than 7.5 caused an increase of the latent period but decreased the peak amplitude time and the repolarizing phase (i2). Alkaline salines caused about the same changes in the ReP as acidic salines. The only observed difference was that repolarisation was more strongly influenced by alkaline solutions and that the plateau magnitude was depressed relatively more than the peak magnitude in acidic environments. Of the three buffers used, Tris had the weakest influence on the ReP and phosphate buffer the strongest. In contrast to the good reproducibility of the experimental results, the reversibility of the pH effects was generally poor; the effects with glycine-buffer were more reversible than those with Tris.