Size and chirality of intracellularly applied anions affect the function of isolated photoreceptors

The effect of intracellularly applied anions on the function of retinal rods of the frog Rana esculenta was investigated by means of the whole-cell patch-clamp technique. When the recording pipette contained a medium based on potassium chloride, a slow spontaneous hyperpolarization was observed presumably due to a diffusional loss of the photoreceptor's internal transmitter cyclic guanosine monophosphate (cGMP) and its precursor guanosine triphosphate (GTP). When chloride was replaced by organic anions such as acetate, aspartate, or gluconate the speed of hyperpolarization diminished and the dark voltage of the rods was stabilized. The extent of stabilization correlates with the molecular weight of the anions. A significant difference in the stabilizing effect was found for L-aspartate and D-aspartate, suggesting an additional influence of the chirality. Effects of some of the anions on the configuration of the light responses were also observed.