Abstract

Retinal ON-bipolar cells possess a metabotropic glutamate receptor linked to the control of a cGMP cascade, which functions to generate high synaptic amplfication of rod signals under darkadapted conditions. We report that a major component of light adaptation of the rod visual system results from a reduction in gain in synaptic transmission from rods to ON-bipolar cells, initiated by Ca²⁺-loading when the cGMP-activated channels of the postsynaptic cell open with light. When intracellular Ca²⁺-buffering was reduced adaptation was induced in ON-bipolar cells by background light too weak to significantly desensitize rods, a property absent in OFF-bipolar cells. Desensitization of ON-bipolar cell flash responses was induced by raising intracellular free Ca²⁺. (Keio J Med 48 (3): l40-l46, September 1999)

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