Intracellular chloride concentration is higher in rod bipolar cells than in cone bipolar cells of the mouse retina.

Bipolar cells (BCs) have antagonistic center-surround receptive field. Surround illumination evokes depolarization in the OFF-type cone BC, and hyperpolarization in the rod BC and the ON-type cone BC. Surround illumination reduces gamma-aminobutyric acid (GABA) release from horizontal cells. If GABA hyperpolarize BCs, the polarity of the GABA-induced effect agrees with the light-evoked surround response in the OFF-type BC, but contradicts in the rod BC and the ON-type cone BC. Immunohistochemical study of the Cl(-) transporter of BCs has suggested that the intracellular Cl(-) concentration is different among BC subtypes. We examined the reversal potential of GABA-induced current of BCs using gramicidin-perforated patch clamp technique in the mouse retina, and found that GABA depolarizes rod BC and hyperpolarizes cone BCs. Our results are consistent with the GABAergic input to rod BC dendrite.