In the mouse retina, the reversal potential of Cl^-(E_Cl) is different between ON- and OFF- bipolar cells. The difference of E_Cl favors for the hypothesis that the difference of the reversal potential of GABA responses (E_GABA) produces the opposite polarity of surround responses between ON- and OFF-bipolar cells. Another line of evidence shows that the expression patterns of the GABA_A and GABA_C receptors are different among bipolar cells subtypes. However, it has not been studied whether such a differences of the expression patterns of GABA receptor subtypes can contribute to the difference of E_GABA, since E_GABA is determined by the combination of E_Cl and the reversal potential of HCO₃^-. In the present study, we examined a possibility that the differences of permeability to HCO₃^-in GABA receptor subtypes are involved in the determination of E_GABA by the whole cell patch clamp technique. We also examined whether current hypothesis is sufficient to explain the opposite polarity of surround responses by perforated patch clamp techniques. The reversal potential of GABA_A and GABA_C receptors were not different in the presence (GABA_A: -4.5±5.7 mV, n=6; GABA_C: -2.6±3.4 mV, n=5) and the absence (GABA_A: -5±3.5 mV, n=6; GABA_C: -3.8±4.8 mV, n=5) of extracellular HCO₃^-(24 mM). We found that the E_Cl of soma(-18±7.5 mV, n=6) was higher than that of axon terminal(-42±6.2 mV, n=6) in rod bipolar cells. The intracellular Cl^-concentration gradient was disappeared and E_Cl shifted to negative direction (-57±4.3 mV, n=3) when 50µM bumetanide, a NKCC1 antagonist, were applied. These results show that the differences in the distribution of GABA receptor subtypes and the permeability of HCO₃^- do not contribute to the polarity determination of the surround responses of the bipolar cells, rather that the intracellular Cl^-concentration controlled by the Cl^-transporter determines the polarity of surround responses.