An anion channel was incorporated from rat brain synaptic plasma membrane fractions into planar lipid bilayers. The single-channel conductance was found to be 48.5 pS in choline-Cl solution (300 μM cis/100 μM trans). The anion selectivity of the channel was rather low (P(Cl)/P(choline) = 1.7). The gating rate of the channel did not change with membrane potential over the range of -50 mV to 50 mV. Several drugs, which are known as inhibitors of anion channels, were found to be efficient inhibitors for the synaptosomal anion channel. 4-Acetoamino-4'-isothiocyanoatilbene-2,2'-disulfonic acid, ethacrynic acid, indanyloxyacetic acid, and 5-nitro-2-(3-phenylpropylamino) benzoic acid inhibited the channel from the cis side of the membrane, corresponding to the cytoplasmic side of the plasma membrane. We found that the channel is regulated by intracellular ATP at millimolar concentrations. Other nucleotides, ADP and GTP, inhibited the channel as well. Glibenclamide, which is known as an inhibitor of an ATP-regulated potassium channel, inhibited the channel at micromolar concentrations from the trans side of the membrane. It is likely that the synaptosomal anion channel is a member of the ATP-binding cassette superfamily.
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