In the mammalian central nervous system, glycine and γ-aminobutyric acid (GABA) bind to specific and distinct receptors1-4 and cause an increase in membrane conductance to Cl- (refs 5-7). Neurones in various regions of the nervous system show differential sensitivity to glycine and GABA2,3; thus GABA and glycine receptors are spatially distinct from one another. However, on the basis of desensitization experiments on spinal cord neurones, it was suggested that the receptors for glycine and GABA may share the same Cl- channel8. We now report that in small membrane patches, isolated from the soma of spinal neurones, both receptor channels display several (multiple) conductance states. Two of the states are common to both receptor channels. However, the most frequently observed 'main conductance states' of the GABA and glycine receptor channels are different. Both channels display the same anion selectivity. We propose that one class of multistate Cl-channel is coupled to either GABA or glycine receptors. The main conductance state adopted by this channel is determined by the receptor to which it is coupled.
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