gamma-Aminobutyric acid and glycine activate Cl- channels having different characteristics in CNS neurones.

We have studied the properties of Cl- channels in Müller cells of the lamprey brain, which are activated by two putative neurotransmitters, glycine and gamma-aminobutyric acid (GABA). Previous studies have shown that in these cells the two ligands act through different receptors, and it was of interest to determine whether or not the two receptors, in turn, activate separate channels having different properties. We have shown previously that the channels activated by glycine have large conductances which decrease rapidly as the intracellular Cl- concentration [Cl-]i is increased above normal. We show here that GABA-activated channels have much smaller conductances which are independent of [Cl-]i over the experimental range and also that the response to a saturating application of glycine is not occluded by simultaneous GABA application. These observations indicate that the glycine and GABA receptors are coupled to separate Cl- channels having different characteristics.