Activation of GABA rho 1 receptors by glycine and beta-alanine

Neurons of the vertebrate retina possess receptors for many neurotransmitters. Particularly interesting is a new type of GABA receptor (GABA rho) that, in contrast to GABAA and GABAB receptors, shows very little desensitization, is not blocked by bicuculline, and is not activated by baclofen. Homomeric human GABA rho 1 receptors were expressed in Xenopus oocytes. In addition to GABA, and related agonists, GABA rho 1 receptors respond to glycine (Gly) and beta-alanine (beta-Ala) by generating Cl- currents that do not desensitize and are resistant to bicuculline. The half-maximal concentrations for Gly and beta-Ala currents were 14.2 +/- 1.3 mM and 0.66 +/- 0.11 mM respectively. The current responses to Gly and beta-Ala were blocked by picrotoxin and TBPS. The cross-sensitivity of GABA rho 1 receptors to Gly and beta-Ala may play a role in retinal physiology.