ABSTRACT
The development of the GABA system in the rabbit retina was studied. The number of high- and low-affinity GABA receptor binding sites increased in a sigmoidal manner, with the curve for the low-affinity sites lagging 2-3 days behind that for the high-affinity sites. The KD for both high- (17.5 nM) and low-affinity (138.0 nM) sites remained constant during development. Treatment of isolated eyecups with the uptake blocker nipecotic acid resulted in an increase in the Bmax for high-affinity sites in developing tissue with the maximum sensitivity around eye opening; mature tissue exhibited a decrease in Bmax. In contrast, a gradual decrease in sensitivity to stimulation of the low-affinity sites occurred. These data indicate that the "trophic" action of GABA is limited to the time when the tissue is developing.
Subject(s)
Nipecotic Acids/pharmacology , Proline/analogs & derivatives , Receptors, GABA-A/analysis , Retina/analysis , Age Factors , Animals , Animals, Newborn , Rabbits , Retina/growth & developmentABSTRACT
The sensitivity of [(3)H]GABA and [(3)H]muscimol high-affinity binding sites to physiological (Krebs-Ringer's bicarbonate) and non-physiological (Tris-citrate) buffers was examined using synaptosomal membranes from bovine retinas. The maximum number of sites (B(max)) for [(3)H]GABA was present when the tissue was assayed in KRB. With only one exception, this effect was independent of the washing conditions used or a small change in pH. In contrast, [(3)H]muscimol binding sites were maximally present when the tissue was washed in Tris, regardless of the assaying conditions or the small change in pH. Neither [(3)H]GABA nor [(3)H]muscimol was displaced by ( - )baclofen. The apparent dissociation constants (K(d)) of the ligands did not change under any of the conditions tested. These findings demonstrate a fundamental difference between GABA and muscimol binding sites.
