Ion and temperature effects on the binding of gamma-aminobutyrate to its receptors and the high-affinity transport system.
A set of procedures was developed to study the binding of gamma-[3H]aminobutyric acid ([3H]GABA) to GABAA and GABAB receptors, and to the Na(+)-dependent transport carrier, at 25 and 37 degrees C in the presence of physiological concentrations of Na+. The membrane preparation used in these procedures was not subjected to freeze-thawing or treatment with Triton X-100. Isoguvacine, (-)-baclofen, and (-)-nipecotate were used to block selectively the binding to GABAA receptors, GABAB receptors, and the transport site, respectively. Analysis of the binding characteristics of [3H]GABA to the GABAA receptor suggested the existence of high-(KD less than 30 nM), middle- (KD = 100-500 nM), and low-affinity (KD greater than 5 microM) binding sites. However, the binding data in the middle-affinity region (100-1,000 nM) were often indicative of cooperativity. The affinity between GABA and the GABAA receptor was reduced modestly by increases in temperature and by the presence of Cl- at physiological concentrations. Binding to the GABAB receptor required Ca2+ and Cl-. Apparent binding to the transport carrier required both Na+ and Cl-. A comparison of Bmax values in three brain regions revealed an inverse relationship between the high-affinity site of the GABAA receptor and the transport binding site.
Shank
R P
RP
Department of Biological Research, Janssen Research Foundation, Spring House, PA 19477-0776.
Baldy
W J
WJ
Mattucci
L C
LC
Villani
F J
FJ
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001692:Biological Transport; D002118:Calcium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology*; D007477:Ions; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D051381:Rats; D011963:Receptors, GABA-A / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology*; D013696:Temperature; D005680:gamma-Aminobutyric Acid / Q000031:analogs & derivatives / Q000378:metabolism*
D002712:Chlorides; D007477:Ions; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D012964:Sodium; D002118:Calcium