Solubilization andcharacterization ofGABABreceptor binding sites fromporcine brain synaptic membranes

sulphonate (CHAPS)(0.5%) provedtobethemostsuccessful, solubilizing 22.7 ±4.7%(mean±s.e.mean, n=6)ofGABABreceptors. 3 Binding of[3H]-GABA toGABABreceptors solubilized with0.5%CHAPSexhibited similar characteristics tothebinding atmembrane boundreceptors since, firstly, theKdandBm,, values (around 30nM and450fmolmg- protein, respectively) werecomparable; secondly, stereospecific binding forbaclofen wasobtained inbothforms; thirdly, theaffinity fortheagonists GABA and(-)-baclofen andthe antagonists CGP35348, CGP36742andCGP54626werethesame;fourthly, comparable sensitivity to Ca2`(2.5 mM)wasobserved andfinally, asimilar sensitivity toGTP wasapparent. 4 Saturation experiments performed withtheGABABantagonist, [3H]-CGP 54626, indicated ahigher Kdvalueanda lowerBma, valueforsolubilized (7.7 ±2.6nM and1033±41fmolmg-'protein, mean±s.e.mean, n= 3)thanformembraneboundreceptors (1.35 ±0.08 nM,1171±20fmolmg' protein, n=3).