3-ALPHA-HYDROXY-5-ALPHA-PREGNAN-20-ONE MODULATION OF SOLUBILIZED GABA BENZODIAZEPINE RECEPTOR COMPLEX

The allosteric modulation of the progesterone metabolite 3alpha-hydroxy-5alpha-pregnan-20-one (DHP) on [H-3]Flunitrazepam and [S-35]t-butylbicyclophosphorothionate (TBPS) binding was investigated on a soluble receptor preparation. Better results in the solubilization occurred by the use of the zwitterionic detergent CHAPS with the inclusion of the phospholipid asolectin: this treatment was found suitable to study the steroidal modulation on [H-3]Flunitrazepam and [S-35]TBPS binding. We found that DHP was able to enhance [H-3]Flunitrazepam binding in the presence of Cl ions, while [S-35]TBPS binding was inhibited by DHP. Scatchard analysis of specific [S-35]TBPS and [H-3]Flunitrazepam binding yielded in a single straight line both in the controls and in the presence of the hormone: DHP increased the apparent affinity of [H-3]Flunitrazepam binding without altering the apparent B(max) value. In the case of [S-35]TBPS, DHP decreased the apparent B(max) value whereas the K(d) value remained nearly the same.