Temperature dependence and GABA modulation of [ 3H]triazolam binding in the rat brain

Abstract

The hypnotic triazolam (TZ), a triazolobenzodiazepine displays a short physiological half life and has been used for the treatment of insomnia related to anxiety states. Our major objectives were the direct measurement of the temperature dependence and the gamma-aminobutyric acid (GABA) effect of [ 3H]TZ binding in the rat brain. Saturation studies showed a shift to lower affinity with increasing temperatures (K d = 0.27±08 nM at 0°C; K d = 1.96±0.85 nM at 37°C) while the B max values remained unchanged (1220±176 fmoles/mg protein at 0°C and 1160±383 fmoles/mg protein at 37°C). Saturation studies of [ 3H]TZ binding in the presence or absence of GABA (100uM) showed a GABA-shift. At 0°C the K d values were (K d=0.24±0.03 nM/−GABA; K d=0.16±0.04/+GABA) and at 37°C the K d values were (K d=1.84±0.44 n/M−GABA; K d=0.95±0.29 n/M+GABA). In contrast to reported literature, our findings show that TZ interacts with benzodiazepine receptors with a temperature dependence and GABA-shift consistent with predicted behavior for benzodiazepine agonists.