A comparison of the effects of midazolam and pentobarbital on the dose-response of GABA-gated Cl- influx in rat brain microsacs.

gamma-Aminobutyric acid (GABA)-gated Cl- influx was studied in a rat brain 'microsac' preparation. Midazolam (a benzodiazepine), at 0.1-10 microM, increased GABA potency (maximum 2-fold) without affecting its efficacy or exerting GABA-mimetic effect. Pentobarbital (10-500 microM) increased GABA potency (maximum 12-fold) and efficacy (maximum 40%). Pentobarbital exhibited GABA-mimetic effect at concentrations above 200 microM. The differential effects of midazolam and pentobarbital in modulating GABA-mediated responses may account for some of the differences between these two classes of drugs.