Abstract
The effects of barbiturates on the GABA-receptor complex and the A1
adenosine receptor were studied. At the GABA-receptor complex the
barbiturates inhibited the binding of 35St-butylbicyclophosphorothionate
(35STBPT) and enhanced the binding of 3Hdiazepam. Kinetic and
saturation experiments showed that both effects were allosteric.
Whereas all barbiturates caused complete inhibition of 35STBPT
binding, they showed varying degrees of maximal enhancement of 3Hdiazepam
binding; (+/-)methohexital was identified as the most efficacious
compound for this enhancement. At the A1 adenosine receptor all barbiturates
inhibited the binding of 3HN6-phenylisopropyladenosine (3HPIA)
in a competitive manner. The comparison of the effects on 3Hdiazepam
and 3HPIA binding showed that excitatory barbiturates interact
preferentially with the A1 adenosine receptor, and sedative/anaesthetic
barbiturates with the GABA-receptor complex. It is speculated that
the interaction with these two receptors might be the basis of the
excitatory versus sedative/anaesthetic properties of barbiturates.
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