Similarities of adenosine uptake systems in astrocytes and neurons in primary cultures

Adenosine potentiation and antagonism may account for the diverse behavioral actions of Ro 5-4864

The actions of the p-chloroderivative of diazepam, Ro 5-4864 on the spontaneous discharges of rat cerebral cortical neurons and its interactions with depressions evoked by adenosine and adenosine 5'-N-ethylcarboxamide (NECA) were observed. Iontophoretically applied Ro 5-4864 had variable actions on cortical neuronal activity, exciting some neurons and depressing others. During the period of applications. Ro 5-4864 antagonized the depressant effects of NECA, whilst having less of an action on adenosine depressions. Following Ro 5-4864 application adenosine, but not NECA, depressions were potentiated in amplitude and duration for periods of up to 20 min. It is suggested that Ro 5-4864 has both antagonistic and potentiative interactions with adenosine.

Dissimilarities between benzodiazepine-binding sites and adenosine uptake sites in astrocytes and neurons in primary cultures

The question whether the benzodiazepine receptor site in astrocytes or in neurons might be identical to the adenosine uptake site was studied by determining pharmacological profiles, inhibition types, and the effects of benzodiazepine antagonists in primary cultures of either astrocytes or neurons. Fourteen different benzodiazepines and five different adenosine uptake inhibitors displaced [3H] diazepam and inhibited adenosine uptake in both astrocytes and neurons. However, the rank orders (determined as IC50 values) with which these two parameters were affected were profoundly different, indicating dissimilarities between these two sites. For several of the compounds a difference in inhibition type (competitive vs. noncompetitive) was observed between the benzodiazepine-binding site and the adenosine uptake site in astrocytes and/or neurons, which further corroborated the conclusion of a difference between the benzodiazepine-binding site and the adenosine uptake site. Finally, the neuronal benzodiazepine antagonists RO 15-1788 and CGS-8216 and the astrocytic benzodiazepine antagonist PK 11195, which reverse the action of benzodiazepines, were not able to reverse inhibition of adenosine uptake by diazepam but exerted an inhibitory effect of their own.