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

Uptake of extracellular adenosine was studied in primary cultures of astrocytes or neurons. Both cell types showed a high affinity uptake. The Km values were not significantly different (6.5 +/- 3.75 microM in astrocytes and 6.1 +/- 1.86 microM in neurons), but the intensity of the uptake was higher in astrocytes than in neurons (Vmax values of 0.16 +/- 0.030 and 0.105 +/- 0.010 nmol x min-1 x mg-1 protein, respectively). The temperature sensitivity was similar in the two cell types. Adenosine uptake inhibitors and benzodiazepines inhibited the adenosine uptake systems in both astrocytes and neurons with IC50 values in the high nanomolar or the micromolar range and the rank order of potency was similar in the two cell types. In both cell types the (-) isomers of two sets of benzodiazepine stereoisomers were more potent than the (+) isomers. Dixon analysis showed that dipyridamole, papaverine, hexobendine and chlordiazepoxide inhibited the adenosine uptake competitively and clonazepam noncompetitively in both cell types.