Uptake of adenosine by isolated rat brain capillaries.

Adenosine uptake by isolated rat brain capillaries is a carrier-mediated, temperature- and pH-sensitive process. The Km value for adenosine uptake is 4.74 microM and the Vmax is 21.7 picomol/mg protein/10 min. This is a high-affinity uptake system that can be cross-inhibited by several nucleosides and by the adenosine analogs tubercidin and 5'-deoxyadenosine. The uptake is very sensitive to inhibition by papaverine, hexobendine, and dipyridamole. These results confirm the existence of a nucleoside transport system associated with the blood-brain barrier observed during in vivo studies.