Adenosine transport into guinea-pig synaptosomes.

Kinetics for transport of adenosine into guinea-pig neocortex synaptosomes were studied by incubating them with [14C]adenosine for up to 30 s. The apparent Km value of the high-affinity transport system for adenosine was 21.1 microM and the Vmax value was 257.3 pmol/min/mg protein. The transport system was inhibited by both compounds structurally related (compounds 554 and 555) and unrelated (dipyridamole) to adenosine. Because electrically stimulated synaptosomes release up to 1.5% of the adenosine derivative content per min, the physiological significance of adenosine uptake is discussed as a possible mechanism to compensate for the loss of adenine nucleotides from synaptosomal preparations.