Critical Evaluation of the Role of Ecto- and Cytosolic 5′-Nucleotidase in Adenosine Formation

Abstract

Inhibition of ecto-5′-nucleotidase with an antiserum failed to inhibit adenosine formation in rat polymorphonuclear leucocytes or neonatal heart cells in culture. Adenosine accumulated in the cytoplasm and was exported by the dipyridamole-sensitive nucleoside transporter. Adenosine formation in polymorphonuclear leucocytes was accounted for by the activity of the cytoplasmic 5′-nucleotidase, the low activity of which in rat erythrocytes was associated with reduced capacity to hydrolyse AMP. Globally-ischaemic pigeon hearts produced adenosine rapidly despite the virtual absence of ecto-5′-nucleotidase activity. An ATP-activated 5′-nucleotidase, sufficiently active to account for adenosine fourmation, was present in the soluble fraction of pigeon ventricle. The data suggest that a cytoplasmic 5′-nucleotidase provides the biochemical link between cellular ATP breakdown and adenosine formation.