BOVINE ADRENAL ENDOTHELIAL-CELLS EXPRESS NUCLEOSIDE TRANSPORTERS NONREGULATED BY PROTEIN-KINASE-A AND PROTEIN-KINASE-C

The present investigation characterizes the nucleoside transporters in bovine adrenomedullary endothelial cells and their possible regulatio n by the action of protein kinases A and C to establish comparisons wi th the nucleoside transport, system in chromaffin cells. The nucleosid e transport proved to be a nitrobenzylthioinosine (NBTI)-sensitive fac ilitated-diffusion system with high affinity for adenosine. These endo thelial cells had a high density of nucleoside transporters (660,000 /- 130,000 transporters/cell), measured by NBTI binding, and the effic iency was close to 2 adenosine molecules internalized . transporter(-1 ). s(-1). The stimulation of the cells with bradykinin and P-1,P-4-di( adenosine-5')tetraphosphate, which raise the intra cellular Ca2+ conce ntration, did not modulate the adenosine transport. When the cells wer e stimulated with signals coupled to adenosine 3',5'-cyclic monophosph ate intracellular production, such as norepinephrine and isoproterenol , the adenosine transport was not modified. Furthermore, the treatment of the cells with direct activators of both protein kinases A and C h ad no effect on adenosine transport, in contrast to that reported in c hromaffin cells.