Sen RP, Delicado EG, Castro E, Miras-Portugal MT. Effect of P2Y agonists on adenosine transport in cultured chromaffin cells.
J Neurochem 1993;
60:613-9. [PMID:
8419539 DOI:
10.1111/j.1471-4159.1993.tb03192.x]
[Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Adenosine transport in cultured chromaffin cells was inhibited by purinergic P2y-receptor agonists without significant changes in the affinity constant, the values being between 1 +/- 0.4 and 1.6 +/- 0.6 microM. The Vmax parameter was modified significantly, being 40 +/- 1.0, 26 +/- 5.0, 32 +/- 3.0, and 22 +/- 4.7 pmol/10(6) cells/min for control, adenosine-5'-O-(2-thiodiphosphate), 5'-adenylylimidodiphosphate, and P1,P4-di(adenosine-5'-) tetraphosphate (Ap4A) (100 microM for every effector), respectively. Ap4A, a physiological ligand for P2y receptors in chromaffin cells, showed the highest inhibitory effect (45%). This transport inhibition is explained by an increase in the cytosolic Ca2+ concentration ([Ca2+]i) and the activation of protein kinase C (PKC). Experiments of [Ca2+]i measurement with the fura-2 technique showed that P2y agonists, as well as bradykinin, were able to increase [Ca2+]i, this effect being independent of the presence of extracellular Ca2+. The peptide bradykinin, determined to be coupled to phosphatidylinositol hydrolysis and internal Ca2+ mobilization in chromaffin cells, exhibited a behavior similar to that of P2y agonists in adenosine transport inhibition (39%). P2y agonists and bradykinin increased PKC activity associated with the membrane fraction (about 50% increase in particulate PKC activity with respect to controls). The present studies suggest that adenosine transport is regulated by P2y-purinergic receptors mediated via Ca2+ mobilization and PKC activation.
Collapse