Kinetics of extracellular ATP hydrolysis by microvascular endothelial cells from rat heart

Abstract

We have characterized the ectonucleotidases that catalyse the reaction sequence ATP-->ADP-->AMP-->adenosine on microvascular endothelial cells cultured from the rat heart. Computer simulation and data fitting of progress of reaction curves showed that depletion of substrate at the cell surface dominates the regulation of the rate of hydrolysis of ATP when it is presented to the cells. Preferential delivery of AMP by ADPase to 5'-nucleotidase makes a significant contribution to the regulation of adenosine production from ATP or ADP. By contrast, we found no evidence for the preferential delivery of ADP from ATPase to ADPase. Feed-forward inhibition of AMP hydrolysis by ADP and/or ATP also modulated the rate of adenosine production. The properties of the ectonucleotidases on rat heart microvascular cells are such that adenosine is produced at a steady rate over a wide range of ATP concentrations.

Adherent Leukocytes Prevent Adenosine Formation and Impair Endothelial Barrier Function by Ecto-5′-nucleotidase/CD73-dependent Mechanism

“…Although these data fit well with the known feed-forward inhibition of endothelial 5Ј-nucleotidase by micromolar concentrations of precursor ATP/ADP (8,26), this inhibitory mechanism is presumably restricted to sites of traumatic tissue injury with massive nucleotide release from the damaged cells and/or dense granules of activated platelets.…”

“…Endothelial E-type NTP-diphosphohydrolases (E-NTPDases, 1 otherwise known as ecto-ATPDase, CD39), in concert with ecto-5Ј-nucleotidase/CD73, represent the important effector system for maintenance of anti-thrombotic and anti-inflammatory state in the vasculature by rapid nucleotide inactivation via stepwise reactions ATP 3 ADP 3 AMP 3 adenosine (8,12,16). The generated adenosine in turn has a non-redundant counteracting role in the attenuation of inflammation and protection from excessive tissue damage in vivo via interaction with its own nucleoside-selective receptors (5,17).…”

Role of A2A‐adenosine receptor activation for ATP‐mediated coronary vasodilation in guinea‐pig isolated heart

“…This suggests that either the densities or subtypes of receptors that mediate responses to ATP are di erent in di erent species, or that di erent rates of metabolism of intravascularly-administered ATP in di erent species may lead to di erent concentrations of ATP at ATP receptors. ATP is rapidly metabolized by endothelial cells in the coronary circulation (Cusack et al, 1983;Pearson & Gordon, 1985;Gordon et al, 1986;Meghji et al, 1995). Therefore during exogenous administration of ATP, the concentration of ATP in the receptor compartment is likely to be much lower than the concentration of ATP in the coronary perfusate.…”

“…it is either transported into cells or degraded by ADA (Meghji et al, 1995;Bruns, 1980;1990). In support of this idea are reports that ecto-5'-nucleotidase, G protein-coupled receptors, and adenylyl cyclase are localized in caveolae (Gordon, 1986;Shaul & Anderson, 1998).…”

The endothelial cell ecto-ADPase responsible for inhibition of platelet function is CD39.

“…Ecto-nucleotidases have now been characterized from a diversity of tissues and species, ranging from insects to parasites to plants and to mammals (6,10,24,25). Substrate specificity of ATPDases varies broadly as individual systems are studied.…”