Kinetic characterization of ATP diphosphohydrolase and 5′‐nucleotidase activities in cells cultured from submandibular salivary glands of rats

Abstract

The participation of ecto-ATP diphosphohydrolase (CD39; ecto-NTPDase) and ecto-5'-nucleotidase (CD73) activities in the nucleotide hydrolysis by salivary gland cells from rats was evaluated. We investigated the biochemical characteristics of these ectoenzymes in cells cultured from submandibular salivary glands of rats. The V(max) for the hydrolysis of ATP, ADP and AMP were 2275+/-153 (mean+/-SEM, n = 4), 941+/-96 (mean+/-SEM, n = 5) and 175+/-5 (mean+/-SEM, n = 5) nmol Pi liberated per min per mg of protein, respectively. The K(m) values for ATP, ADP and AMP were 224+/-8 microM (mean+/-SEM, n = 4), 163+/-15 microM (mean+/-SEM, n = 5) and 117+/-5 microM (mean+/-SEM, n = 5), respectively. The competition plot showed that ATP and ADP were hydrolyzed at the same active site on the enzyme. It may be postulated that the physiological role for this ecto-enzyme cascade is to terminate the action of the co-transmitter ATP, generating adenosine.

Na+ Modulates Anion Permeation and Block of P2X7 Receptors from Mouse Parotid Glands

“…We don’t know the reason for this discrepancy but acinar cells express both P2X 4 and P2X 7 receptors in an unknown ratio and this could contribute to changes in ATP sensitivity. In addition, a higher ecto-nucleotidase activity in acinar cells compared to HEK-293 cells could also contribute to change the apparent ATP sensitivity of endogenous channels (Henz et al, 2006). Control experiments show that HEK-293 cells transfected with either P2X 4 or an inverted sequence of P2X 7 did not exhibit the ATP-activated current (inset in Figure 4).…”

Influence of antidepressant drugs on Ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPPs) from salivary glands of rats

“…3 Extracellular hydrolysis of ATP to adenosine promoted by ectonucleotidases has been reported for several cell types, [32][33][34] including salivary glands. 14,15 Tricyclic antidepressants have shown common side effects, that can occur indirectly (central nervous system) and/or directly (salivary glands). 22,35 In this study, we observed an increase in enzyme activity when p-Nph-5 0 -TMP was used as substrate in rats submitted to IMI treatment.…”

“…13 These families of enzymes reveal not only overlapping tissue distributions, but also overlapping substrate specificities and functions. 1 Various types of enzymes mediate the saliva production and we have described in a previous study the presence of an E-NTPDase, an ecto-5 0 -nucleotidase 14 and an E-NPP 15 in acinar cells. NTPDase1 showed weak immunoreactivity whereas NTPDase2 activity was slightly higher in plasma membranes of nerve terminals and membranes of nerve fibres in salivary glands.…”

Rat submandibular glands secrete nanovesicles with NTPDase and 5′-nucleotidase activities

“…Salivary glands also express different NTPDase isoforms that contribute to regulate nucleotide concentration in these systems [12]. NTPDase1 was identified by immunohistochemistry in mucous acinar and ductal cells and also zymogen granules of mouse submandibular salivary gland [13].…”