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

Abstract

Extracellular nucleotides modulate a wide number of biological processes such as neurotransmission, platelet aggregation, muscle contraction, and epithelial secretion acting by the purinergic pathway. Nucleotidases as NTPDases and ecto-5′-nucleotidase are membraneanchored proteins that regulate extracellular nucleotide concentrations. In a previous work, we have partially characterized an NTPDase-like activity expressed by rat submandibular gland microsomes, giving rise to the hypothesis that membrane NTPDases could be released into salivary ducts to regulate luminal nucleotide concentrations as was previously proposed for ovarian, prostatic, and pancreatic secretions. Present results show that rat submandibular glands incubated in vitro release membrane-associated NTPDase and ecto-5′-nucleotidase activities. Electron microscopy images show that released membranes presenting nucleotidase activity correspond to exosome-like vesicles which are also present at microsomal fraction. Both exosome release and nucleotidase activities are raised by adrenergic stimulation. Nucleotidase activities present the same kinetic characteristics than microsomal nucleotidase activity, corresponding mainly to the action of NTPDase2 and NTPDase3 isoforms as well as 5′-nucleotidase. This is consistent with Western blot analysis revealing the presence of these enzymes in the microsomal fraction.

ATP release, generation and hydrolysis in exocrine pancreatic duct cells

“…We also found NTPDase2 protein in Capan-1 cells, as well as secreted extracellular enzyme detected in a particulate fraction, which suggests microvesicular secretion. Such microvesicular secretion of ecto-nucleotidases has been proposed also for the rat pancreas and submandibular glands [14,73]. Overall, it appears that pancreatic ducts express ectoenzymes somewhat different to acini and to pancreatic juice arising from stimulation of acinar by cholecystokinin.…”

Purinergic Signaling in Oral Tissues

“…It was previously demonstrated that e-5′NT and NTPDase1, 2 and 3, but not NTPDase8, are expressed in rat SMG, mostly associated to microsomes [ 78 ]. Subsequently, this activity was predominantly attributed to substrate inactivation by rat and human NTPDase2 [ 79 ]. Furthermore, it has been reported that nanovesicles contained in rat saliva have the ability to hydrolyze ATP.…”