Rat pancreas secretes particulate ecto-nucleotidase CD39

Abstract

In exocrine pancreas, acini release ATP and the excurrent ducts express several types of purinergic P2 receptors. Thereby, ATP, or its hydrolytic products, might play a role as a paracrine regulator between acini and ducts. The aim of the present study was to elucidate whether this acinar-ductal signalling is regulated by nucleotidase(s), and to characterize and localize one of the nucleotidases within the rat pancreas. Using RT-PCR and Western blotting we show that pancreas expresses the full length ecto-nucleoside triphosphate diphosphohydrolase, CD39. Immunofluorescence shows CD39 localization on basolateral membranes of acini and intracellularly. In small intercalated/ interlobular ducts, CD39 immunofluorescence was localized on the luminal membranes, while in larger ducts it was localized on the basolateral membranes. Upon stimulation with cholecystokininoctapeptide-8 (CCK-8), acinar CD39 relocalizes in clusters towards the lumen and is secreted. As a result, pancreatic juice collected from intact pancreas stimulated with CCK-8 contained nucleotidase activity, including that of CD39, and no detectable amounts of ATP. Anti-CD39 antibodies detected the full length (78 kDa) CD39 in pancreatic juice. This CD39 was confined only to the particulate and not to the soluble fraction of CCK-8-stimulated secretion. No CD39 activity was detected in secretion stimulated by secretin. The role of secreted particulate, possibly microsomal, CD39 would be to regulate intraluminal ATP concentrations within the ductal tree. In conclusion, we show a novel inducible release of full length particulate CD39, and propose its role in the physiological context of pancreatic secretion.

Upregulation of CD39/NTPDases and P2 receptors in human pancreatic disease

“…Interestingly, acinar cells do not express P2X 7 receptors, whereas pancreatic ductal cells do (24,28). In general, pancreatic ducts show little desensitization of purinergic receptors, but only very few pancreatic acini show functional P2Rs (24,28).…”

“…By electron microscopy, granules in mouse pancreatic acini are shown to express CD39 and CD39L1. Additionally, Sorensen et al (28) have described ATP as a potential paracrine regulator between acini and ducts. Furthermore, CD39 can be released with a suitable stimulus into the lumen (28).…”

“…Additionally, Sorensen et al (28) have described ATP as a potential paracrine regulator between acini and ducts. Furthermore, CD39 can be released with a suitable stimulus into the lumen (28). Differences in CD39 localization and distribution of P2 and adenosine receptors might be responsible for functional alterations in the acinar-ductal system of injured rat pancreas.…”

“…The ATP release from acini may initiate its action downstream of the acini level in ductules and larger pancreatic ducts (28).…”

Ectonucleotidases in the digestive system: focus on NTPDase3 localization

“…Similarly, NTPDase3 and -2 may be involved in the modulation of P2X7 receptor activation on serous acinar cells. NTPDase1 expressed by pancreatic acini is released within the pancreatic juice (45). This may also occur in salivary glands as saliva, and pancreatic secretions are similar processes.…”