Fate of ATP in secretory granules: Phosphohydrolase studies in pancreatic vascular bed.

Abstract

Mature secretory granules in paraneurons contain ATP amongst other small messenger molecules. In the islet organ such stores of adenine nucleotides readily can be demonstrated by means of the quinacrine fluorescence method. ATP is co-released together with other granule constituents when the major hormones are exocytosed. The distribution of ATP splitting enzymic activities was studied in the pancreas of the mouse and rat, in order to obtain information on the possible fate of this small messenger molecule. ATPase, ADPase, and AMPase (5'-nucleotidase) were demonstrated with lead precipitation methods, L-tetramisole was used to inhibit unspecific alkaline phosphatase (alPase); alPase activities were shown with tetrazolium methods, using 5-bromo-4-chloro-3-indoxyl phosphate as substrate. Most endothelial cells of the vascular bed, both in the exocrine and in the endocrine pancreas, are reactive for ATPase, ADPase, AMPase and alPase. Smooth muscle cells are strongly reactive for ATPase and AMPase, vascular adventitial fibroblasts (veil cells) stain for ATPase and alPase, as do some lamellar cells at the islets surface. Staining for ADPase serves as a selective method to demonstrate the vascular bed. Comparable results are obtained with the alPase reaction, though insular non-B-cells are also reactive. ATPase staining is less useful for demonstrating vascular connections because moderate reactivity of exocrine parenchyma and adventitial tissue obscures the picture. AMPase activity is strong in the venous segments of the capillary net and in collecting veins but the reaction obviously does not demonstrate significant portions of the residual capillary network. Weak AMPase activity is seen in the insular parenchyma.(ABSTRACT TRUNCATED AT 250 WORDS)