Regulation of the Na+/Ca2+ Exchanger in Rat Pancreatic Ducts

Abstract

The Ca2+ content of pancreatic juice is closely regulated by yet unknown mechanisms. One aim of the present study was to find whether rat pancreatic ducts have a Na+/Ca2+ exchanger, as found in some Ca2+ transporting epithelia. Another aim was to establish whether the exchanger is regulated by hormones/agonists affecting pancreatic secretion. Whole pancreas, pure pancreatic acini and ducts were obtained from rats and used for RT-PCR and Western blot analysis, immunohistochemistry and intracellular Ca2+ measurements using Fura-2. RT-PCR analysis indicated Na+/Ca2+-exchanger isoforms NCX1.3 and NCX1.7 in acini and pancreas. Western blot with NCX1 antibody identified bands of 70, 120 and 150 kDa in isolated ducts, acini and pancreas. Immunofluorescence experiments showed the Na+/Ca2+ exchanger on the basolateral membrane of acini and small intercalated/intralobular ducts, but in larger intralobular/extralobular ducts the exchanger was predominantly on the luminal membrane. Na+/Ca2+ exchange in ducts was monitored by changes in intracellular Ca2+ activity upon reversal of the Na+ gradient. Secretin (1 nM) and carbachol (1 mM) reduced Na+/Ca2+ exchange by 40% and 51%, respectively. Insulin (1 nM) increased Na+/Ca2+ exchange by 230% within 5 min. The present study shows that pancreatic ducts express the Na+/Ca2+ exchanger. Its distinct localization along the ductal tree and regulation by secretin, carbachol and insulin indicate that ducts might be involved in regulation of Ca2+ concentrations in pancreatic juice.

Differential Regulation of the Apical Plasma Membrane Ca2+-ATPase by Protein Kinase A in Parotid Acinar Cells

“…NCX is also a low affinity, high capacity [Ca 2ϩ ] i clearance pathway driven by the electrochemical Na ϩ gradient and thus has a dominant role in electrically excitable cells such as cardiac myocytes (21). To the authors' knowledge, there is no evidence that parotid acinar cells express NCX; however, in the related pancreatic duct cells, NCX has been shown to contribute to [Ca 2ϩ ] i clearance and to be localized to the apical membrane (22). It is therefore conceivable that a similar mechanism exists in Par-C10 cells, because of de-differentiation to a more ductal-like origin.…”

Purinergic Receptors Stimulate Na⁺/Ca^2+ Exchange in Pancreatic Duct Cells: Possible Role of Proteins Handling and Transporting Ca^2+

“…Intercalated and small intralobular ducts were obtained by collagenase digestion method; these were too small and fragile for perfusion, compared to ducts used for perfusion in our other studies [7,19]. Ducts were held by holding pipettes and both luminal and basolateral sides were accessible to bath solutions.…”

“…In addition, NCX may not only be important in regulating intracellular Ca 2+ signalling, but at the organ level it could be a part of transepithelial Ca -ATPase (PMCA) and calcium sensing receptors (CaR) [8][9][10][11]. In pancreas, the normal pancreatic juice contains relatively low Ca 2+ concentrations (<0.5 mM) [12][13][14], but except for a few studies on CaR [15,16] and our studies on NCX [6,7] transport. Present study was performed on rat pancreatic ducts and on cells from human pancreatic duct lines CFPAC-1 (also PANC-1 and Capan-1), which are commonly used as models for epithelial transport of human pancreatic ducts [2].…”

“…However, Ca 2+ signals were inhibited at high nucleotide concentrations, possibly due to unusual stimulation of Ca 2+ efflux. Since rat pancreatic ducts express Na + /Ca 2+ exchanger (NCX1), which is regulated 388 by secretin, acetylcholine and insulin [6,7], it was worth considering whether P2 receptors could regulate this exchanger on a single cell level. In addition, NCX may not only be important in regulating intracellular Ca 2+ signalling, but at the organ level it could be a part of transepithelial Ca -ATPase (PMCA) and calcium sensing receptors (CaR) [8][9][10][11].…”

Molecular mechanisms underlying Ca2+-mediated motility of human pancreatic duct cells

“…Two subfamilies have been described in mammalian cells: one in which Ca 2ϩ movement is dependent only on Na ϩ (NCX1-3) and the other in which Ca 2ϩ transport is also dependent on K ϩ (NCKX1-6). TRPC and NCX have been described in mammalian tissues for decades, but very little is known about the expression and function of these proteins in human pancreatic cancer cells (4,22,32). Although the role of TRP channels has been reported in colorectal, colon, thyroid, breast, ovarian, and prostate cancer (7,64), the involvement of TRP channels and NCX in pancreatic cancer development is currently unexplored.…”