Coupling of CFTR-mediated anion secretion to nucleoside transporters and adenosine homeostasis in calu-3 cells

Abstract

The purpose of this study was to characterize the role of adenosine-dependent regulation of anion secretion in Calu-3 cells. RT-PCR studies showed that Calu-3 cells expressed mRNA for A2A and A2B but not A1 or A3 receptors, and for hENT1, hENT2 and hCNT3 but not hCNT1 or hCNT2 nucleoside transporters. Short-circuit current measurements indicated that A2B receptors were present in both apical and basolateral membranes, whereas A2A receptors were detected only in basolateral membranes. Uptake studies demonstrated that the majority of adenosine transport was mediated by hENT1, which was localized to both apical and basolateral membranes, with a smaller hENT2-mediated component in basolateral membranes. Whole-cell current measurements showed that application of extracellular nitrobenzylmercaptopurine ribonucleoside (NBMPR), a selective inhibitor of hENT1-mediated transport, had similar effects on whole-cell currents as the application of exogenous adenosine. Inhibitors of adenosine kinase and 5'-nucleotidase increased and decreased, respectively, whole-cell currents, whereas inhibition of adenosine deaminase had no effect. Single-channel studies showed that NBMPR and adenosine kinase inhibitors activated CFTR Cl- channels. These results suggested that the equilibrative nucleoside transporters (hENT1, hENT2) together with adenosine kinase and 5'-nucleotidase play a crucial role in the regulation of CFTR through an adenosine-dependent pathway in human airway epithelia.

A2B Adenosine Receptors Regulate the Mucus Clearance Component of the Lung's Innate Defense System

“…Pretreatment with caffeine attenuated this activation ( Figure 2). Caffeine is a nonspecific ADO-R antagonist and we cannot exclude the possibility that this activation was mediated by A 2A -R. However, A 2A -R is thought to be serosally located in the airway epithelia and may not have been activated during our nasal PD experiments (38). Caffeine can also act as a phosphodiesterase inhibitor, which could raise cAMP and confound our results.…”

Adenosine Promotes IL-6 Release in Airway Epithelia

“…Early studies suggested the presence of A2B and A2A but not A1 and A3 adenosine receptors in Calu-3 cells (11,42). ZM241385, an A2A receptor-selective blocker, attenuated adenosine-induced IL-6 release (Fig.…”

“…A2A and A2B adenosine-receptor subtypes have been found in Calu-3 cells (11,42). Previous studies suggest that both apical and basolateral A2B receptors are coupled with cystic fibrosis transmembrane conductance regulator (CFTR) activation and transepithelial anion secretion (8,11,42).…”

“…Previous studies suggest that both apical and basolateral A2B receptors are coupled with cystic fibrosis transmembrane conductance regulator (CFTR) activation and transepithelial anion secretion (8,11,42). However, the role of apical A2A adenosine receptors has not been described, although the basolateral A2A receptors appear to mediate transepithelial anion secretion (11).…”

“…Adenosine signaling regulates distinct Cl Ϫ channels, mucin secretion, and ciliary mobility (7)(8)(9)(10)(11) and is believed to play a key role in mucociliary clearance (8,9). Despite the rather rich information about its involvement in other physiological processes, little is known about the role of adenosine in the inflammatory responses of airway epithelial cells.…”