Developmental regulation of the concentrative nucleoside transporters CNT1 and CNT2 in rat liver

“…It is not clear whether the differences of transport activities and expression profiles of nucleoside transporters between primarycultured rat Sertoli cells and TM4 cells are due to species difference or differences in the age of animals and/or cell culture conditions. In the rat liver, the expression pattern of nucleoside transporters is developmentally regulated (del Santo et al, 2001). Adult rat hepatocytes show Na ϩ -dependent uridine uptake, whereas fetal hepatocytes exhibit NBMPR-sensitive equilibrative Na ϩ -independent transport.…”

Section: Discussionmentioning

confidence: 99%

Nucleoside Transport at the Blood-Testis Barrier Studied with Primary-Cultured Sertoli Cells

Kato

Maeda

Akaike

et al. 2004

J Pharmacol Exp Ther

View full text Add to dashboard Cite

Nucleosides are essential for nucleotide synthesis in testicular spermatogenesis. In the present study, the mechanism of the supply of nucleosides to the testicular system across the blood-testis barrier was studied using primary-cultured Sertoli cells from rats and TM4 cells from mice. Uptake of uridine by these cells was time-and concentration-dependent. Uridine uptake was decreased under Na ϩ -free conditions, and the system was presumed to be high affinity, indicating an Na ϩ -dependent concentrative nucleoside transporter (CNT) is involved. On the other hand, nitrobenzylthioinosine, a potent inhibitor of Na ϩ -independent equilibrative nucleoside transporters (ENTs), inhibited uridine uptake by the Sertoli cells in a concentration-dependent manner. Expression of nucleoside transporters ENT1, ENT2, ENT3, CNT1, CNT2, and CNT3 was detected in Sertoli cells by reverse transcriptase-polymerase chain reaction analysis. Inhibition studies of the uptake of uridine by various nucleosides both in the presence and absence of Na ϩ indicated that the most of those expressed nucleoside transporters, ENTs and CNTs, are involved functionally. These results demonstrated that Sertoli cells are equipped with multiple nucleoside transport systems, including ENT1, ENT2, and CNTs, to provide nucleosides for spermatogenesis.

show abstract

“…Liver homogenates, basolateral plasma membranes isolated as previously described (14), and crude extracts from FAO cells were used. Samples were treated with 0.5% Triton X-100-10 mM Tris (pH 7.4), and 20-g protein aliquots were run on sodium dodecyl sulfate-10% polyacrylamide gels (10,13). Proteins were transferred to filters (Immobilon-P; 0.45-m-pore size; Millipore, Bedford, Mass.…”

Section: Methodsmentioning

confidence: 99%

ATP-Sensitive K⁺ Channels Regulate the Concentrative Adenosine Transporter CNT2 following Activation by A₁ Adenosine Receptors

Duflot

Riera

Fernández‐Veledo

et al. 2004

Molecular and Cellular Biology

View full text Add to dashboard Cite

This study describes a novel mechanism of regulation of the high-affinity Na ؉ -dependent adenosine transporter (CNT2) via the activation of A 1 adenosine receptors (A 1 R). This regulation is mediated by the activation of ATP-sensitive K ؉ (K ATP ) channels. The high-affinity Na ؉ -dependent adenosine transporter CNT2 and A 1 R are coexpressed in the basolateral domain of the rat hepatocyte plasma membrane and are colocalized in the rat hepatoma cell line FAO. The transient increase in CNT2-mediated transport activity triggered by (؊)-N 6 -(2-phenylisopropyl)adenosine is fully inhibited by K ATP channel blockers and mimicked by a K ATP channel opener. A 1 R agonist activation of CNT2 occurs in both hepatocytes and FAO cells, which express Kir6.1, Kir6.2, SUR1, SUR2A, and SUR2B mRNA channel subunits. With the available antibodies against Kir6.X, SUR2A, and SUR2B, it is shown that all of these proteins colocalize with CNT2 and A 1 R in defined plasma membrane domains of FAO cells. The extent of the purinergic modulation of CNT2 is affected by the glucose concentration, a finding which indicates that glycemia and glucose metabolism may affect this cross-regulation among A 1 R, CNT2, and K ATP channels. These results also suggest that the activation of K ATP channels under metabolic stress can be mediated by the activation of A 1 R. Cell protection under these circumstances may be achieved by potentiation of the uptake of adenosine and its further metabolization to ATP. Mediation of purinergic responses and a connection between the intracellular energy status and the need for an exogenous adenosine supply are novel roles for K ATP channels.Adenosine is an autocoid that acts physiologically on specific cell surface G protein-coupled receptors, four of which (A 1 , A 2A , A 2B , and A 3 ) have been cloned and described pharmacologically (18,23,39). A 1 adenosine receptors (A 1 R) mediate a broad range of signaling responses by coupling to Gi and Go proteins (18,23,33). The activation of A 1 R regulates several membrane and intracellular proteins, such as adenylate cyclase, phospholipase C, Ca 2ϩ channels (23, 39), and K ϩ channels (3,26,35). mRNAs encoding the four adenosine receptors have been detected in liver cells (12). In isolated rat hepatocytes, the activation of A 1 R triggered Ca 2ϩ -mediated glycogenolysis, the activation of A 2 adenosine receptors stimulated cyclic AMP (cAMP)-mediated gluconeogenesis, and the activation of A 3 adenosine receptors increased cytosolic Ca 2ϩ and decreased cAMP levels, with minor changes in glycogen metabolism (20). In hepatocyte plasma membranes, the stimulation of adenylate cyclase activity and the inhibition of low-K m cAMP phosphodiesterase activity are coordinately regulated by glucagon, and A 1 R can inhibit glucagon-stimulated cAMP accumulation by blocking the effect of glucagon on phosphodiesterase activity (40). Moreover, a signal pathway involving A 2a adenosine receptors, Gi proteins, phospholipase C, protein kinase C (PKC) ␦, PKC ε, and p38 mitogen-activated prote...

show abstract

Developmental regulation of the concentrative nucleoside transporters CNT1 and CNT2 in rat liver

Cited by 37 publications

References 29 publications

Xenobiotic, Bile Acid, and Cholesterol Transporters: Function and Regulation

Xenobiotic, Bile Acid, and Cholesterol Transporters: Function and Regulation

Nucleoside Transport at the Blood-Testis Barrier Studied with Primary-Cultured Sertoli Cells

ATP-Sensitive K⁺ Channels Regulate the Concentrative Adenosine Transporter CNT2 following Activation by A₁ Adenosine Receptors

Contact Info

Product

Resources

About

Developmental regulation of the concentrative nucleoside transporters CNT1 and CNT2 in rat liver

Cited by 37 publications

References 29 publications

Xenobiotic, Bile Acid, and Cholesterol Transporters: Function and Regulation

Xenobiotic, Bile Acid, and Cholesterol Transporters: Function and Regulation

Nucleoside Transport at the Blood-Testis Barrier Studied with Primary-Cultured Sertoli Cells

ATP-Sensitive K+ Channels Regulate the Concentrative Adenosine Transporter CNT2 following Activation by A1 Adenosine Receptors

Contact Info

Product

Resources

About

ATP-Sensitive K⁺ Channels Regulate the Concentrative Adenosine Transporter CNT2 following Activation by A₁ Adenosine Receptors