5 research outputs found
Sildenafil Acts as Potentiator and Corrector of CFTR but Might be not Suitable for the Treatment of CF Lung Disease
Expression of ENaC and other Transport Proteins in Xenopus Oocytes is Modulated by Intracellular Na+
The expression of the epithelial Na+ channel (ENaC) is tissue-specific and dependent on a variety of mediators and interacting proteins. Here we examined the role of intracellular Na+ ([Na+](i)) as a modulator of the expression of rat ENaC in Xenopus laevis oocytes. We manipulated [Na+](i) of ENaC-expressing oocytes in the range of 0-20 mM by incubating in extracellular solutions of different [Na+](o). Electrophysiological, protein biochemical and fluorescence optical methods were used to determine the effects of different [Na+]i on ENaC expression and membrane abundance. In voltage-clamp experiments we found that amiloride-sensitive ENaC current (Iami) and conductance (Gami) peak at a [Na+](i) of approximately 10 mM Na+, but were significantly reduced in 5 mM and 20 mM [Na+](i). Fluorescence intensity of EGFP-ENaC-expressing oocytes also followed a bell-shaped curve with a maximum at approximately 10 mM [Na+](i). In Western blot experiments with specific anti-ENaC antibodies the highest protein expression was found in ENaC-expressing oocytes with [Na+](i) of 10-15 mM. Since ENaC is also highly permeable for Li+, we incubated ENaC-expressing oocytes in different Li+ concentrations and found a peak of Iami and Gami with 5 mM Li+. The influence of [Na+](i) on the expression is not ENaC-specific, since expression of a Cl(-) channel (CFTR) and a Na+/glucose cotransporter (SGLT1) showed the same dependence on [Na+](i). We conclude that specific concentrations of Na+ and Li+ influence the expression and abundance of ENaC and other transport proteins in the plasma membrane in Xenopus laevis oocytes. Furthermore, we suggest the existence of a general mechanism dependent on monovalent cations that optimizes the expression of membrane proteins.status: publishe