1. A regulated apical Na(+) conductance in dexamethasone-treated H441 airway epithelial cells.
- Author
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Ramminger SJ, Richard K, Inglis SK, Land SC, Olver RE, and Wilson SM
- Subjects
- Cell Membrane metabolism, Cell Polarity physiology, Cells, Cultured, Colforsin pharmacology, Epithelial Sodium Channels, Humans, Membrane Potentials drug effects, RNA, Messenger analysis, Respiratory Mucosa cytology, Sodium metabolism, Sodium Channels genetics, Dexamethasone pharmacology, Glucocorticoids pharmacology, Respiratory Mucosa drug effects, Respiratory Mucosa metabolism, Sodium Channels metabolism
- Abstract
Treating H441 cells with dexamethasone raised the abundance of mRNA encoding the epithelial Na(+) channel alpha- and beta-subunits and increased transepithelial ion transport (measured as short-circuit current, I(sc)) from <4 microA.cm(-2) to 10-20 microA.cm(-2). This dexamethasone-stimulated ion transport was blocked by amiloride analogs with a rank order of potency of benzamil >or= amiloride > EIPA and can thus be attributed to active Na(+) absorption. Studies of apically permeabilized cells showed that this increased transport activity did not reflect a rise in Na(+) pump capacity, whereas studies of basolateral permeabilized cells demonstrated that dexamethasone increased apical Na(+) conductance (G(Na)) from a negligible value to 100-200 microS.cm(-2). Experiments that explored the ionic selectivity of this dexamethasone-induced conductance showed that it was equally permeable to Na(+) and Li(+) and that the permeability to these cations was approximately fourfold greater than to K(+). There was also a small permeability to N-methyl-d-glucammonium, a nominally impermeant cation. Forskolin, an agent that increases cellular cAMP content, caused an approximately 60% increase in I(sc), and measurements made after these cells had been basolaterally permeabilized demonstrated that this response was associated with a rise in G(Na). This cAMP-dependent control over G(Na) was disrupted by brefeldin A, an inhibitor of vesicular trafficking. Dexamethasone thus stimulates Na(+) transport in H441 cells by evoking expression of an amiloride-sensitive apical conductance that displays moderate ionic selectivity and is subject to acute control via a cAMP-dependent pathway.
- Published
- 2004
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