Hyposmolality-induced enhancement of ADH action on amiloride-sensitive Isc in renal epithelial A6 cells.
To assess the action of antidiuretic hormone (ADH) and the osmolality of bathing solution on amiloride-sensitive Na+ transport, we measured the amiloride-sensitive short-circuit current (Isc) and single-channel currents in renal epithelial A6 cells. The A6 cells were cultured on permeable supports for 9-13 d without aldosterone treatment. The basal amiloride-sensitive Isc and the density of the amiloride-sensitive Na+ channel at the apical membrane increased as the osmolality of the bathing solution decreased. ADH stimulated the amiloride-sensitive Isc. The stimulatory action of ADH was enhanced by low osmolality. The stimulatory action of hyposmolality on the amiloride-sensitive Isc was significantly diminished by pretreatment with brefeldin A (BFA, a blocker of protein translocation), while BFA had no significant effect on the ratio of ADH-stimulated amiloride-sensitive Isc to basal amiloride-sensitive Isc. These results suggest that hyposmolality stimulates the translocation of amiloride-sensitive Na+ channels to the apical membrane from the cytosolic store sites of the channel, and that ADH may activate amiloride-sensitive Na+ channels pre-existing in the apical membrane or translocate the channel via BFA-insensitive pathways in a manner dependent on the osmolality of the bathing solution in aldosterone-untreated A6 cells, differently from aldosterone-treated A6 cells in which ADH stimulates the translocation of amiloride-sensitive Na+ channels via BFA-sensitive pathways.
Niisato
N
N
Laboratory for Cellular and Molecular Physiology, Hospital for Sick Children Research Institute, University of Toronto, Ontario, Canada.
Marunaka
Y
Y
D000584:Amiloride / Q000494:pharmacology*; D020126:Brefeldin A; D002460:Cell Line; D003517:Cyclopentanes / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology*; D004553:Electric Conductivity; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D007038:Hypotonic Solutions / Q000494:pharmacology; D007668:Kidney / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D009994:Osmolar Concentration; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012076:Renal Agents / Q000494:pharmacology*; D014667:Vasopressins / Q000494:pharmacology*
D003517:Cyclopentanes; D004232:Diuretics; D007038:Hypotonic Solutions; D011500:Protein Synthesis Inhibitors; D012076:Renal Agents; D014667:Vasopressins; D020126:Brefeldin A; D000584:Amiloride