Volume regulation in cortical collecting duct cells: role of AQP2

FORD, PAULA; RIVAROLA, VALERIA; CHARA, OSVALDO; BLOT-CHABAUD, MARCEL; CLUZEAUD, FRANÇOISE; FARMAN, NICOLETTE; PARISI, MARIO; CAPURRO, CLAUDIA

BIOLOGY OF THE CELL

Portland Press

Lugar: Londres; Año: 2005 vol. 97 p. 687 - 697

0248-4900

Background Information: The renal cortical collecting duct is involved in final urine volume and concentration via a process that is regulated by the antidiuretic-hormone arginine-vasopressin. This hormone induces an increase in water permeability due to translocation of Aquaporin-2 from intracellular vesicles to the apical membrane of principal cells. During transition from antidiuresis to diuresis, cortical collecting cells are exposed to changes in environment osmolality and cell volume regulation may be especially important for maintenance of intracellular homeostasis. Despite its importance, cell volume regulation in cortical collecting duct cells has been yet little investigated. Moreover, no studies have been carried out until today in order to evaluate the putative role of Aquaporins during this process in renal cells. Results: We have here studied regulatory volume responses after hypotonic or hypertonic challenges in two cortical collecting duct cell lines: one not expressing Aquaporins and other stably transfected with Aquaporin-2. We have used a fluorescent probe technique in which the acquisition of single-cell kinetic data can be simultaneously recorded with the intracellular pH. Experiments with hypertonic mannitol media demonstrated that, independently of Aquaporin-2 expression, cortical collecting duct cells shrink but fail to show regulatory volume increase, at least in the studied conditions. In contrast, under hypotonic shocks, regulatory volume decrease occurs and the activation of these mechanisms is more rapid in Aquaporin-2 transfected cells. This regulatory response takes place in parallel with intracellular acidification, which is faster in cells expressing Aquaporin-2. The acidification and the initial regulatory volume decrease response were inhibited by glibenclamide and barium chloride only in Aquaporin-2 cells. Conclusions: These results suggest that increases in the osmotic water permeability due to the expression of Aquaporin-2, are critical for a rapid activation of regulatory volume decrease mechanisms, which would be linked to cystic fibrosis transmembrane conductance regulator and to barium-sensitive potassium channels.