Abstract
The kidney medulla is exposed to very high interstitial osmolarity leading to the activation of mitogen-activated protein kinases (MAPK). However, the respective roles of increased intracellular osmolality and of cell shrinkage in MAPK activation are not known. Similarly, the participation of MAPK in the regulatory volume increase (RVI) following cell shrinkage remains to be investigated. In the rat medullary thick ascending limb of Henle (MTAL), extracellular hypertonicity produced by addition of NaCl or sucrose increased the phosphorylation level of extracellular signal-regulated kinase (ERK) and p38 kinase and to a lesser extent c-Jun NH(2)-terminal kinase with sucrose only. Both hypertonic solutions decreased the MTAL cellular volume in a dose- and time-dependent manner. In contrast, hypertonic urea had no effect. The extent of MAPK activation was correlated with the extent of MTAL cellular volume decrease. Increasing intracellular osmolality without modifying cellular volume did not activate MAPK, whereas cell shrinkage without variation in osmolality activated both ERK and p38. In the presence of 600 mosmol/liter NaCl, the maximal cell shrinkage was observed after 10 min at 37 degrees C and the MTAL cellular volume was reduced to 70% of its initial value. Then, RVI occurred and the cellular volume progressively recovered to reach about 90% of its initial value after 30 min. SB203580, a specific inhibitor of p38, almost completely inhibited the cellular volume recovery, whereas inhibition of ERK did not alter RVI. In conclusion, in rat MTAL: 1) cell shrinkage, but not intracellular hyperosmolality, triggers the activation of both ERK and p38 kinase in response to extracellular hypertonicity; and 2) RVI is dependent on p38 kinase activation.
Highlights
The kidney medulla is exposed to very high interstitial osmolarity leading to the activation of mitogen-activated protein kinases (MAPK)
Hypertonic NaCl and Sucrose but Not Urea Increased extracellular signal-regulated kinases and 2 (ERK) and p38 Kinase Phosphorylation in medullary thick ascending limb of Henle (MTAL) Cells—MTAL suspensions, as well as microdissected MTALs were incubated for 15 min at 37 °C in isotonic or hypertonic incubation solution
The present study shows that cell shrinkage induced by extracellular hypertonicity activates Mitogen-activated protein (MAP) kinases in rat MTAL
Summary
The mechanisms of their activation by extracellular hypertonicity need to be clarified. Neither the respective role of intracellular hypertonicity versus cell shrinkage in the activation of MAP kinases by extracellular hyperosmolality nor the relationship between the MAP kinase activation and the regulatory cell volume increase have been investigated. We have undertaken this study: 1) to examine the effects of different solutes on the activation of MAP kinases in MTAL cells by hypertonicity, and 2) to analyze the relationship between MAP kinase activation and cell volume variations
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