Volume Regulation of Thick Ascending Limb of Henle Cells: Significance of Organic Osmolytes

Abstract

The thick ascending loop of Henle (TALH) is exposed to high osmotic stress, which is particularly due to high sodium and chloride reabsorption and very low water permeability of the luminal membrane. Therefore, the volume regulation of TALH cells, derived from the TALH loop of rabbit kidneys, was analyzed. The volume was determined by impedance measurements. TALH cells, which were adapted to different osmolarities (300 and 600 mosm/l), showed no significant differences in their cell volume. Therefore, a complete volume regulation could be supposed. An increase in extracellular osmolarity from 300 to 600 mosm/l (osmolarity adjusted by addition of 150 mM NaCl) immediately led to a reduction in the cell volume by 37 ± 6% (n = 6). A regulatory volume increase (RVI) was not observed within 10 min but after 24 h. Conversely, a sudden cell swelling by 44 ± 5% (n = 4) was detected within 20 s following an extracellular hypoosmotic challenge (from 600 to 300 mosm/l). The subsequent volume regulatory decrease (RVD) required a period of 7 days. Specific inhibitors of important ion transporters had no effect on volume regulation. Thus, changes in the ion conductivity do not seem to influence the processes of RVI and RVD. Conversely, the intracellular content of the organic osmolytes, sorbitol, inositol, betaine, and glycerophosphorylcholine, changed in the course of RVI and RVD. These results provide evidence that TALH cells are capable of maintaining their volume despite large extracellular osmotic changes. RVI and RVD are mainly regulated by changes in the intracellular content of organic osmolytes within 1 and 7 days.

Cellular distribution of NKCC2 in the gastric mucosa and its response to short-term osmotic shock

“…The increment of NKCC2 protein in TALH cells results in long-term potentiation of NaCl reabsorbtion (Kim et al 1999;Besseghir et al 1986;Riazi et al 2009). Nevertheless, contradictory results exist on its participation in cell-volume regulation of TALH (Grunewald et al 2001;Eveloff and Calamia 1986). In the present study, we have found that, in contrast to NKCC1, hypertonic stress causes a significant downregulation in NKCC2 protein level with no obvious membrane translocation.…”

“…As regards to NKCC2, its three splice variants, identified along the thick ascending limb of loop of Henle (TALH) in the mammalian kidney, are partially inhibited by hypotonicity but to different extents (Plata et al 2002). NKCC2 seems not to respond to hypotonic stress in the eel intestine (Lionetto et al 2005) nor to hypertonic stress in rabbit TALH cells (Grunewald et al 2001). Few studies have directly addressed the regulation of NKCC expression in response to osmotic shock.…”

Renal Cells Express Different Forms of Vimentin: The Independent Expression Alteration of these Forms is Important in Cell Resistance to Osmotic Stress and Apoptosis

“…As an important part in the urinary concentration mechanism, renal tubular cells are able to restore their cell volume to normal despite high changes in extracellular osmolarity [27]. However; their adaptive mechanism has remained poorly characterized, and the underlying signaling pathways are poorly explored.…”

Effects of 20-HETE on Na+transport and Na+-K+-ATPase activity in the thick ascending loop of Henle

“…However, a previous study concluded (8) that 20-HETE inhibits Na ϩ -K ϩ -2Cl Ϫ cotransporter directly, because it decreased rather than increased the Na ϩ content of rabbit mTALH cells. However, only the steady-state Na ϩ content of the cells was measured by flame photometry after extensive washing of the cells with Na ϩ -free medium, and interpretation of this type of measurement can be difficult, since mTALH volume is regulated by opening of nonselective cation channels and cells lose intracellular Na ϩ and K ϩ when exposed to osmotic gradients (15). More recently, Na ϩ -sensitive fluorescent probes have been developed that allow for the dynamic measurement of changes in [Na ϩ ] i in proximal tubules (30,39) and mTALH (19).…”