title: Effect of osmolarity on cation fluxes in medullary thick ascending limb cells.
abstract: The effects of a hypertonic extracellular medium on furosemide-sensitive Na and K fluxes were studied in isolated cells from the rabbit medullary thick ascending limb of Henle's loop (mTALH). In the control incubation medium, the furosemide-sensitive 22Na uptake was 379.1 +/- 24.4 pmol . mg protein-1 . min-1 and the furosemide-sensitive 86Rb uptake was 30.5 +/- 16.9. The furosemide-sensitive 22Na flux was not stimulated by K gradients directed into the cells, and, conversely, the furosemide-sensitive 86Rb flux was not stimulated by Na gradients directed into the cells. These findings are consistent with a Na-Cl cotransport system. In the presence of 200 mM mannitol, the furosemide-sensitive 22Na and 86Rb fluxes were increased dramatically to 919.4 +/- 76.6 and 106.1 +/- 29.2 pmol . mg protein-1 . min-1, respectively. When the osmolarity of the incubation medium was increased, not only were the furosemide-sensitive fluxes increased but these fluxes became inter-dependent, i.e., removing Na or K prevented the increase in the furosemide-sensitive flux of the other cation. This finding is consistent with a Na-K-2Cl cotransport system in the mTALH cells. The data suggest that the Na-Cl and the Na-K-2Cl cotransport systems may be distinct functions of the same furosemide-sensitive cotransport system and that their expression may be regulated by changes in cell volume.
mesh_terms: D000818:Animals; D002469:Cell Separation; D005665:Furosemide / Q000494:pharmacology; D007679:Kidney Medulla; D007684:Kidney Tubules / Q000378:metabolism*; D008138:Loop of Henle / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D011868:Radioisotopes; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
chemical_list: D011868:Radioisotopes; D005665:Furosemide; D012964:Sodium; D012413:Rubidium; D011188:Potassium