Permselectivity for cations over anions in the upper portion of descending limbs of Henle's loop of long-loop nephron isolated from hamsters.

The permselectivity of the upper portion of long descending limb of Henle (LDLu) was investigated with electrophysiological methods in the isolated perfused tubule preparation of hamster kidney. The diffusion potential (Vt) was determined in three different protocols. In protocol 1, the tubules were initially perfused with modified Krebs Ringer's solution on both sides of the epithelium. Then the bath solution was exchanged consecutively with another solution in which 50 mmol/l NaCl replaced by 50 mmol/l KCl, RbCl, NH4Cl, CsCl, LiCl, NaBr, NaNO3, NaI, Na acetate or 75 mmol/l NaCl replaced by mannitol. The permeabilities for these ions relative to chloride were calculated by Goldman's constant field equation. The segment was found to be cation selective, with all cations being 5-9 times more permeable than all anions. The sequence of permeability was K+ greater than Rb+ greater than Li+ greater than NH+4 = Cs+ greater than or equal to Na+ much greater than Cl- greater than or equal to Br- greater than or equal to NO3- greater than or equal to I- greater than Acetate-. In protocol 2, pure 150 mM NaCl was used for the basal solution to avoid interference by other ions. The bathing solution was exchanged by other solutions which contained 150 mmol/l KCl, NH4Cl, CsCl, RbCl, LiCl, NaI, NaBr, NaNO3, Na acetate or 75 mmol/l NaCl with mannitol. Thus simple biionic substitution was performed. Again, the segment was found to be cation selective, with all cations being 4-10 times more permeable than all anions.(ABSTRACT TRUNCATED AT 250 WORDS)