Relationship between cell volume and cation content in thick ascending limb of rat kidney

We examined the relationship between the cell volume and cation concentration ([Nai] and [Ki]) of isolated segments of rat medullary thick ascending limb (MAL) after incubation at 30 degrees C in various isotonic solutions. When the tubules were incubated in a normal NaCl solution containing 5 mmol/l K+, addition of 1 mmol/l of ouabain increased [Nai] and decreased [Ki] but did not change the total ([Nai] + [Ki]) concentration (about 90 mEq/l) or tubular volume. After incubation in various K+-free solutions, the tubules were almost fully K+-depleted; their volume per unit of length was similar in the three solutions, although the choline Cl-treated tubules had a very low sodium content compared to the NaCl- and Na2SO4-treated tubules (8 vs. 97 and 95 mEq/l respectively). Ouabain altered neither volume nor [Nai] of tubules incubated in choline Cl or Na2SO4 solution. Transfer of tubules from K+-free Na2SO4 or K+-free choline Cl solution into K+-free NaCl solution resulted in an increase in [Nai] (by 29 and 97 mEq/l respectively) without much increase in tubular volume. A marked swelling of the tubules was only observed when the K+-free NaCl solution contained also ouabain. Under this condition, [Nai] was comparable to the Na+ concentration of the incubation medium. After washing and incubation in a normal NaCl solution containing K+, the swollen tubules recovered their initial volume and restored Na+ and K+ concentration gradients across the cell membranes.(ABSTRACT TRUNCATED AT 250 WORDS)