Cellular swelling in slices of rat renal outer medulla incubated in the presence of bovine serum albumin.

1. Cells in slices of rat renal outer medulla incubated for up to 100 min in modified phosphate-bicarbonate Ringer undergo reversible, concentration-dependent swelling (increase in water content) in the presence of bovine serum albumin (b.s.a). 2. Swelling also takes place in the presence of dextran sulphate, but neutral dextran or polyvinylpyrrolidone are without effect. 3. Swelling due to b.s.a. is pH-dependent, decreasing (relative to cell volume in the absence of b.s.a.) as pH is reduced. 4. Swelling due to b.s.a. is associated with the net cellular gain of Na+, the magnitude of which increases at pH is raised. 5. There is an accompanying pH-independent net loss of cellular K+; at pH greater than about 6.20 this loss is smaller than the uptake of Na+, and cells thus show net gain of monovalent cation. 6. The relationships between pH and percentage increase in cell water content and between pH and percentage increase in cell osmotic content due to net gain of cation in the presence of 8% b.s.a. are coincident within the range pH 6.15--7.60. 7. Studies on the volume of distribution of [125I]b.s.a. within slices suggests that more may bind to cells at low pH than at high pH.