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Characteristics of ionic binding by rat renal tissue in vitro.

A study has been made of Na+ and Cl‐ binding in metabolically inhibited slices of rat renal cortex and outer medulla incubated in modified Krebs phosphate‐bicarbonate Ringer solution. At pH 7.35 in control media (cortex, 147 mmol Na+/l, 105 mmol Cl‐/l; outer medulla, 187 mmol Na+/l, 145 mmol Cl‐/l) cortical slices bound (mean) 171 nmol Na+ and 56.7 nmol Cl‐/mg solute‐free dry weight; outer medullary slices bound 188 nmol Na+/mg and negligible amounts of Cl‐. In both regions, Na+ was exchangeable on a 1:1 basis for K+ or Li+ in media containing equal concentrations of each cation: Na+ was completely displaced by La3+. In cortical slices in media containing equimolar Cl‐ and other monovalent anions, binding occurred according to the sequence acetate less than or equal to salicylate less than or equal to Cl‐ less than SCN‐; Cl‐ was completely displaced by PO4(3‐). When medium pH was lowered, Na+ binding was markedly reduced in both regions, whereas Cl‐ binding increased (and became significant in outer medulla). In NaCl solutions, Na+ binding capacity was saturated at control Na+ concentrations. When [Na+] was progressively reduced (iso‐osmolality being maintained by addition of urea), bound Na+ in both regions was nearly linearly related to log medium [Na+]. Raising medium osmolality with urea caused decreased Na+ binding and increased Cl‐ binding in both regions. Na+ binding in both regions was significantly reduced by pre‐treatment with chondroitinase ABC. Binding of both ions was independent of temperature within the range 2‐37 degrees C. The possibility is raised that renal ionic binding might influence vectorial ion transport by affecting free ion activity in the region of the transporting cells.