The binding of ethacrynic acid to rabbit kidney cortex

Abstract

1. 1. The uptake of labeled ethacrynic acid by slices of rabbit kidney cortex at 25 °C approached a steady state level by 1 h of incubation, was linearly dependent on the external concentration of the compound, and was not affected by metabolic inhibitors. 2. 2. The apparent steady state level of ethacrynic acid in the tissue considerably exceeded the external concentration. Evidence for binding of ethacrynic acid by tissue components was obtained as follows: (a) 40 % of the label could not be washed out; (b) the same fraction of the label was found in a well washed tissue solid sedimenting at up to 18 000 × g. 3. 3. The presence of the thiol reagents N-ethylmaleimide, HgCl 2, and iodoacetic acid did not diminish binding of ethacrynic acid. 4. 4. Neither the uptake into nor the efflux from rabbit kidney cortex of ethacrynic acid was modified by the presence, in various concentrations, of materials presumably associated with sites of active transport of ions and sugars, e.g. ouabain, normally actively transported sugar, and Na +. 5. 5. It was concluded that the major part of the binding of ethacrynic acid by rabbit kidney cortex was not specific for either tissue sulfhydryl groups nor unique membrane active transport sites.