Item

Abstract

Active transport potentials were studied across early loops of rat proximal tubule during luminal perfusion and peritubular superfusion with HCO₃-Ringer's solution of identical ionic composition. From the effects of the carbonic anhydrase inhibitor acetazolamide and of ouabain it is concluded 1. that the lumenpositive active transport potential indicates an excess of active H⁺ secretion/HCO₃⁻ absorption over active Na⁺ absorption and 2. that the lumen-negative active transport potential, which develops in the presence of glucose (and/or aminoacids) in the tubular lumen, indicates stimulation of active Na⁺ absorption. Ouabain did not abolish the lumen-positive potential difference suggesting that active H⁺/HCO₃⁻ transport and active Na⁺ transport may be to some extent independent. Among the diuretics tested the mercurial diuretic mersalyl acted primarily on Na⁺ transport, and furosemide acted on HCO₃⁻ transport, whereas the effect of ethacrynic acid appeared to be unspecific.