Effects of inhibitors of Na and Cl transport on oxygen consumption in the bullfrog cornea

Abstract

The oxygen consumption of isolated bullfrog corneas in NaCl, Na 2SO 4 (Cl-free) and choline Cl (Na-free) Ringer's solution was studied, and also the effects on oxygen consumption of the inhibitors of Cl transport: furosemide, ethacrynic and dihydroethacrynic acids. The removal of Cl from the bathing medium inhibited oxygen consumption by 19% while its addition to a Cl-free medium stimulated oxygen consumption by 14%. Na removal from the bathing medium inhibited oxygen consumption by 36%. Furosemide inhibited oxygen consumption (16%) only in NaCl Ringer's solution. Ethacrynic and dihydroethacrynic acids inhibited oxygen consumption in NaCl and Cl-free media but their effects were less specific. The inhibitors of Na and Cl transport: ouabain and tryptamine, inhibited oxygen consumption in NaCl Ringer's solution by 34 and 26%, respectively. In Cl-free Ringer's solution, ouabain and tryptamine inhibited oxygen consumption by 18 and 14%, respectively. These results are pertinent for characterizing the coupling between aerobic metabolism and transepithelial active transport of Na and Cl. The fractions of suprabasal oxygen consumption supporting Na and Cl transport are found to be nearly equal while the rate of net transepithelial Cl transport is known to be at least four times as large as the rate of net active Na transport. Based on the furosemide effect on oxygen consumption and the electrical energy dissipation through the active Cl transport pathway, an energy efficiency utilization by Cl transport of about 50% is calculated.