Sodium-chloride transport in the thick ascending limb of Henle's loop

Abstract

Isolated cells were prepared from the medullary thick ascending limb of Henle's loop (TALH) and the response of oxygen consumption was correlated with the active chloride transport system found in these cells. Oxygen consumption was 31.6 μl O₂/mg protein·h and inhibited 50% by the absence of either sodium or chloride in the incubation medium. The absence of both sodium and chloride produced no further inhibition of oxygen consumption. Ouabain (10⁻⁴ M) inhibited oxygen consumption by 50% and the inhibitory effect depended on the presence of both sodium and chloride in the incubation medium. Further, furosemide inhibited oxygen consumption by a maximum of 50% at 10⁻³ M and also had no inhibitory effect if either sodium or chloride were absent. Furosemide had no effect on the Na, K-ATPase activity or ATP levels of the TALH cells. Thus, the data suggest that 50% of the oxygen consumption of the TALH cells is related to the movement of sodium and chloride into the cell and that the ions may be transported in a coupled manner.

In addition the effect of various diuretics on oxygen consumption in the isolated TALH cells was tested. The diuretics could be grouped in three categories: (1) highly effective in inhibiting chloride-dependent oxygen consumption with an apparent inhibitory constant (K _i) of around 10⁻⁶ M, including the diuretics furosemide, bumetanide, ethacrynic acid-cysteine and piretanide, (2) diuretics which were less effective in inhibiting oxygen consumption with an apparentK _i of around 10⁻⁴ M, HOE 740 and ethacrynic acid, and (3) diuretics which were ineffective in inhibiting chloride-dependent oxygen consumption, amiloride and hydrochlorothiazide.