Effect of high NaCl intake on Na+ and K+ transport in the rabbit distal convoluted tubule

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Abstract
Morphological studies have demonstrated that a chronic increase in distal Na+ delivery causes hypertrophy of the distal convoluted tubule (DCT). To examine whether high NaCl-intake also causes functional changes in the well defined DCT, we measured transmural voltage (VT), lumen-to-bath Na+ flux (JNa(LB)), and net K+ secretion (JK(net)) in DCTs obtained from control rabbits and those on high NaCl-intake diets. The lumen negativeVT was significantly greater in the high NaCl group than in the control group. The net K+ secretion (pmol mm−1 min−1) was greater in the high NaCl-intake group (54.1±13.0 vs 14.7±5.6). The K+ permeabïlities in both luminal and basolateral DCT membranes, as assessed by the K+-induced transepithelial voltage deflection inhibitable with Ba2+, were increased in the experimental group. The lumen-to-bath22Na flux (pmol mm−1 min−1) was also greater in the experimental group (726±119 vs 396±65). TheVT component inhibitable with amiloride was also elevated in the high NaCl-intake group. Furthermore, Na+−K+-ATPase activity of the DCT was higher in the experimental than in the control group. We conclude that high NaCl intake increases both Na+ reabsorption and K+ secretion by the DCT. This phenomenon is associated with an increased Na+−K+-ATPase activity along with increased Na+ and K+ permeabilities of the luminal membrane, and an increase in the K+ permeability of the basolateral membrane. Cellular mechanisms underlying these functional changes remain to be established.