The effect of 10(-3) M-dinitrophenol (DNP) on renal tubular acidification was studied in proximal tubules of rat kidneys perfused with mammalian Ringer solution. Alkaline (pH 7.8) or acid (pH 5.8) phosphate-buffered solutions were injected into the lumen, and pH changes recorded with antimony micro-electrodes. Luminal perfusion with DNP caused complex acidification or alkalinization curves, an initial rapid shift toward a higher than control pH being followed by a slower acidification. Acidification half-times of the initial phase (t1/2 = 1.6 s) were markedly shorter than controls (6.2 s). This response was probably due to transient action of DNP, since keeping constant peritubular DNP levels by capillary perfusion caused simple exponential pH curves. In such experiments luminal pH increased from pH 6.6-6.8 to 7.1-7.2, while acidification and alkalinization t1/2 decreased from about 7 s to 3-5 s. Secretory H-ion fluxes increased transiently and then fell below controls after a few minutes of perfusion, while H-ion efflux from the lumen increased progressively. These data suggest that, besides its known effect on cell metabolism, DNP acts directly on proximal tubular cell membranes, increasing the rate of passive H-ion equilibration, both mechanisms impairing the tubular capacity to maintain normal proximal pH gradients and fluxes.
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