Neural control of distal tubular bicarbonate and fluid transport

Although previous studies have shown that inhibition of proximal tubular reabsorption of bicarbonate and fluid partially accounts for bicarbonaturia and diuresis observed in the denervated kidney, the role of the distal convoluted tubule in the neural regulation of electrolyte excretion has not been defined. This study was designed to examine the effects of denervation on bicarbonate and fluid reabsorption in the distal convoluted tubules by using in situ microperfusion methods. Early distal tubules were perfused with a solution containing 15 mM bicarbonate at a rate of 12 nl/min, and fluid samples were collected from the late distal tubule. Bicarbonate concentrations were measured as total CO2 by microcalorimetry. The rate of fluid absorption (Jv) was determined using [methoxy-3H]inulin as a volume marker. Before denervation, the rate of bicarbonate absorption (JHCO3-) was 24.7 +/- 2.6 peq.min-1.mm-1, and Jv was 1.80 +/- 0.14 nl.min-1.mm-1. After denervation, marked reductions in JHCO3- (51%) and Jv (60%) were observed. In contrast, sham denervation did not affect JHCO3- or Jv significantly. Our results indicate that the distal convoluted tubule can reabsorb bicarbonate and fluid under physiological conditions. We conclude that the transport processes in this segment of the nephron are regulated by renal nerve activity.