The Regulation of Renal Bicarbonate Reabsorption by Plasma Carbon Dioxide Tension 1

The Role of Plasma Co2 Tension and Carbonic Anhydrase Activity in the Renal Reabsorption of Bicarbonate*

“…Unlike previous studies (1)(2)(3), it is apparent from Figure 1 that increasing plasma pCO, accelerates HCO,-reabsorption in curvilinear fashion. Although the curve tends to become flat at higher CO2 tensions, a point was never reached Inhibition of red cell carbonic anhydrase prevented the lowering of the plasma pCO., below 30 mm Hg.…”

“…Second, the reabsorption of large amounts of filtrate will sweep H2C03 back into the cell through aqueous-filled pores as a result of solvent drag. This recycling of H2C03 back into the cell completes the process of HC03-reabsorption initiated by the secretion of H' and at the same time markedly reduces the need for high rates of H2C03 formation from the uncatalyzed hydration of CO2.2 2 In a cyclic process such as this the rate at which H2CO3 must be produced from CO2, in order to accomplish the observed rates of HCOG3 reabsorption, needs only be as great as the rate at which H2CO is lost from the cycle by decomposition in the tubular lumen. If, therefore, only 75 per cent of the luminal H2CO, returned to the cell by diffusion and solvent drag and the remaining 25 per cent decomposed to CO2 and H20, then only 25 per cent of the H+ mediating HCO3-reabsorption need be produced from CO2.…”

“…Two of the principal determinants of H' secretion thus far identified are the CO, tension of plasma (1)(2)(3) and the activity of the carbonic anhydrase enzyme system (11). Plasma pCO2 is thought to influence HC03-reabsorption by altering the production of H' ions, predominantly via the catalyzed hydration of CO2.…”

“…The reabsorption of bicarbonate by the kidneys under normal circumstances appears to be a linear function of the plasma CO, tension (1)(2)(3). PreviOtis studies from this laboratory (4) (lemonstratel that when carbonic anhydrase was inhibited by acetazolamide the linear relationship between plasma CO2 tension and HCO,-reabsorption still obtained.…”

Effect of acute hypercapnia on renal and proximal tubular total carbon dioxide reabsorption in the acetazolamide-treated rat.

“…Many clearance studies have documented that acute hypercapnia (AHC)' enhances the maximal bicarbonate reabsorptive capacity of the kidney and decreases fractional bicarbonate excretion (2)(3)(4)(5). It has also been shown that AHC can augment renal bicarbonate reabsorption in the presence ofpharmacologic inhibitors of renal carbonic anhydrase such as acetazolamide (ACTZ).…”