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. 1986 Aug;50(2):239–252. doi: 10.1016/S0006-3495(86)83458-0

Axial heterogeneity and filtered-load dependence of proximal bicarbonate reabsorption.

H Bernstein, L J Atherton, W M Deen
PMCID: PMC1329741  PMID: 3017467

Abstract

A theoretical model was developed to examine the role of physical and chemical factors in the control of bicarbonate reabsorption in the renal proximal tubule. Included in the model were axial and radial variations in the concentrations of HCO3-, CO2 and related chemical species in the tubule lumen and epithelial cells. Relations between these concentrations and the solute fluxes across the brush border and basolateral membranes were also included, as were reaction rate and equilibrium expressions to describe the various buffering processes in the lumen and cells. The two most critical membrane parameters, the rate constant for H+ secretion at the brush border and the effective permeability of HCO3- at the basolateral membrane, were evaluated by comparing model predictions with available free-flow micropuncture data in the rat. It was found that the experimental observations could be explained only by decreasing one or both of these membrane parameters with axial position, suggesting a progressive decrease in HCO3- reabsorptive capacity along the tubule. For single nephron filtered loads of HCO3- up to about 1,400 pmol/min, absolute bicarbonate reabsorption was predicted to increase nearly in proportion to filtered load, whereas it was calculated to be relatively constant at higher filtered loads, irrespective of how filtered load was assumed to be varied. These predictions are in excellent agreement with most of the available micropuncture data in rats, as is the prediction that HCO3- reabsorption should change in parallel with CO2 partial pressure in the filtrate, at a given filtered load of HCO3-. Certain discrepancies between the model predictions and experimental observations are evident at very high filtered loads, and the implications of these are discussed in terms of possible adaptive responses of the tubule.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Alpern R. J., Cogan M. G., Rector F. C., Jr Effect of luminal bicarbonate concentration on proximal acidification in the rat. Am J Physiol. 1982 Jul;243(1):F53–F59. doi: 10.1152/ajprenal.1982.243.1.F53. [DOI] [PubMed] [Google Scholar]
  2. Alpern R. J., Cogan M. G., Rector F. C., Jr Effects of extracellular fluid volume and plasma bicarbonate concentration on proximal acidification in the rat. J Clin Invest. 1983 Mar;71(3):736–746. doi: 10.1172/JCI110821. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Alpern R. J., Cogan M. G., Rector F. C., Jr Flow dependence of proximal tubular bicarbonate absorption. Am J Physiol. 1983 Oct;245(4):F478–F484. doi: 10.1152/ajprenal.1983.245.4.F478. [DOI] [PubMed] [Google Scholar]
  4. Alpern R. J., Rector F. C., Jr A model of proximal tubular bicarbonate absorption. Am J Physiol. 1985 Feb;248(2 Pt 2):F272–F281. doi: 10.1152/ajprenal.1985.248.2.F272. [DOI] [PubMed] [Google Scholar]
  5. Aronson P. S., Nee J., Suhm M. A. Modifier role of internal H+ in activating the Na+-H+ exchanger in renal microvillus membrane vesicles. Nature. 1982 Sep 9;299(5879):161–163. doi: 10.1038/299161a0. [DOI] [PubMed] [Google Scholar]
  6. Atherton L. J., Deen W. M., Maddox D. A., Gennari F. J. Analysis of the factors influencing peritubular PCO2 in the rat. Am J Physiol. 1984 Jul;247(1 Pt 2):F61–F72. doi: 10.1152/ajprenal.1984.247.1.F61. [DOI] [PubMed] [Google Scholar]
  7. Basmadjian D., Dykes D. S., Baines A. D. Flow through brushborders and similar protuberant wall structures. J Membr Biol. 1980 Oct 31;56(3):183–190. doi: 10.1007/BF01869475. [DOI] [PubMed] [Google Scholar]
  8. Boron W. F., Boulpaep E. L. Intracellular pH regulation in the renal proximal tubule of the salamander. Basolateral HCO3- transport. J Gen Physiol. 1983 Jan;81(1):53–94. doi: 10.1085/jgp.81.1.53. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Chan Y. L., Biagi B., Giebisch G. Control mechanisms of bicarbonate transport across the rat proximal convoluted tubule. Am J Physiol. 1982 May;242(5):F532–F543. doi: 10.1152/ajprenal.1982.242.5.F532. [DOI] [PubMed] [Google Scholar]
  10. Cogan M. G. Effects of acute alterations in PCO2 on proximal HCO-3, Cl-, and H2O reabsorption. Am J Physiol. 1984 Jan;246(1 Pt 2):F21–F26. doi: 10.1152/ajprenal.1984.246.1.F21. [DOI] [PubMed] [Google Scholar]
  11. Cogan M. G., Liu F. Y. Metabolic alkalosis in the rat. Evidence that reduced glomerular filtration rather than enhanced tubular bicarbonate reabsorption is responsible for maintaining the alkalotic state. J Clin Invest. 1983 May;71(5):1141–1160. doi: 10.1172/JCI110864. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Cogan M. G., Maddox D. A., Lucci M. S., Rector F. C., Jr Control of proximal bicarbonate reabsorption in normal and acidotic rats. J Clin Invest. 1979 Nov;64(5):1168–1180. doi: 10.1172/JCI109570. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Cogan M. G., Rector F. C., Jr Proximal reabsorption during metabolic acidosis in the rat. Am J Physiol. 1982 May;242(5):F499–F507. doi: 10.1152/ajprenal.1982.242.5.F499. [DOI] [PubMed] [Google Scholar]
  14. Cortell S., Gennari F. J., Davidman M., Bossert W. H., Schwartz W. B. A definition of proximal and distal tubular compliance. Practical and theoretical implications. J Clin Invest. 1973 Sep;52(9):2330–2339. doi: 10.1172/JCI107422. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Goldman D. E. POTENTIAL, IMPEDANCE, AND RECTIFICATION IN MEMBRANES. J Gen Physiol. 1943 Sep 20;27(1):37–60. doi: 10.1085/jgp.27.1.37. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Greger R., Lang F., Marchand G., Knox F. G. Site of renal phosphate reabsorption. Micropuncture and microinfusion study. Pflugers Arch. 1977 Jun 8;369(2):111–118. doi: 10.1007/BF00591566. [DOI] [PubMed] [Google Scholar]
  17. Gros G., Moll W. Facilitated diffusion of CO2 across albumin solutions. J Gen Physiol. 1974 Sep;64(3):356–371. doi: 10.1085/jgp.64.3.356. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Gros G., Moll W., Hoppe H., Gros H. Proton transport by phosphate diffusion--a mechanism of facilitated CO2 transfer. J Gen Physiol. 1976 Jun;67(6):773–790. doi: 10.1085/jgp.67.6.773. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Harris R. C., Seifter J. L., Brenner B. M. Adaptation of Na+-H+ exchange in renal microvillus membrane vesicles. Role of dietary protein and uninephrectomy. J Clin Invest. 1984 Dec;74(6):1979–1987. doi: 10.1172/JCI111619. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Jacobson H. R. Effects of CO2 and acetazolamide on bicarbonate and fluid transport in rabbit proximal tubules. Am J Physiol. 1981 Jan;240(1):F54–F62. doi: 10.1152/ajprenal.1981.240.1.F54. [DOI] [PubMed] [Google Scholar]
  21. Liu F. Y., Cogan M. G. Axial heterogeneity in the rat proximal convoluted tubule. I. Bicarbonate, chloride, and water transport. Am J Physiol. 1984 Nov;247(5 Pt 2):F816–F821. doi: 10.1152/ajprenal.1984.247.5.F816. [DOI] [PubMed] [Google Scholar]
  22. Maddox D. A., Atherton L. J., Deen W. M., Gennari F. J. Proximal HCO3- reabsorption and the determinants of tubular and capillary PCO2 in the rat. Am J Physiol. 1984 Jul;247(1 Pt 2):F73–F81. doi: 10.1152/ajprenal.1984.247.1.F73. [DOI] [PubMed] [Google Scholar]
  23. Maddox D. A., Gennari F. J. Proximal tubular bicarbonate reabsorption and PCO2 in chronic metabolic alkalosis in the rat. J Clin Invest. 1983 Oct;72(4):1385–1395. doi: 10.1172/JCI111095. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Maren T. H. Carbon dioxide equilibria in the kidney: the problems of elevated carbon dioxide tension, delayed dehydration, and disequilibrium pH. Kidney Int. 1978 Nov;14(5):395–405. doi: 10.1038/ki.1978.144. [DOI] [PubMed] [Google Scholar]
  25. Wang K. W., Deen W. M. Chemical kinetic and diffusional limitations on bicarbonate reabsorption by the proximal tubule. Biophys J. 1980 Aug;31(2):161–182. doi: 10.1016/S0006-3495(80)85048-X. [DOI] [PMC free article] [PubMed] [Google Scholar]

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