Laboratory Investigation

Kidney International (1981) 20, 636–642; doi:10.1038/ki.1981.187

Studies on the regulation of hydrogen ion secretion in the collecting duct in vivo: Evaluation of factors that influence the urine minus blood PCO2 difference

Siu-Cheung Tam, Marc B Goldstein, Bobby J Stinebaugh, Ching-Bun Chen, André Gougoux and Mitchell L Halperin

Renal Divisions, Universities of Toronto and Montreal, Canada, and Baylor College of Medicine, Houston, Texas

Correspondence: Dr M L Halperin, St. Michael's Hospital, Lab #1, Research Wing, 38 Shuter Street Annex, Toronto, Ontario, Canada, M5B 1A6

Received 5 November 1980; Revised 4 March 1981.

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Abstract

Studies on the regulation of hydrogen ion secretion in the collecting duct in vivo: Evaluation of factors that influence the urine minus blood PCO2 difference. The purpose of these studies was to clarify the basis of the relationship between the urine bicarbonate concentration and the urine minus blood PCO2 difference in alkaline urine (U-B PCO2) and hence shed light on factors that influence hydrogen ion secretion in the collecting duct in vivo. The U-B PCO2 was used to monitor this latter parameter. In dogs with a normal extracellular fluid (ECF) volume, the U-B PCO2 was not primarily influenced by the urine bicarbonate concentration but rather it was related to the rate of sodium excretion. The U-B PCO2 could be abolished by amiloride when the urine bicarbonate concentration was less than 60 mM. At higher urine bicarbonate concentrations, there was a linear correlation between the U-B PCO2 and the urine bicarbonate concentration in normovolemic dogs given amiloride, but the .absolute values were lower than they were in normovolemic animals not treated with amiloride. In the dogs with an expanded ECF volume, the U-B PCO2 was lower than it was in the normovolemic animals, and the U-B PCO2 was now directly related to the urine bicarbonate concentration and not influenced by the rate of sodium excretion. Amiloride had little influence on the U-B PCO2 under these conditions. These results are interpreted to suggest that the magnitude of collecting duct hydrogen ion secretion is determined primarily by the electrical gradient generated by sodium reabsorption in normovolemic dogs and by the intracellular and lumenal hydrogen ion concentrations when the ECF volume is expanded or when active sodium reabsorption is inhibited by amiloride.

Etude de la régulation de la sécrétion d'ion hydrogène dans le canal collecteur in vivo: Évaluation des facteurs qui influencent la différence de PCO2 entre l'urine et le sang. Le but de ce travail est de clarifier la base de la relation entre la concentration de bicarbonate de l'urine et la différence de PCO2 entre l'urine et le sang en urine alcaline (U-B PCO2) et par conséquent d'identifier les facteurs qui influencent la sécrétion d'ion hydrogène par le canal collecteur in vivo. U-B PCO2 a été utilisée pour suivre ce dernier paramètre. Chez des chiens dont le volume extracellulaire est normal U-B PCO2 n'est pas influencée par la concentration de bicarbonate urinaire, mais est plutôt liée au débit d'excrétion de sodium. U-B PCO2 peut être abolie par l'amiloride quand la concentration urinaire de bicarbonate est inférieure à 60 mM. Aux concentrations urinaires de bicarbonate plus élevées, il y a une relation linéaire entre U-B PCO2 et la concentration urinaire de bicarbonate chez des chiens normovolémiques recevant de l'amiloride, mais les valeurs absolues sont inférieures à celles des animaux normovolémiques non traités par l'amiloride. Chez les chiens dont le volume extracellulaire est augmenté, la différence U-B PCO2 est inférieure à celle des animaux normovolémiques, directement liée à la concentration de bicarbonate urinaire et non influencée par le débit d'excrétion de sodium. L'amiloride a peu d'influence sur U-B PCO2 dans ces conditions. Ces résultats suggèrent que l'importance de la sécrétion d'ion hydrogène par le canal collecteur est essentiellement déterminée par le gradient électrique engendré par la réabsorption de sodium chez le chien normovolémique et par les concentrations intracellulaire et luminale d'ion hydrogène quand le volume extracellulaire est augmenté ou quand la réabsorption active de sodium est inhibée par l'amiloride.

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