Studies on the mechanism whereby acidemia stimulates collecting duct hydrogen ion secretion in vivo

Studies on the mechanism whereby acidemia stimulates collecting duct hydrogen ion secretion in vivo. The purpose of these studies was to elucidate the mechanism whereby collecting duct hydrogen ion secretion was augmented by acidemia. The urine minus blood P CO 2 difference in alkaline urine (U-B P CO 2 ) was used to evaluate this parameter. In dogs with a normal ECF volume, the U-B P CO 2 was high, and there was no significant relationship between the U-B P CO 2 factored for the urine bicarbonate concentration and the blood hydrogen ion concentrations unless amiloride, an agent that abolishes the transtubular potential difference, was present. In this latter case, the U-B P CO 2 was a linear function of the urine bicarbonate concentration, and the U-B P CO 2 factored for the urine bicarbonate concentration was directly proportional to the blood hydrogen ion concentration. To extend the pH range considerably, we used lysine to induce bicarbonaturia in dogs with an expanded ECF volume. Amiloride now caused only a small decrease in the U-B P CO 2 at any urine bicarbonate concentration, and furthermore, it did not influence the linear relationship between the U-B P CO 2 factored for the urine bicarbonate concentration and the blood hydrogen ion concentration. These results suggest that acidemia stimulates collecting duct hydrogen ion secretion by a mechanism that appears to be independent of the amiloride-sensitive component of the U-B P CO 2 . We speculate that the mechanism might involve an increased intracellular hydrogen ion concentration during acidemia. Etude du mecanisme par lequel l'acidemie stimule la secretion d'ion hydrogene par le canal collecteur in vivo. Le but de ce travail est d'elucider le mecanisme par lequel la secretion d'ion hydrogene est augmentee par l'acidemie. La difference urine-sang de P CO 2 en urine alcaline (U-B P CO 2 ) a ete utilisee pour evaluer ce parametre. Chez des chiens avec un volume extracellulaire (ECF) normal, la difference U-B P CO 2 est elevee et il n'y a pas de relation significative entre cette difference rapportee a la concentration urinaire de bicarbonate et la concentration sanguine d'ion hydrogene sauf quand de l'amiloride, un agent qui abolit la difference de potentiel transtubulaire, est administre. Dans ce cas la difference U-B P CO 2 est une fonction lineaire de la concentration urinaire de bicarbonate et U-B P CO 2 rapportee a la concentration de bicarbonate urinaire est directement proportionnelle a la concentration sanguine d'ion hydrogene. Afin d'etendre considerablement l'eventail de pH la lysine a ete employee pour determiner une bicarbonaturie chez le chien dont le volume extracellulaire est augmente. Dans cette situation, l'amiloride ne determine qu'une faible diminution de U-B P CO 2 a n'importe quelle concentration urinaire de bicarbonate, et, de plus, il n'influence pas la relation lineaire entre U-B P CO 2 rapportee a la concentration de bicarbonate urinaire et la concentration sanguine d'ion hydrogene. Ces resultats suggerent que l'acidemie stimule la secretion d'ion hydrogene par le canal collecteur par un mecanisme qui parait independant de la composante sensible a l'amiloride de U-B P CO 2 . Nous faisons l'hypothese que ce mecanisme peut impliquer une augmentation de la concentration intracellulaire d'ion hydrogene au cours de l'acidemie.