TY - JOUR
T1 - Microelectrode determination of pH and PCO2 in rat proximal tubule after benzolamide
T2 - Evidence for hydrogen ion secretion
AU - DuBose, T. D.
AU - Pucacco, L. R.
AU - Seldin, D. W.
AU - Carter, N. W.
AU - Kokko, J. P.
N1 - Funding Information:
Portions of this study were presented at the VII International Congress of Nephrology, Montreal, June 18-23, 1978, and at the 11th Annual Meeting of the American Society of Nephrology, New Orleans, November 19-21, 1978. This work was supported in part by NIAMDD Grant I RO1 AM14677. Mr. J. Green and Mrs. J. Cutrer gave technical assistance, and Ms. K. Williams gave secretarial assistance. During this study, Dr. Pucacco was a graduate stu- dent in the Biomedical Engineering Program at Southern Methodist University.
PY - 1979
Y1 - 1979
N2 - Previous micropuncture studies supporting hydrogen secretion as the mechanism of bicarbonate reabsorption have relied on the demonstration of an acid disequilibrium pH in the proximal tubule after systemic administration of a carbonic anhydrase inhibitor. Previous calculations of disequilibrium pH, however, have involved the necessary assumption that PCO2 in the proximal convoluted tubule was equal to arterial blood PCO2. This assumption can no longer be supported in view of the recent demonstration that the PCO2 in proximal and distal tubular fluid exceeded arterial blood by approximately 25 mm Hg. The purpose of the present study was to determine directly pH and PCO2 with microelectrodes in both the early and late segments of the accessible proximal tubule of nine Sprague-Dawley rats before and after administration of benzolamide (2.0 mg/kg/hr, i.v.). In the early proximal tubule, pH decreased significantly after benzolamide administration from 6.98 ± 0.03 to 6.62 ± 0.03 pH U (P < 0.001), and PCO2 also decreased from 65.1 ± 1.2 to 59.3 ± 1.4 mm Hg (P < 0.005). In the late proximal convoluted tubule, pH did not change after benzolamide (6.75 ± 0.02 to 6.77 ± 0.02), but PCO2 decreased significantly (64.3 ± 1.5 to 57.7 ± 1.6) (P < 0.01). We conclude: (1) the fall in both pH and PCO2 in the early proximal tubule indicates that carbonic acid, not carbon dioxide accumulates after inhibition of luminal carbonic anhydrase; (2) although PCO2 also decreased in the late proximal tubule, unlike the early segment, pH was unchanged after benzolamide administration, perhaps as a result of increased bicarbonate delivery; and (3) PCO2 in vivo was significantly greater than was systemic arterial PCO2 before and after benzolamide administration in both the early and late proximal convoluted tubule. These findings lend support to the view that bicarbonate reabsorption in the proximal convoluted tubule occurs, in part, by hydrogen secretion.
AB - Previous micropuncture studies supporting hydrogen secretion as the mechanism of bicarbonate reabsorption have relied on the demonstration of an acid disequilibrium pH in the proximal tubule after systemic administration of a carbonic anhydrase inhibitor. Previous calculations of disequilibrium pH, however, have involved the necessary assumption that PCO2 in the proximal convoluted tubule was equal to arterial blood PCO2. This assumption can no longer be supported in view of the recent demonstration that the PCO2 in proximal and distal tubular fluid exceeded arterial blood by approximately 25 mm Hg. The purpose of the present study was to determine directly pH and PCO2 with microelectrodes in both the early and late segments of the accessible proximal tubule of nine Sprague-Dawley rats before and after administration of benzolamide (2.0 mg/kg/hr, i.v.). In the early proximal tubule, pH decreased significantly after benzolamide administration from 6.98 ± 0.03 to 6.62 ± 0.03 pH U (P < 0.001), and PCO2 also decreased from 65.1 ± 1.2 to 59.3 ± 1.4 mm Hg (P < 0.005). In the late proximal convoluted tubule, pH did not change after benzolamide (6.75 ± 0.02 to 6.77 ± 0.02), but PCO2 decreased significantly (64.3 ± 1.5 to 57.7 ± 1.6) (P < 0.01). We conclude: (1) the fall in both pH and PCO2 in the early proximal tubule indicates that carbonic acid, not carbon dioxide accumulates after inhibition of luminal carbonic anhydrase; (2) although PCO2 also decreased in the late proximal tubule, unlike the early segment, pH was unchanged after benzolamide administration, perhaps as a result of increased bicarbonate delivery; and (3) PCO2 in vivo was significantly greater than was systemic arterial PCO2 before and after benzolamide administration in both the early and late proximal convoluted tubule. These findings lend support to the view that bicarbonate reabsorption in the proximal convoluted tubule occurs, in part, by hydrogen secretion.
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U2 - 10.1038/ki.1979.82
DO - 10.1038/ki.1979.82
M3 - Article
C2 - 37362
AN - SCOPUS:0018647541
SN - 1744-165X
VL - 15
SP - 624
EP - 629
JO - Seminars in Fetal and Neonatal Medicine
JF - Seminars in Fetal and Neonatal Medicine
IS - 6
ER -