Acid extrusion in S3 segment of rabbit proximal tubule. II. Effect of basolateral CO2/HCO3-.
Monitoring intracellular absorbance spectra of the pH-sensitive dye dimethylcarboxyfluorescein we studied intracellular pH (pHi) regulation in the isolated perfused S3 segment of the rabbit proximal tubule. In the preceding study [Am. J. Physiol. 268 (Renal Fluid Electrolyte Physiol. 37): F179-F192, 1995.], we demonstrated that simultaneously adding CO2/HCO3- to both lumen and bath stimulated two acid-extruding mechanisms, one dependent on luminal Na+ (a Na+/H+ exchanger) and one independent of Na+ (presumably a H+ pump). Here, we examine the effects of adding CO2/HCO3- to the lumen only or to the bath only. Over a broad pHi range, the total rate of pHi recovery from an acid load in the presence of Na+ was not increased by luminal CO2/HCO3-. On the other hand, basolateral CO2/HCO3- increased the pHi recovery rate to an even greater extent than had bilateral CO2/HCO3-. Regarding the Na(+)-independent pHi recovery mechanism, we found that luminal CO2/HCO3- failed to increase the pHi recovery rate compared with controls also studied in the absence of Na+. Neither did luminal CO2/HCO3- significantly affect the lag time between the maximal acid load and the initiation of the Na(+)-independent pHi recovery (approximately 147 vs. approximately 212 s in controls). On the other hand, adding CO2/HCO3- to only the bath substantially increased the rate of Na(+)-independent pHi recovery, which generally was greater than that observed with bilateral CO2/HCO3-. CO2/HCO3- only in the bath also reduced the lag time to approximately 51 s, which is not significantly different from the value of approximately 36 s observed with bilateral CO2/HCO3-. Our data are consistent with the hypothesis that basolateral (but not luminal) CO2/HCO3- stimulates both a luminal Na+/H+ exchanger and a luminal H+ pump.
Chen
L K
LK
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
Boron
W F
WF
D000143:Acids / Q000378:metabolism*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D005260:Female; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology
D000143:Acids; D001639:Bicarbonates; D002245:Carbon Dioxide; D012964:Sodium