不依赖于Na⁺-H⁺交换的近端碳酸氢盐吸收：碳酸氢盐负荷的影响

Proximal bicarbonate absorption independent of Na+-H+ exchange: effect of bicarbonate load.

作者信息

Bank N, Aynedjian H S, Mutz B F

机构信息

Department of Medicine, Montefiore Medical Center, Bronx, New York.

出版信息

Am J Physiol. 1989 Apr;256(4 Pt 2):F577-82. doi: 10.1152/ajprenal.1989.256.4.F577.

DOI:10.1152/ajprenal.1989.256.4.F577

PMID:2539746

Abstract

To study proximal tubule bicarbonate absorption that is not due to the neutral Na+-H+ antiporter, mid to late proximal convolutions of the rat kidney were microperfused in vivo with a sodium-free choline solution containing 10(-3) M amiloride. The average sodium concentration resulting from sodium influx was 12 mM. At such low intraluminal [Na+], 10(-3) M amiloride should have inhibited the Na+-H+ antiporter by greater than 95%. When 25 mM HCO3- was in the perfusion fluid, measured total CO2 absorption was 100 pmol.mm-1.min-1. When luminal [HCO3-] was raised to 50 mM, and blood [HCO3-] was also raised to approximately 50 mM to avoid a transepithelial HCO3- concentration gradient, total CO2 absorption increased to greater than 300 pmol.mm-1.min-1. Thus raising intraluminal HCO3- concentration caused a marked increase in total CO2 absorption even though intraluminal [Na+] was low and amiloride was present. Control perfusions containing 140 mM Na+ yielded total CO2 absorption that was approximately 100 pmol.mm-1.min-1 higher than with the respective sodium-free perfusion solutions. In additional experiments, either DCCD or NEM was added to sodium-free perfusion solutions to inhibit H+-ATPase. These inhibitors reduced Na+-H+ independent total CO2 absorption markedly. Our observations suggest that under physiological acid-base conditions, sodium-independent H+ secretion can account for approximately 50% of total HCO3- absorption in mid to late proximal convolutions. This mechanism is stimulated by an increase in ambient HCO(-3) concentration to a degree that might account for the load-dependency of proximal HCO(-3) absorption in these segments of the proximal tubule.(ABSTRACT TRUNCATED AT 250 WORDS)

摘要

为了研究并非由中性钠氢交换体介导的近端小管碳酸氢盐吸收情况，在体内对大鼠肾脏中至远曲近端小管进行微灌注，灌注液为含10⁻³ M氨氯吡脒的无钠胆碱溶液。钠内流产生的平均钠浓度为12 mM。在如此低的管腔内[Na⁺]水平下，10⁻³ M氨氯吡脒应能抑制钠氢交换体超过95%。当灌注液中含有25 mM HCO₃⁻时，测得的总二氧化碳吸收量为100 pmol·mm⁻¹·min⁻¹。当管腔内[HCO₃⁻]升至50 mM，且血液[HCO₃⁻]也升至约50 mM以避免跨上皮碳酸氢盐浓度梯度时，总二氧化碳吸收量增加至超过300 pmol·mm⁻¹·min⁻¹。因此，即使管腔内[Na⁺]较低且存在氨氯吡脒，提高管腔内碳酸氢盐浓度仍会导致总二氧化碳吸收量显著增加。含有140 mM Na⁺的对照灌注所产生的总二氧化碳吸收量比相应的无钠灌注液高出约100 pmol·mm⁻¹·min⁻¹。在另外的实验中，将二环己基碳二亚胺（DCCD）或N-乙基马来酰亚胺（NEM）添加到无钠灌注液中以抑制氢-ATP酶。这些抑制剂显著降低了钠非依赖性总二氧化碳吸收。我们的观察结果表明，在生理酸碱条件下，钠非依赖性氢分泌可占中至远曲近端小管总碳酸氢盐吸收的约50%。该机制会因周围HCO₃⁻浓度升高而受到刺激，其刺激程度可能解释了近端小管这些节段中近端HCO₃⁻吸收的负荷依赖性。（摘要截选至250词）