Mechanisms of proximal proton secretion in BBM of herbivorous, omnivorous, and carnivorous species

The mechanisms of proton secretion by the proximal brush-border membrane (BBM) were compared in carnivorous (dog), omnivorous (human, pig, rat), and herbivorous (rabbit, hamster) species. The activity of the proton pump (V-type bafilomycin-sensitive H(+)-adenosinetriphosphatase) and of the Na+/H+ exchanger (amiloride-sensitive quenching of acridine orange fluorescence), the two major proton secretion mechanisms, was measured. The enzymatic activity of the H(+)-adenosinetriphosphatase activity was measured in intact (endosomes) and solubilized (0.1% deoxycholate or Triton X-100) BBM vesicles isolated by conventional Mg2+ precipitation techniques. In all species, but not in humans, the fraction of the ATP turnover energizing the proton pump (bafilomycin-sensitive respiration) was also measured in isolated proximal tubules. Significant differences in acid transport mechanisms were noted between species, with the proton pump predominating in the BBM of carnivorous species and the Na+/H+ exchanger predominating in the BBM of herbivorous species. The fraction of respiration suppressible by bafilomycin in proximal tubules was also different in all the species considered. This may indicate a different organization of proximal H+ transport related to the species-specific menace to acid-base balance.

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Role of iNOS and eNOS in modulating proximal tubule transport and acid-base balance

AJP Renal Physiology ◽

10.1152/ajprenal.00243.2001 ◽

2002 ◽

Vol 283 (4) ◽

pp. F658-F662 ◽

Cited By ~ 35

Author(s):

Tong Wang

Keyword(s):

Proximal Tubule ◽

Knockout Mice ◽

Proximal Tubules ◽

Wild Type ◽

Acid Base Balance ◽

Acid Base ◽

Base Balance ◽

Acid Base Status ◽

Inos Knockout Mice ◽

Oxide Synthase

Our laboratory has previously shown that mice lacking neuronal nitric oxide synthase (nNOS) are defective in fluid absorption ( J v) and HCO[Formula: see text]absorption ( J HCO3) in the proximal tubule and develop metabolic acidosis. The present study examined the transport of fluid and HCO[Formula: see text] in the proximal tubule and acid-base status in mice lacking two other isoforms of NOS, inducible NOS (iNOS) and endothelial NOS (eNOS). Proximal tubules were microperfused in situ in wild-type and NOS knockout mice by methods previously described (Wang T, Yang C-L, Abbiati T, Schultheis PJ, Shull GE, Giebisch G, and Aronson PS. Am J Physiol Renal Physiol 277: F298–F302, 1999). [3H]inulin and total CO2 concentrations were measured in the perfusate and collected fluid, and net J v and J HCO3 were analyzed. These data show that J HCO3 was 35% lower (71.7 ± 6.4 vs. 109.9 ± 7.3 pmol · min−1 · mm−1, n = 13, P < 0.01) and J v was 38% lower (0.95 ± 0.15 vs. 1.54 ± 0.17 nl · min−1 · mm−1, n = 13, P < 0.05) in iNOS knockout mice compared with their wild-type controls. Addition of the iNOS-selective inhibitor l- N 6-(1-iminoethyl) lysine, reduced both J v and J HCO3 significantly in wild-type, but not in iNOS knockout, mice. In contrast, both J HCO3(93.3 ± 7.9 vs. 110.6 ± 6.18 pmol · min−1 · mm−1) and J v (1.56 ± 0.17 vs. 1.55 ± 0.16 nl · min−1 · mm−1) did not change significantly in eNOS knockout mice. These results indicated that iNOS upregulates Na+ and HCO[Formula: see text]transport, whereas eNOS does not directly modulate Na+ and HCO[Formula: see text] transport in the kidney proximal tubules.

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Glutamine synthesis is heterogeneous and differentially regulated along the rabbit renal proximal tubule

Biochemical Journal ◽

10.1042/bj3370543 ◽

1999 ◽

Vol 337 (3) ◽

pp. 543-550 ◽

Cited By ~ 3

Author(s):

Bernard FERRIER ◽

Agnès CONJARD ◽

Mireille MARTIN ◽

Gabriel BAVEREL

Keyword(s):

Proximal Tubule ◽

Proximal Tubules ◽

Synthetase Activity ◽

Glutamine Synthetase Activity ◽

Dependent Manner ◽

Acid Base Balance ◽

Physiological Concentration ◽

Nephron Segment ◽

Base Balance ◽

Glutamine Synthesis

Glutamine synthesis, a major process for ammonia detoxification and the control of acid–base balance, occurs from various precursors in suspensions of rabbit proximal tubules. However, no data are currently available on the distribution of glutamine synthesis along the rabbit proximal tubule, and its modulation by changes of substrate concentration. Therefore we have microdissected and incubated the three parts (S1, S2 and S3) of rabbit proximal tubules and measured glutamine synthesis from alanine and aspartate. With a physiological concentration of alanine (0.25 mM) or aspartate (0.05 mM), glutamine synthesis in the S1 segment was about half of that in the S2 and S3 segments, and was greater from alanine than from aspartate along the entire proximal tubule. Elevation of alanine and aspartate concentrations to 5 mM increased glutamine synthesis in both a substrate- and segment-dependent manner. It is concluded that glutamine synthesis occurs from alanine and aspartate along the entire rabbit proximal tubule; however, contrary to what might have been expected on the basis of measurement of glutamine synthetase activity, the basal rate of glutamine synthesis and its adaptation to increased substrate availability are heterogeneous along this nephron segment.

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Higher Dietary Acidity is Associated with Lower Bone Mineral Density in Postmenopausal Iranian Women, Independent of Dietary Calcium Intake

International Journal for Vitamin and Nutrition Research ◽

10.1024/0300-9831/a000207 ◽

2014 ◽

Vol 84 (3-4) ◽

pp. 0206-0217 ◽

Cited By ~ 8

Author(s):

Seyedeh-Elaheh Shariati-Bafghi ◽

Elaheh Nosrat-Mirshekarlou ◽

Mohsen Karamati ◽

Bahram Rashidkhani

Keyword(s):

Calcium Intake ◽

Dietary Calcium ◽

Dietary Calcium Intake ◽

Dietary Intakes ◽

Iranian Women ◽

Acid Base Balance ◽

Mineral Density ◽

Acid Base ◽

Base Balance ◽

Dietary Acid

Findings of studies on the link between dietary acid-base balance and bone mass are relatively mixed. We examined the association between dietary acid-base balance and bone mineral density (BMD) in a sample of Iranian women, hypothesizing that a higher dietary acidity would be inversely associated with BMD, even when dietary calcium intake is adequate. In this cross-sectional study, lumbar spine and femoral neck BMDs of 151 postmenopausal women aged 50 - 85 years were measured using dual-energy x-ray absorptiometry. Dietary intakes were assessed using a validated food frequency questionnaire. Renal net acid excretion (RNAE), an estimate of acid-base balance, was then calculated indirectly from the diet using the formulae of Remer (based on dietary intakes of protein, phosphorus, potassium, and magnesium; RNAERemer) and Frassetto (based on dietary intakes of protein and potassium; RNAEFrassetto), and was energy adjusted by the residual method. After adjusting for potential confounders, multivariable adjusted means of the lumbar spine BMD of women in the highest tertiles of RNAERemer and RNAEFrassetto were significantly lower than those in the lowest tertiles (for RNAERemer: mean difference -0.084 g/cm2; P=0.007 and for RNAEFrassetto: mean difference - 0.088 g/cm2; P=0.004). Similar results were observed in a subgroup analysis of subjects with dietary calcium intake of >800 mg/day. In conclusion, a higher RNAE (i. e. more dietary acidity), which is associated with greater intake of acid-generating foods and lower intake of alkali-generating foods, may be involved in deteriorating the bone health of postmenopausal Iranian women, even in the context of adequate dietary calcium intake.

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