Ontogeny of Na+/H+ Antiporter Activity in Rat Proximal Convoluted Tubules

Shah, Mehul; Gupta, Neena; Dwarakanath, Vangipuram; Moe, Orson W.; Baum, Michel

doi:10.1203/00006450-200008000-00014

Cited by 43 publications

(77 citation statements)

References 33 publications

(63 reference statements)

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“…Neonatal, thyroid-treated neonatal and adult proximal tubule proteins (100 μg/lane) were denatured and then separated on a 6% polyacrylamide gel using SDS-PAGE as previously described (20,21). The proteins were transferred overnight to a polyvinylidene diflouride membrane at 120-140 mA at 4°C.…”

Section: Sds-page and Immunoblottingmentioning

confidence: 99%

Developmental Changes in Proximal Tubule Tight Junction Proteins

et al. 2005

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We demonstrated previously that neonatal proximal tubules have a lower passive paracellular permeability to chloride ions and higher resistance than that of adult proximal tubules. In addition, administration of thyroid hormone to neonates, before the normal maturational increase in serum thyroid hormone levels, prematurely accelerates the developmental increase in chloride permeability to adult levels. To test the hypothesis that there is a maturational change in tight junction proteins and that thyroid hormone mediates these changes, we examined the two known tight junction proteins present in proximal tubules, occludin and claudin 2. Using immunoblot and immunohistochemistry, we demonstrated that claudin 2 has a 4-fold greater abundance in neonatal proximal tubules than in adult tubules. Occludin, however, has a 4-fold greater expression in adult tubules than in neonatal tubules. Administration of thyroid hormone to neonates did not affect claudin 2 expression, occludin expression, or the transepithelial resistance in rat proximal tubule cells in vitro. In conclusion, there are postnatal maturational changes in tight junction proteins. The factors that cause these maturational changes are unknown but unlikely to be due solely to the maturational increase in thyroid hormone.The proximal tubule receives an ultrafiltrate from the glomerulus and reabsorbs two thirds of the ultrafiltrate in a nearly iso-osmotic manner. In addition to active transcellular fluid transport, the proximal tubule reabsorbs solutes via passive diffusion across the paracellular pathway. The early proximal tubule reabsorbs glucose and amino acids and preferentially reabsorbs bicarbonate over chloride ions (1,2), which leaves the luminal fluid delivered to the late proximal tubule with a higher chloride concentration and lower bicarbonate concentration than that in the peritubular plasma (1,2). Passive solute transport is dependent on the gradients that develop between lumen and peritubular capillary and permeability properties of the paracellular pathway.Approximately two thirds of the filtered chloride is reabsorbed by the adult proximal tubule (1,3 active and transcellular and half is passive and paracellular (3-5). Active NaCl transport is mediated by the parallel operation of the Na+/H+ exchanger and a Cl−/base exchanger (3,4). Passive Cl absorption is mediated by diffusion of chloride ions down its concentration gradient generated in the early proximal tubule (6,7). Thus, the permeability properties of the paracellular pathway can affect a significant amount of proximal tubule NaCl transport.Furthermore, the permeability properties of the paracellular pathway serve as a barrier to prevent the back diffusion of glucose, amino acids, phosphate, bicarbonate, and other solutes that are in higher concentration in the peritubular fluid than in the lumen of the late proximal tubule. In previous in vitro rabbit microperfusion studies, our laboratory demonstrated that unlike the adult segment, the neonatal proximal tubule was impermeab...

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Section: Sds-page and Immunoblottingmentioning

confidence: 99%

Developmental Changes in Proximal Tubule Tight Junction Proteins

et al. 2005

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“…Steady-state pH i values were reached within 1 min after a luminal fluid exchange, but pH i was measured for several minutes to ensure a steady-state pH i was achieved. Na + /H + antiporter activity was measured as previously described in adult rat PCT perfused in vivo and neonatal and adult rabbit and rat PCT perfused in vitro (1,4,11,23,36,37). Neonatal and adult rat tubules were perfused with an ultrafiltrate-like solution without glucose and amino acids (solution B).…”

Section: Measurement Of Proton Flux Ratesmentioning

confidence: 99%

“…The bathing solution was exchanged at a rate of at least 5 ml/min. Under these conditions, changes in pH i in response to a change in luminal sodium concentration are a measure of Na + /H + antiporter activity (4,15,36,37). In the experimental period, luminal sodium was removed (solution C).…”

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Maturation of the Na⁺/H⁺antiporter (NHE3) in the proximal tubule of the hypothyroid adrenalectomized rat

Gupta¹,

Dwarakanath²,

Baum³

2004

American Journal of Physiology-Renal Physiology

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In previous studies examining the role of glucocorticoids and thyroid hormone on the maturation of the Na + /H + antiporter (NHE3), we found attenuation in the maturational increase in proximal tubule apical Na + /H + antiporter activity but no change in NHE3 mRNA abundance in either glucocorticoid-deficient or hypothyroid rats. In addition, prevention of the maturational increase in either hormone failed to totally prevent the maturational increase in Na + /H + antiporter activity. We hypothesized that one hormone played a compensatory role when the other was deficient. The present study examined whether combined deficiency of thyroid and glucocorticoid hormones would completely prevent the maturation of the Na + /H + antiporter. Adrenalectomy was performed in 9-day-old hypothyroid Sprague-Dawley rats, a time before the normal postnatal maturational increase in these hormones occurs. Nine-and 30-day-old adrenalectomized (ADX), hypothyroid rats had comparable NHE3 mRNA abundance, which was 5-to 10-fold less than 30-day-old ADX, hypothyroid rats that received corticosterone-thyroxine replacement and 30-day-old sham control rats (P < 0.05). Brush-border membrane NHE3 protein abundance was comparable in 9-and 30-day-old ADX, hypothyroid groups and ~20-fold lower than both the 30-day replacement and 30-day sham groups (P < 0.05). Similarly, the replacement and sham groups had higher sodium-dependent proton secretion than 9-and 30-day-old ADX, hypothyroid groups (P < 0.05). We conclude that combined deficiency of both hormones totally prevents the maturational increase in NHE3 mRNA and protein abundance and Na + /H + antiporter activity. Keywords NHE3; adrenalectomy; renal development; microperfusion; cell pHNeonates have a lower bicarbonate threshold than adults (21), which is due in large part to immaturity of neonatal proximal tubule acidification (10,11,35). There is a fourfold increase in rat apical membrane proximal convoluted tubule Na + /H + antiporter activity The levels of both glucocorticoids and thyroid hormone are lower in the first 1-2 wk of life compared with those of adults (24,39). The maturational increase in these hormones parallels the maturational increase in NHE3 (36), the predominant Na + /H + antiporter isoform on the apical membrane of the proximal tubule (15, 40, 41), and Na + /H + antiporter activity (36). We examined previously the role of glucocorticoids and thyroid hormone in mediating the increase in Na + /H + antiporter activity (8,23). In these studies, we either prevented the maturational increase in glucocorticoids or thyroid hormone at a time well before the normal increase during postnatal development. We found that preventing the maturational increase in either thyroid hormone or glucocorticoids suppressed the maturational increase in Na + /H + antiporter activity and brush-border membrane NHE3 protein abundance without any effect on the basal level of NHE3 mRNA abundance (8,23). Furthermore, the rate of Na + /H + antiporter activity in both adrenalectomized and hypothyro...

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“…A Nikon Eclipse TE 2000-U inverted epifluorescent microscope equipped with a Photometrics Cascade:512F microscopy camera (Ottobrunn, Germany) and Lambda DG-4/DG-5 illumination system (Sutter Instrument, Novato, CA) was used to measure intracellular pH (pH i). Tubules were incubated with the acetoxymethyl derivative of the pH-sensitive dye BCECF (BCECF-AM; 5 ϫ 10 Ϫ6 M; Molecular Probes, Eugene, OR), which is permeable across cell membranes (1,4,12,26). Intracellular esterases cleave the acetoxymethyl group, trapping BCECF in cells.…”

Section: /Nhe8mentioning

confidence: 99%

Proximal tubule Na⁺/H⁺ exchanger activity in adult NHE8^−/−, NHE3^−/−, and NHE3^−/−/NHE8^−/− mice

Baum

Twombley

Gattineni

et al. 2012

American Journal of Physiology-Renal Physiology

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NHE3 is the predominant Na+/H+ exchanger on the brush-border membrane (BBM) of the proximal tubule in adults. However, NHE3 null mice still have significant renal BBM Na+/H+ activity. NHE8 has been localized to the BBM of proximal tubules and is more highly expressed in neonates than adult animals. The relative role of NHE8 in adult renal H+ transport is unclear. This study examined whether there was compensation by NHE8 in NHE3−/− mice and by NHE3 in NHE8−/− mice. NHE3−/− mice had significant metabolic acidosis, and renal BBM NHE8 protein abundance was greater in NHE3−/− mice than control mice, indicating that there may be compensation by NHE8 in NHE3−/− mice. NHE8−/− mice had serum bicarbonate levels and pH that were not different from controls. NHE3 protein expression on the BBM was greater in NHE8−/− mice than in wild-type mice, indicating that there may be compensation by NHE3 in NHE8−/− mice. Both BBM NHE3 and NHE8 protein abundance increased in response to acidosis. Blood pressure and Na+/H+ exchanger activity were comparable in NHE8−/− mice to that of controls, but both were significantly lower in NHE3−/− mice compared with control mice. Compared with NHE3−/− mice, NHE3−/−/NHE8−/− mice had lower blood pressures. While serum bicarbonate was comparable in NHE3−/− mice and NHE3−/−/NHE8−/− mice, proximal tubule Na+/H+ exchange activity was less in NHE3−/−/NHE8−/− mice compared with NHE3−/− mice. In conclusion, NHE3 is the predominant Na+/H+ exchanger in adult mice. NHE8 may play a compensatory role in renal acidification and blood pressure regulation in NHE3−/− mice.

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Ontogeny of Na+/H+ Antiporter Activity in Rat Proximal Convoluted Tubules

Cited by 43 publications

References 33 publications

Developmental Changes in Proximal Tubule Tight Junction Proteins

Developmental Changes in Proximal Tubule Tight Junction Proteins

Maturation of the Na⁺/H⁺antiporter (NHE3) in the proximal tubule of the hypothyroid adrenalectomized rat

Proximal tubule Na⁺/H⁺ exchanger activity in adult NHE8^−/−, NHE3^−/−, and NHE3^−/−/NHE8^−/− mice

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Ontogeny of Na+/H+ Antiporter Activity in Rat Proximal Convoluted Tubules

Cited by 43 publications

References 33 publications

Developmental Changes in Proximal Tubule Tight Junction Proteins

Developmental Changes in Proximal Tubule Tight Junction Proteins

Maturation of the Na+/H+antiporter (NHE3) in the proximal tubule of the hypothyroid adrenalectomized rat

Proximal tubule Na+/H+ exchanger activity in adult NHE8−/−, NHE3−/−, and NHE3−/−/NHE8−/− mice

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Maturation of the Na⁺/H⁺antiporter (NHE3) in the proximal tubule of the hypothyroid adrenalectomized rat

Proximal tubule Na⁺/H⁺ exchanger activity in adult NHE8^−/−, NHE3^−/−, and NHE3^−/−/NHE8^−/− mice