Proximal tubule Na+/H+ exchanger activity in adult NHE8(-/-), NHE3(-/-), and NHE3(-/-)/NHE8(-/-) mice

1UT Southwestern Medical Center at Dallas.
AJP Renal Physiology (Impact Factor: 3.25). 10/2012; 303(11). DOI: 10.1152/ajprenal.00415.2012
Source: PubMed


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 if 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 brush border membranes 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 increase 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 to control mice. Compared to 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 to 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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    • "Functional analysis using isolated renal proximal tubules from NHE3/8 double-KO mice confirmed this view (Baum et al., 2012). Surprisingly, however, the acidosis of NHE3/8 double-KO mice was also mild and comparable to that in NHE3 KO mice (Baum et al., 2012). "
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    • "The protein obtained from brush border vesicle or total lysates were mixed with 5× loading buffer (2.5 mM Tris HCl [pH 6.8], 2.5% β-mercaptoethanol, 25% glycerol, and 2.5% SDS). The proteins were heated to 85°C for 5 min (NHE3) and 37°C for 5 min (NHE8) and then loaded on an 8% polyacrylamide gel and separated using SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) as has been described (Baum et al. 2012; Joseph et al. 2012). Proteins were then transferred to a polyvinylidene difluoride membrane (Immobilon; Millipore, Billerica, MA) at 400 mA for 1 h at 4°C (Baum et al. 1998; Shah et al. 2000; Bobulescu et al. 2005). "
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