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Renal Na+/H+ exchanger isoforms and their regulation by thyroid hormone
K K Azuma1, D F Balkovetz, C E Magyar
1Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033, USA.
The American Journal of Physiology
|February 1, 1996
Summary
Thyroid status influences sodium-hydrogen exchange (NHE) in rat kidneys. NHE3 mRNA is most abundant and increases with hyperthyroidism, but protein levels remain unchanged, suggesting altered synthesis and turnover.
Area of Science:
- Nephrology
- Molecular Biology
- Endocrinology
Background:
- Sodium-hydrogen exchange (NHE) is crucial for proximal tubule function.
- NHE activity is modulated by thyroid hormone status.
- Multiple NHE isoforms exist, with four cloned cDNAs identified.
Purpose of the Study:
- To identify NHE mRNA isoforms in rat proximal tubules.
- To quantify the relative abundance of NHE mRNAs in the renal cortex.
- To investigate the impact of thyroid status on NHE mRNA and protein expression.
Main Methods:
- Blot hybridization of poly(A)+ RNA to detect NHE isoform mRNAs.
- Quantitative analysis of mRNA abundance in renal cortex.
- Immunoblotting to measure NHE3 protein levels.
- Sorbitol gradient analysis to determine protein localization.
Main Results:
- All four NHE isoform mRNAs (NHE1, -2, -3, -4) were detected in rat renal cortex.
- NHE1, -2, and -3 mRNAs were found in proximal tubules.
- NHE3 mRNA was fourfold more abundant than other isoforms in the renal cortex.
- NHE2 and NHE3 mRNA levels increased 1.5-fold from hypo- to hyperthyroidism.
- NHE3 protein was localized to the brush border, but its abundance did not change with thyroid status.
Conclusions:
- NHE3 is the predominant NHE isoform mRNA in the renal cortex and is located in apical membranes.
- Thyroid hormone treatment increases NHE3 mRNA but not protein levels.
- These findings suggest thyroid hormone influences NHE3 synthesis and turnover rates.