Na+/H+-exchanger 3 activity and its gene in the spontaneously hypertensive rat kidney.
OBJECTIVE
To examine the mechanisms affecting proximal tubule sodium reabsorption, we studied the gene expression and functional changes of the Na+/H+-exchanger 3 (NHE3) and its gene expression in spontaneously hypertensive rats (SHR).


METHODS
The S1 segment of the superficial proximal convoluted tubules (PCT) was microdissected from collagenase-treated kidneys of SHR and Wistar-Kyoto (WKY) rats. The tubules were then superfused in a HEPES-buffered solution. The intracellular pH was measured by monitoring changes in fluorescent dye emission. By measuring the amiloride-sensitive intracellular pH recovery rate after intracellular acid loading with NH4Cl, we estimated the NHE3 activity. Northern blotting was performed to quantitate the NHE3 messenger RNA (mRNA) expression, and the NHE3 complementary DNA sequence was determined both in SHR and in WKY rat strains.


RESULTS
NHE3 activity was significantly higher in SHR than it was in WKY rats both at age 4 weeks and at age 7 weeks. Northern blot analysis showed that the mRNA expression did not differ significantly in the two strains at either age. Sequence analysis of complementary DNA of SHR NHE3 revealed five allelic variations compared with the known wild-type sequence in Sprague-Dawley rats. The same variations were also identified in the WKY rats.


CONCLUSIONS
NHE3 activity is increased in SHR compared with WKY rats of the same age. Changes in the NHE3 mRNA expression level and protein structure are not responsible for this difference between SHR and WKY rat strains.
Hayashi
M
M
Department of Internal Medicine, School of Medicine, Keio University, Japan.
Yoshida
T
T
Monkawa
T
T
Yamaji
Y
Y
Sato
S
S
Saruta
T
T
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D006973:Hypertension / Q000235:genetics* / Q000378:metabolism*; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008297:Male; D010477:Perfusion; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism*; D013045:Species Specificity
D017931:DNA Primers; D018076:DNA, Complementary; D012333:RNA, Messenger; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers