Tissue-specific regulation of sodium/proton exchanger isoform 3 activity in Na(+)/H(+) exchanger regulatory factor 1 (NHERF1) null mice. cAMP inhibition is differentially dependent on NHERF1 and exchange protein directly activated by cAMP in ileum versus proximal tubule.
The multi-PDZ domain containing protein Na(+)/H(+) Exchanger Regulatory Factor 1 (NHERF1) binds to Na(+)/H(+) exchanger 3 (NHE3) and is associated with the brush border (BB) membrane of murine kidney and small intestine. Although studies in BB isolated from kidney cortex of wild type and NHERF1(-/-) mice have shown that NHERF1 is necessary for cAMP inhibition of NHE3 activity, a role of NHERF1 in NHE3 regulation in small intestine and in intact kidney has not been established. Here a method using multi-photon microscopy with the pH-sensitive dye SNARF-4F (carboxyseminaphthorhodafluors-4F) to measure BB NHE3 activity in intact murine tissue and use it to examine the role of NHERF1 in regulation of NHE3 activity. NHE3 activity in wild type and NHERF1(-/-) ileum and wild type kidney cortex were inhibited by cAMP, whereas the cAMP effect was abolished in kidney cortex of NHERF1(-/-) mice. cAMP inhibition of NHE3 activity in these two tissues is mediated by different mechanisms. In ileum, a protein kinase A (PKA)-dependent mechanism accounts for all cAMP inhibition of NHE3 activity since the PKA antagonist H-89 abolished the inhibitory effect of cAMP. In kidney, both PKA-dependent and non-PKA-dependent mechanisms were involved, with the latter reproduced by the effect on an EPAC (exchange protein directly activated by cAMP) agonist (8-(4-chlorophenylthio)-2'O-Me-cAMP). In contrast, the EPAC agonist had no effect in proximal tubules in NHERF1(-/-) mice. These data suggest that in proximal tubule, NHERF1 is required for all cAMP inhibition of NHE3, which occurs through both EPAC-dependent and PKA-dependent mechanisms; in contrast, cAMP inhibits ileal NHE3 only by a PKA-dependent pathway, which is independent of NHERF1 and EPAC.
Murtazina
Rakhilya
R
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Kovbasnjuk
Olga
O
Zachos
Nicholas C
NC
Li
Xuhang
X
Chen
Yueping
Y
Hubbard
Ann
A
Hogema
Boris M
BM
Steplock
Deborah
D
Seidler
Ursula
U
Hoque
Kazi M
KM
Tse
Chung Ming
CM
De Jonge
Hugo R
HR
Weinman
Edward J
EJ
Donowitz
M
M
D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000502:physiology; D007082:Ileum / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D020033:Protein Isoforms; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014018:Tissue Distribution
C482601:Epac protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D010750:Phosphoproteins; D020033:Protein Isoforms; C000613386:Slc9a3 protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C093376:sodium-hydrogen exchanger regulatory factor; D000242:Cyclic AMP