title: Acid increases NHE8 surface expression and activity in NRK cells.
abstract: We previously demonstrated that there is a paucity of brush-border membrane NHE3 in neonates, the predominant Na(+)/H(+) exchanger in the adult proximal tubule, while NHE8 is relatively highly expressed in neonates compared with adults. We recently showed that metabolic acidosis in neonatal rodents can increase brush-border membrane NHE8 protein expression and Na(+)/H(+) exchange activity. To further examine the regulation of NHE8 by acid, we incubated NRK cells, which express NHE8 but not NHE3, with either acid or control media (6.6 vs. 7.4). There was an increase in Na(+)/H(+) exchanger activity within 6 h of incubation with acid media assessed as the rate of sodium-dependent recovery of pH from an acid load (dpH(i)/dt). The acid stimulation persisted for at least 24 h. The increase in Na(+)/H(+) exchange activity was paralleled by an increase in surface expression of NHE8, assessed by surface biotinylation and streptavidin precipitation. The increase in both apical membrane NHE8 protein expression and Na(+)/H(+) exchange activity with pH 6.6 media compared with 7.4 media was not affected by actinomycin D or cycloheximide consistent with an increase in surface expression independent of mRNA or protein synthesis. Furthermore, there was no increase in total cellular NHE8 protein abundance or mRNA abundance with acid media. Finally, we demonstrate that the increase in surface expression of NHE8 with acid media was blocked by colchicine and cytochalasin D and mediated by acid increasing the rate of exocytosis. In conclusion, NHE8 surface expression and activity are regulated by acid media by increasing the rate of trafficking to the apical membrane.
authors.affiliation: Dept. of Pediatrics, U.T. Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9063, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Joseph
authors.forename: Katherine
authors.initials: K
authors.lastname: Twombley
authors.forename: Jyothsna
authors.initials: J
authors.lastname: Gattineni
authors.forename: Qiuyu
authors.initials: Q
authors.lastname: Zhang
authors.forename: Vangipuram
authors.initials: V
authors.lastname: Dwarakanath
authors.forename: Michel
authors.initials: M
authors.lastname: Baum
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism; D051381:Rats; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: C502388:Slc9a8 protein, rat; D017923:Sodium-Hydrogen Exchangers
references.citation: Am J Physiol Renal Physiol. 2005 Oct;289(4):F685-91
references.pmid: 15942046
references.citation: Am J Physiol Regul Integr Comp Physiol. 2007 Mar;292(3):R1230-5
references.pmid: 17095646
references.citation: Am J Physiol. 1982 May;242(5):F499-507
references.pmid: 6805335
references.citation: Pediatr Res. 2000 Aug;48(2):206-10
references.pmid: 10926296
references.citation: Am J Physiol Regul Integr Comp Physiol. 2010 Nov;299(5):R1360-8
references.pmid: 20720175
references.citation: Am J Physiol Renal Physiol. 2001 Jan;280(1):F34-42
references.pmid: 11133512
references.citation: Am J Physiol Renal Physiol. 2003 Mar;284(3):F467-73
references.pmid: 12409279
references.citation: Am J Physiol Cell Physiol. 2007 Jan;292(1):C396-404
references.pmid: 16971495
references.citation: Am J Physiol. 1996 Oct;271(4 Pt 2):F917-25
references.pmid: 8898023
references.citation: J Clin Invest. 2000 Apr;105(8):1141-6
references.pmid: 10772659
references.citation: Am J Physiol. 1995 Jul;269(1 Pt 1):C126-33
references.pmid: 7631739
references.citation: Am J Physiol Renal Physiol. 2007 Sep;293(3):F761-6
references.pmid: 17581925
references.citation: J Clin Invest. 1988 Oct;82(4):1445-53
references.pmid: 2844858
references.citation: Genome Biol. 2002 Jun 18;3(7):RESEARCH0034
references.pmid: 12184808
references.citation: Kidney Int. 1998 May;53(5):1254-8
references.pmid: 9573540
references.citation: J Clin Invest. 1991 Nov;88(5):1703-8
references.pmid: 1658050
references.citation: J Clin Invest. 1990 Feb;85(2):499-506
references.pmid: 2153709
references.citation: Am J Physiol Renal Physiol. 2007 Jul;293(1):F255-61
references.pmid: 17429030
references.citation: Am J Physiol. 1988 Dec;255(6 Pt 1):C844-56
references.pmid: 2849306
references.citation: Am J Physiol. 1984 Aug;247(2 Pt 2):F339-43
references.pmid: 6087681
references.citation: Am J Physiol Cell Physiol. 2000 Aug;279(2):C410-9
references.pmid: 10913008
references.citation: J Clin Invest. 1999 Feb;103(3):429-35
references.pmid: 9927505
references.citation: J Biol Chem. 1996 Dec 20;271(51):32749-52
references.pmid: 8955109
references.citation: Pediatr Res. 1992 Apr;31(4 Pt 1):411-4
references.pmid: 1315022
references.citation: Am J Physiol. 1993 Jun;264(6 Pt 2):F1027-31
references.pmid: 8391752
references.citation: Am J Physiol. 1991 Nov;261(5 Pt 2):F746-52
references.pmid: 1951707
references.citation: Am J Physiol Renal Physiol. 2008 Jan;294(1):F198-204
references.pmid: 17977906
references.citation: Am J Physiol. 1983 Sep;245(3):F382-90
references.pmid: 6311027