title: Quantitative contribution of NHE2 and NHE3 to rabbit ileal brush-border Na+/H+ exchange.
abstract: Intestinal neutral NaCl absorption, which is made up of brush-border (BB) Na+/H+ exchange linked to BB Cl-/HCO3- exchange, is up- and downregulated as part of digestion and diarrheal diseases. Glucocorticoids stimulate ileal NaCl absorption and BB Na+/H+ exchange. Intestinal BB contains two Na+/H+ exchanger isoforms, NHE2 and NHE3, but their relative roles in rabbit ileal BB Na+/H+ exchange has not been determined. A technique to separate the contribution of NHE2 and NHE3 to ileal BB Na+/H+ exchange activity was standardized by using an amiloride-related compound, HOE-694. Under basal conditions, both NHE2 and NHE3 contribute approximately 50% to ileal Na+/H+ exchange. Glucocorticoids (methylprednisolone) increase BB Na+/H+ exchange (2.5 times) but increase only ileal NHE3 activity (4.1 times), without an effect on NHE2 activity. Thus ileal BB Na+/H+ exchange in animals treated with glucocorticoids is 69% via NHE3. A quantitative Western analysis for NHE3 was developed, using as an internal standard a fusion protein of the COOH-terminal 85 amino acids of NHE3 and maltose binding protein. Glucocorticoid treatment increased the amount of BB NHE3. The quantitative Western analysis showed that NHE3 makes up 0.018% of ileal BB protein in control rabbits and 0.042% (2.3 times as much) in methylprednisolone-treated rabbits. Methylprednisolone treatment did not alter the amount of ileal BB NHE2 protein. NHE3 turnover number was estimated to be 458 cycles/s under basal conditions and 708 cycles/s in glucocorticoid-treated ileum. Thus methylprednisolone stimulates ileal BB Na+/H+ exchange activity only by an effect on NHE3 and not on NHE2; it does so primarily by increasing the amount of BB NHE3, although it also increases the NHE3 turnover number.
authors.affiliation: Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2195, USA.
authors.forename: L
authors.initials: L
authors.lastname: Wormmeester
authors.forename: F
authors.initials: F
authors.lastname: Sanchez de Medina
authors.forename: F
authors.initials: F
authors.lastname: Kokke
authors.forename: C M
authors.initials: CM
authors.lastname: Tse
authors.forename: S
authors.initials: S
authors.lastname: Khurana
authors.forename: J
authors.initials: J
authors.lastname: Bowser
authors.forename: M E
authors.initials: ME
authors.lastname: Cohen
authors.forename: M
authors.initials: M
authors.lastname: Donowitz
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005938:Glucocorticoids / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D008297:Male; D008775:Methylprednisolone / Q000494:pharmacology; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D011817:Rabbits; D016324:Sequence Tagged Sites; D012964:Sodium / Q000493:pharmacokinetics; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology
chemical_list: D005938:Glucocorticoids; D006146:Guanidines; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C074107:3-methylsulfonyl-4-piperidinobenzoyl guanidine; D012964:Sodium; D008775:Methylprednisolone