Intestinal NaCl transport in NHE2 and NHE3 knockout mice.
Sodium/proton exchangers [Na(+)/H(+) (NHEs)] play an important role in salt and water absorption from the intestinal tract. To investigate the contribution of the apical membrane NHEs, NHE2 and NHE3, to electroneutral NaCl absorption, we measured radioisotopic Na(+) and Cl(-) flux across isolated jejuna from wild-type [NHE(+)], NHE2 knockout [NHE2(-)], and NHE3 knockout [NHE3(-)] mice. Under basal conditions, NHE(+) and NHE2(-) jejuna had similar rates of net Na(+) (approximately 6 microeq/cm(2) x h) and Cl(-) (approximately 3 microeq/cm(2) x h) absorption. In contrast, NHE3(-) jejuna had reduced net Na(+) absorption (approximately 2 microeq/cm(2) x h) but absorbed Cl(-) at rates similar to NHE(+) and NHE2(-) jejuna. Treatment with 100 microM 5-(N-ethyl-N-isopropyl) amiloride (EIPA) completely inhibited net Na(+) and Cl(-) absorption in all genotypes. Studies of the Na(+) absorptive flux (J) indicated that J in NHE(+) jejunum was not sensitive to 1 microM EIPA, whereas J in NHE3(-) jejunum was equally sensitive to 1 and 100 microM EIPA. Treatment with forskolin/IBMX to increase intracellular cAMP (cAMP(i)) abolished net NaCl absorption and stimulated electrogenic Cl(-) secretion in all three genotypes. Quantitative RT-PCR of epithelia from NHE2(-) and NHE3(-) jejuna did not reveal differences in mRNA expression of NHE3 and NHE2, respectively, when compared with jejunal epithelia from NHE(+) siblings. We conclude that 1) NHE3 is the dominant NHE involved in small intestinal Na(+) absorption; 2) an amiloride-sensitive Na(+) transporter partially compensates for Na(+) absorption in NHE3(-) jejunum; 3) cAMP(i) stimulation abolishes net Na(+) absorption in NHE(+), NHE2(-), and NHE3(-) jejunum; and 4) electroneutral Cl(-) absorption is not directly dependent on either NHE2 or NHE3.
Gawenis
Lara R
LR
Dalton Cardiovascular Research Center and Department of Biomedical Sciences, University of Missouri-Columbia, Columbia, Missouri 65211, USA.
Stien
Xavier
X
Shull
Gary E
GE
Schultheis
Patrick J
PJ
Woo
Alison L
AL
Walker
Nancy M
NM
Clarke
Lane L
LL
D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002713:Chlorine / Q000493:pharmacokinetics; D000242:Cyclic AMP / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology; D007583:Jejunum / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D011868:Radioisotopes / Q000493:pharmacokinetics; D012965:Sodium Chloride / Q000493:pharmacokinetics*; D012979:Sodium Radioisotopes / Q000493:pharmacokinetics; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism
D000889:Anti-Arrhythmia Agents; D011868:Radioisotopes; C513111:Slc9a2 protein, mouse; C000613386:Slc9a3 protein, mouse; D012979:Sodium Radioisotopes; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012965:Sodium Chloride; D002713:Chlorine; D000584:Amiloride; D000242:Cyclic AMP; C039614:ethylisopropylamiloride