title: AE2 Cl-/HCO3- exchanger is required for normal cAMP-stimulated anion secretion in murine proximal colon.
abstract: Anion secretion by colonic epithelium is dependent on apical CFTR-mediated anion conductance and basolateral ion transport. In many tissues, the NKCC1 Na(+)-K(+)-2Cl(-) cotransporter mediates basolateral Cl(-) uptake. However, additional evidence suggests that the AE2 Cl(-)/HCO(3)(-) exchanger, when coupled with the NHE1 Na(+)/H(+) exchanger or a Na(+)-HCO(3)(-) cotransporter (NBC), contributes to HCO(3)(-) and/or Cl(-) uptake. To analyze the secretory functions of AE2 in proximal colon, short-circuit current (I(sc)) responses to cAMP and inhibitors of basolateral anion transporters were measured in muscle-stripped wild-type (WT) and AE2-null (AE2(-/-)) proximal colon. In physiological Ringer, the magnitude of cAMP-stimulated I(sc) was the same in WT and AE2(-/-) colon. However, the I(sc) response in AE2(-/-) colon exhibited increased sensitivity to the NKCC1 inhibitor bumetanide and decreased sensitivity to the distilbene derivative SITS (which inhibits AE2 and some NBCs), indicating that loss of AE2 results in a switch to increased NKCC1-supported anion secretion. Removal of HCO(3)(-) resulted in robust cAMP-stimulated I(sc) in both AE2(-/-) and WT colon that was largely mediated by NKCC1, whereas removal of Cl(-) resulted in sharply decreased cAMP-stimulated I(sc) in AE2(-/-) colon relative to WT controls. Inhibition of NHE1 had no effect on cAMP-stimulated I(sc) in AE2(-/-) colon but caused a switch to NKCC1-supported secretion in WT colon. Thus, in AE2(-/-) colon, Cl(-) secretion supported by basolateral NKCC1 is enhanced, whereas HCO(3)(-) secretion is diminished. These results show that AE2 is a component of the basolateral ion transport mechanisms that support anion secretion in the proximal colon.
authors.affiliation: Department of Physiology, University of Utah, Salt Lake City, Utah 84108, USA. Lara.Gawenis@hsc.utah.edu
authors.forename: Lara R
authors.initials: LR
authors.lastname: Gawenis
authors.forename: Emily M
authors.initials: EM
authors.lastname: Bradford
authors.forename: Seth L
authors.initials: SL
authors.lastname: Alper
authors.forename: Vikram
authors.initials: V
authors.lastname: Prasad
authors.forename: Gary E
authors.initials: GE
authors.lastname: Shull
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D027321:Anion Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000838:Anions / Q000378:metabolism*; D017920:Antiporters / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism; D002034:Bumetanide / Q000494:pharmacology; D024402:Carbonic Anhydrase II / Q000235:genetics / Q000378:metabolism; D024403:Carbonic Anhydrase III / Q000235:genetics / Q000378:metabolism; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000235:genetics / Q000378:metabolism; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D002432:Cecum / Q000473:pathology; D002712:Chlorides / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D003106:Colon / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D000242:Cyclic AMP / Q000502:physiology*; D055724:Electrophysiological Phenomena; D015870:Gene Expression / Q000235:genetics; D007473:Ion Channels / Q000235:genetics; D016623:Ion Pumps / Q000235:genetics; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D064606:SLC4A Proteins; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters / Q000187:drug effects / Q000378:metabolism; D064506:Solute Carrier Family 12, Member 2
chemical_list: D027321:Anion Transport Proteins; D000838:Anions; D017920:Antiporters; D001639:Bicarbonates; D002257:Carbonic Anhydrase Inhibitors; D027682:Cation Transport Proteins; D002712:Chlorides; D007473:Ion Channels; D016623:Ion Pumps; D064606:SLC4A Proteins; C578878:Slc12a2 protein, mouse; C062002:Slc4a3 protein, mouse; C490997:Slc9a1 protein, mouse; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D002034:Bumetanide; D005576:Colforsin; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D000242:Cyclic AMP; D024402:Carbonic Anhydrase II; D024403:Carbonic Anhydrase III; D002256:Carbonic Anhydrases; D000086:Acetazolamide; D015056:1-Methyl-3-isobutylxanthine; C039614:ethylisopropylamiloride