title: cAMP-dependent secretagogues stimulate the NaHCO3cotransporter in the villous epithelium of the brushtail possum, Trichosurus vulpecula.
abstract: In the ileum of the brushtail possum, Trichosurus vulpecula, fluid secretion appears to be driven by electrogenic HCO3-secretion. Consistent with this, the cystic fibrosis transmembrane conductance regulator is expressed in the apical membrane of the ileal epithelial cells and the pancreatic or secretory variant of the NaHCO3cotransporter in the basolateral membrane. This suggests that in the possum ileum, electrogenic HCO3-secretion is driven by basolateral NaHCO3cotransporter (NBC) activity. To determine if the NBC contributes to HCO3-secretion in the possum ileum, intracellular pH (pHi) measurements in isolated villi were used to demonstrate NBC activity in the ileal epithelial cells and investigate the effect of cAMP-dependent secretagogues. In CO2/HCO3--free solutions, recovery of the epithelial cells from an acid load was Na+-dependent and ≈80% inhibited by ethyl-isopropyl-amiloride (EIPA, 10 µmol L-1), indicative of the presence of an Na+/H+exchanger, most likely NHE1. However, in the presence of CO2/HCO3-, EIPA only inhibited ≈ 50% of the recovery, the remainder was inhibited by 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS, 500 µmol L-1), indicative of NBC activity. Under steady-state conditions, NHE1 inhibition by EIPA had little effect on pHi in the presence or absence of secretagogues, but NBC inhibition with DIDS resulted in a rapid acidification of the cells, which was increased fivefold by secretagogues. These data demonstrate the functional activity of an NaHCO3cotransporter in the ileal epithelial cells. Furthermore, the stimulation of NBC activity by secretagogues is consistent with the involvement of an NaHCO3cotransporter in electrogenic HCO3-secretion.
authors.affiliation: Department of Physiology, School of Biomedical Sciences, University of Otago, PO Box 56, Dunedin, 9054, New Zealand.
authors.forename: Pin-Chun
authors.initials: PC
authors.lastname: Chao
authors.affiliation: Department of Physiology, School of Biomedical Sciences, University of Otago, PO Box 56, Dunedin, 9054, New Zealand. grant.butt@otago.ac.nz.
authors.forename: A Grant
authors.initials: AG
authors.lastname: Butt
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology*; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007082:Ileum / Q000187:drug effects* / Q000378:metabolism; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism; D007419:Intestinal Secretions / Q000378:metabolism*; D027982:Sodium-Bicarbonate Symporters / Q000819:agonists* / Q000378:metabolism; D000074082:Sodium-Hydrogen Exchanger 1 / Q000378:metabolism; D048330:Trichosurus / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D027982:Sodium-Bicarbonate Symporters; D000074082:Sodium-Hydrogen Exchanger 1; D005576:Colforsin; D000584:Amiloride; D000242:Cyclic AMP; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D015056:1-Methyl-3-isobutylxanthine; C039614:ethylisopropylamiloride
keywords: Brushtail possum; HCO3 secretion; Ileum; Marsupial; NaHCO3 cotransport; Trichosurus vulpecula