cAMP inhibition of murine intestinal Na/H exchange requires CFTR-mediated cell shrinkage of villus epithelium.
OBJECTIVE
Unlike the intestine of normal subjects, small-intestinal epithelia of cystic fibrosis patients and cystic fibrosis transmembrane conductance regulator protein-null (CFTR(-)) mice do not respond to stimulation of intracellular cyclic adenosine monophosphate with inhibition of electroneutral NaCl absorption. Because CFTR-mediated anion secretion has been associated with changes in crypt cell volume, we hypothesized that CFTR-mediated cell volume reduction in villus epithelium is required for intracellular cyclic adenosine monophosphate inhibition of Na(+)/H(+) exchanger (primarily Na(+)/H(+) exchanger 3) activity in the proximal small intestine.


METHODS
Transepithelial (22)Na flux across the jejuna of CFTR(+), CFTR(-), the basolateral membrane Na(+)/K(+)/2Cl(-) co-transporter protein NKCC1(+), and NKCC1(-) mice were correlated with changes in epithelial cell volume of the midvillus region.


RESULTS
Stimulation of intracellular cyclic adenosine monophosphate resulted in cessation of Na(+)/H(+) exchanger-mediated Na(+) absorption (J(ms)(NHE)) in CFTR(+) jejunum but had no effect on J(ms)(NHE) across CFTR(-) jejunum. Cell volume indices indicated an approximately 30% volume reduction of villus epithelial cells in CFTR(+) jejunum but no changes in CFTR(-) epithelium after intracellular cyclic adenosine monophosphate stimulation. In contrast, cell shrinkage induced by hypertonic medium inhibited J(ms)(NHE) in both CFTR(+) and CFTR(-) mice. Bumetanide treatment to inhibit Cl(-) secretion by blockade of the Na(+)/K(+)/2Cl(-) co-transporter, NKCC1, of stimulated CFTR(+) jejunum prevented maximal volume reduction of villus epithelium and recovered approximately 40% of J(ms)(NHE). Likewise, J(ms)(NHE) and cell volume were unaffected by intracellular cyclic adenosine monophosphate stimulation in NKCC1(-) jejuna.


CONCLUSIONS
These findings show a previously unrecognized role of functional CFTR expressed in villus epithelium: regulation of Na(+)/H(+) exchanger 3-mediated Na(+) absorption by alteration of epithelial cell volume.
D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D006982:Hypertonic Solutions / Q000494:pharmacology; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism; D007583:Jejunum / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D018181:Mice, Inbred CFTR; D018345:Mice, Knockout; D012964:Sodium / Q000378:metabolism; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D028021:Sodium-Potassium-Chloride Symporters / Q000235:genetics / Q000378:metabolism; D064506:Solute Carrier Family 12, Member 2
D006982:Hypertonic Solutions; C578878:Slc12a2 protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012964:Sodium; D000242:Cyclic AMP