Heat-stable enterotoxin of Escherichia coli stimulates a non-CFTR-mediated duodenal bicarbonate secretory pathway.
The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) is an important pathway for duodenal mucosal bicarbonate secretion. Duodenal biopsies from CF patients secrete bicarbonate in response to heat-stable enterotoxin from Escherichia coli (STa) but not cAMP. To explore the mechanism of STa-induced bicarbonate secretion in CF more fully, we examined the role of CFTR in STa-stimulated duodenal bicarbonate secretion in mice. In vivo, the duodenum of CFTR (-/-) or control mice was perfused with forskolin (10(-4) M), STa (10(-7) M), uroguanylin (10(-7) M), 8-bromoguanosine 3',5'-cGMP (8-Br-cGMP) (10(-3) M), genistein (10(-6) M) plus STa, or herbimycin A (10(-6) M) plus STa. In vitro, duodenal mucosae were voltage-clamped in Ussing chambers, and bicarbonate secretion was measured by pH-stat. The effect of genistein, DIDS (10(-4) M), and chloride removal was also studied in vitro. Control, but not CF, mice produced a significant increase in duodenal bicarbonate secretion after perfusion with forskolin, uroguanylin, or 8-Br-cGMP. However, both control and CF animals responded to STa with significant increases in bicarbonate output. Genistein and herbimycin A abolished this response in CF mice but not in controls. In vitro, STa-stimulated bicarbonate secretion in CF tissues was inhibited by genistein, DIDS, and chloride-free conditions, whereas bicarbonate secretion persisted in control mice. In the CF duodenum, STa can stimulate bicarbonate secretion via tyrosine kinase activity resulting in apical Cl(-)/HCO(3)(-) exchange. Further studies elucidating the intracellular mechanisms responsible for such non-CFTR mediated bicarbonate secretion may lead to important therapies for CF.
Sellers
Zachary M
ZM
Div. of Gastroenterology (8414 University of California San Diego Medical Center, 200 West Arbor Dr., San Diego, CA 92103-8414, USA.
Childs
Debbie
D
Chow
Jimmy Y C
JY
Smith
Anders J
AJ
Hogan
Daniel L
DL
Isenberg
Jon I
JI
Dong
Hui
H
Barrett
Kim E
KE
Pratha
Vijaya S
VS
D000818:Animals; D001427:Bacterial Toxins / Q000494:pharmacology*; D016227:Benzoquinones; D001639:Bicarbonates / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D003550:Cystic Fibrosis / Q000378:metabolism*; D004386:Duodenum / Q000378:metabolism*; D004768:Enterotoxins / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D029968:Escherichia coli Proteins; D019833:Genistein / Q000494:pharmacology; D066298:In Vitro Techniques; D047029:Lactams, Macrocyclic; D051379:Mice; D045265:Natriuretic Peptides; D010455:Peptides / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011809:Quinones / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives
D001427:Bacterial Toxins; D016227:Benzoquinones; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D004768:Enterotoxins; D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D047029:Lactams, Macrocyclic; D045265:Natriuretic Peptides; D010455:Peptides; D011809:Quinones; C034151:heat stable toxin (E coli); C084362:uroguanylin; D005576:Colforsin; D017828:Rifabutin; C016276:8-bromocyclic GMP; C020754:herbimycin; D019833:Genistein; D011505:Protein-Tyrosine Kinases; D006152:Cyclic GMP