Sodium, hydrogen antiporter activation by extracellular adenosine triphosphate in biliary epithelial cells.
OBJECTIVE
Extracellular nucleotides are secretagogues and influence ion permeability. The aim of this study was to investigate whether secretagogues activate transmembrane acid-base carriers, e.g., sodium, hydrogen antiporter in cholangiocytes.


METHODS
Cells were loaded with pH and Ca(2+)-sensitive dyes. Intracellular changes in ion concentrations were monitored by confocal laser scanning microscopy. Adenosine 3', 5'-cyclic monophosphate was determined by standard methods.


RESULTS
Baseline intracellular pH (pH1) averaged 7.28 +/- 0.17 pH units. Adenosine triphosphate (ATP; 10 mumol/L) increased baseline pH1 by 0.28 +/- 0.06 pH units/10 min (P < 0.01). Ten and 100 mumol/L ATP increased Na+, H+ antiporter-mediated proton flux from 9.4 +/- 4.9 mmol. L-1 min-1 to 17.2 +/- 11.8 and 16.7 +/- 10.3 mmol. L(-1)-min(-1) (P < 0.001), respectively. Under control and ATP-stimulated conditions, 1 mmol/L amiloride blocked pH1 recovery, indicating true activation of Na+, H+ antiporter by extracellular ATP. Inhibition of basolateral Na+, H+ antiporter isoform inhibited stimulation by ATP. Na+, H+ antiporter-mediated proton flux was stimulated by adenosine, uridine triphosphate, adenosine-5'-0-(3-thiotriphosphate), alpha, beta-methylene-ATP, and 2-methylthio-ATP but not prevented by adenosine receptor blocking. Activation by ATP was not influenced by the Ca2+/protein kinase C/calmodulin system but could be mimicked by addition of N6,2'-O-dibutyryladenosine-3',5'-cyclic monophosphate and was inhibited by pertussis toxin.


CONCLUSIONS
Extracellular nucleotides may modulate secretory and absorptive function of cholangiocytes by activating Na+/H+ exchange mechanisms.
Department of Medicine, University of Heidelberg, Germany. christoph-elsing@krzmail.krz.uni-heidelberg.de
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Elsing
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Kassner
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Stremmel
D000241:Adenosine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000584:Amiloride / Q000494:pharmacology; D001652:Bile Ducts / Q000166:cytology / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000032:analysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D037342:Pertussis Toxin; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects*; D014544:Uridine Triphosphate / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D017923:Sodium-Hydrogen Exchangers; D010566:Virulence Factors, Bordetella; D003994:Bucladesine; D000584:Amiloride; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D037342:Pertussis Toxin; D000241:Adenosine; D002118:Calcium; D014544:Uridine Triphosphate