The presence of NHE1 and NHE3 Na+-H+ exchangers and an apical cAMP-independent Cl- channel indicate that both absorptive and secretory functions are present in calf gall bladder epithelium.
We investigated the transport systems that can sustain Na+ and Cl- movements across bovine gall bladder epithelium, focusing on the Na+-H+ exchanger (NHE) family and chloride conductive pathways. Experiments conducted using the fluorescent probe acridine orange (AO) with brush-border membrane vesicles (BBMV) or vesicles obtained from the total epithelium (EMV) demonstrated the presence of a Na+-H+ exchange in both preparations. The use of specific inhibitors indicated the presence of an apical NHE3 exchanger and a NHE1 isoform which should reside in the basolateral membrane. Using reverse transcriptase (RT) PCR, we identified cDNA fragments corresponding to the NHE1, NHE3, Cl--HCO3- (AE2a) transporters and to the CFTR channel. Using the patch-clamp technique, we investigated Cl- conductances on cultured epithelial cells. We found a 5 pS Cl- channel with a voltage-independent open probability, insensitive to stilbenes (SITS), Zn2+ and cAMP. The results suggest that absorption and secretion coexist in calf gall bladder epithelium. A Na+-H+-Cl--HCO3- double exchange may, at least partially, sustain the absorptive function, and a Cl- apical conductive pathway may be involved in secretion. The conductance we observed does not seem to be cAMP-regulated, unlike other mammalian gall bladders.
Bazzini
C
C
Department of General Physiology and Biochemistry, University of Milan, Via Celoria 26, 20133 Milan, Italy.
Bottà
G
G
Meyer
G
G
Baroni
M D
MD
Paulmichl
M
M
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000165:Acridine Orange / Q000378:metabolism; D000584:Amiloride / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D027321:Anion Transport Proteins; D017920:Antiporters; D001692:Biological Transport / Q000502:physiology; D002417:Cattle; D002458:Cell Fractionation; D002462:Cell Membrane / Q000378:metabolism*; D016764:Cell Polarity; D002478:Cells, Cultured; D018118:Chloride Channels / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004232:Diuretics / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000378:metabolism; D005704:Gallbladder / Q000378:metabolism*; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms; D064606:SLC4A Proteins; D016415:Sequence Alignment; D012964:Sodium / Q000378:metabolism; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology
D027321:Anion Transport Proteins; D017920:Antiporters; C505032:CFTR protein, human; D018118:Chloride Channels; D004232:Diuretics; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D008565:Membrane Proteins; D020033:Protein Isoforms; D064606:SLC4A Proteins; C000613385:SLC9A3 protein, human; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C069139:growth factor-activatable Na-H exchanger NHE-1; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium; D000242:Cyclic AMP; D000165:Acridine Orange; D015032:Zinc