VIP, serotonin, and epinephrine modulate the ion selectivity of tight junctions of goldfish intestine.
Bidirectional fluxes of Cl- across isolated and stripped goldfish intestinal epithelium mounted in Ussing-type chambers increased after addition of 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP), suggesting an increase of the paracellular permeability for Cl-. Confirming this, the addition of 8-Br-cAMP to the stripped intestine reduced the diffusion potential generated by isosmotic serosal or mucosal replacement of part of the NaCl by mannitol. The addition of the protein kinase C (PKC) activator 4 beta-phorbol 12,13-dibutyrate (PDB), 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP), or the Ca2+ ionophore A23187 was without effect on the Cl- permeability. The cAMP-specific reduction of the diffusion potential was used to screen the epithelium for the presence of receptors coupled to adenylyl cyclase. The results indicate the presence of a serotonin (5-HT) receptor, positively coupled to adenylyl cyclase but insensitive to 5-HT1-, 5-HT2-, 5-HT3-, and nonclassical 5-HT4-receptor antagonists. Addition of vasoactive intestinal polypeptide (VIP) also reduced the diffusion potential in a dose-dependent way. Epinephrine restored the diffusion potential after its reduction by 5-HT or VIP. This effect could be mimicked by the partial alpha 2-adrenergic receptor agonist clonidine and blocked by the alpha 2-antagonists yohimbine and idazoxan. The Rp diastereoisomer of cAMP, (Rp)adenosine 3',5'-cyclic phosphorothioate [(Rp)cAMPS], counteracted the effect of VIP. The results indicate that in goldfish enterocytes VIP and 5-HT reduce the ion selectivity of the tight junctions through elevation of cAMP and that activation of alpha 2-adrenergic receptors antagonize these effects.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Experimental Zoology, University of Amsterdam, The Netherlands.
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Bakker
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Dekker
H R
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De Jonge
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JA
Groot
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology; D004837:Epinephrine / Q000494:pharmacology*; D006054:Goldfish; D007150:Immunohistochemistry; D007365:Intercellular Junctions / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D007477:Ions; D012701:Serotonin / Q000494:pharmacology*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology*
D007477:Ions; D015124:8-Bromo Cyclic Adenosine Monophosphate; C016276:8-bromocyclic GMP; D012701:Serotonin; D014660:Vasoactive Intestinal Peptide; D006152:Cyclic GMP; D004837:Epinephrine