AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 2 362-R368, Copyright © 1993 by American Physiological Society

ARTICLES

VIP, serotonin, and epinephrine modulate the ion selectivity of tight junctions of goldfish intestine

R. Bakker, K. Dekker, H. R. De Jonge and J. A. Groot
Department of Experimental Zoology, University of Amsterdam, The Netherlands.

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)

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