Ion transport across the isolated intestinal mucosa of the winter flounder,Pseudopleuronectes americanus: II. Effects of cyclic AMP

Abstract

Addition of cyclic AMP and theophylline to the intestinal mucosa of the winter flounder, Pseudopleuronectes americanus decreased short-circuit current and net Na and Cl absorption and increased total conductance and the serosa-to-mucosa unidirectional Cl flux (JsmCl). The last two changes were independent of the original rate of NaCl absorption and persisted even when net absorption of Na and Cl had been abolished by ouabain. Voltage clamp experiments revealed that the increment in JsmCl produced by cyclic AMP is PD-insensitive and therefore not due to an increase in the Cl conductance of the paracellular shunt. Cyclic AMP appears, therefore, both to inhibit net NaCl absorption and to increase the Cl permeability and total conductance of the intestinal epithelial cells; its failure to stimulate secretion (in contrast to its action on mammalian intestine) may be related to the absence of crypts in flounder intestinal epithelium.

The role of leucocytes in the induction of fluid secretion by Salmonella typhimurium

“…It is, therefore, possible that the reduction of villus height and other morphological changes are a direct consequence of N2M affecting crypt cell mitoses. This would affect normal epithelial cell replacement and hence height of villi, and also crypt functions which by general consensus (Roggin et al, 1972;Field et-al., 1980;Welsh et al, 1982) are involved in normal secretion. Increased rates of villus base/crypt cell division are involved in the hypersecretory phase of rotavirus diarrhoea (Collins et al, 1988;Spencer et al, in press) and have been implicated in other bacterial toxin-induced diarrhoeas (Stephen and Osborne, 1988).…”

High rates of HCO3– secretion and Cl– absorption against adverse gradients in the marine teleost intestine: the involvement of an electrogenic anion exchanger and H+-pump metabolon?

“…The inward-directed electrochemical Na + gradient facilitates Na + uptake across the apical membrane, which is generally ascribed to two parallel co-transport systems: the absorptive Na + :K + :2Cl -cotransporter (NKCC2 in the following) and the Na + :Cl -cotransporter (NC in the following) (Field et al, 1980;Frizzell et al, 1979;Halm et al, 1985;Musch et al, 1982;Cutler and Cramb, 2002). The coupling of Na + uptake to the uptake of K + and Cl -is not necessary for Na + from a thermodynamical perspective because the electrochemical gradient for Na + is inwardly directed.…”

Modulation of NaCl absorption by [HCO3−] in the marine teleost intestine is mediated by soluble adenylyl cyclase

“…Reducing the saline's [HCO 3 Ϫ ] from 20 mM to 5 mM induces an ϳ60% reduction of Cl Ϫ absorption and I sc , a 30% reduction of Na ϩ absorption, and a significant increase in G te (12,13). HCO 3 Ϫ stimulation of ion absorption has been attributed to increases in pH (12), which stimulates NaCl and water absorption on its own (44).…”

“…Some studies have applied 8-Br-cAMP in combination with theophylline, and they have found robust inhibition of I sc and Na ϩ and Cl Ϫ absorption (13,15). However, theophylline is a nonspecific phosphodiesterase inhibitor that prevents both cAMP and cGMP degradation.…”