Chloride transport and intracellular chloride activity in the presence of theophylline in Amphiuma small intestine.

Abstract

SUMMARY1. Simultaneous bidirectional tracer fluxes of 22Na and 36C1 were measured under short-circuited conditions in isolated stripped segments of Amphiuma duodenum incubated in media containing Cl-and HCO3-.2. Theophylline (10 mM) increased the short-circuit current (IC), eliminated net Clabsorption and elevated the residual flux by more than 50 %.3. Subsequent addition of acetazolamide lowered the I., and reduced the residual flux.4. Using double-barrelled Cl--specific micro-electrodes the intracellular activity of Cl-averaged 2741 mm in the presence of theophylline, consistent with active accumulation of Cl-.5. Theophylline depolarized the mucosal membrane of villus epithelial cells by an average of 6-9 mV.6. These findings indicate that the inhibition ofCl-absorption by theophylline does not result from complete inhibition of mucosal Cl-uptake and provide evidence that HC03-secretion is enhanced by theophylline.

The effect of theophylline on intestinal bicarbonate transport measured by pH stat in Amphiuma.

“…In contrast the ISC was rapidly increased before declining to a stable value. (The polarity of 'sC is not serosa negative as in the previous manuscript (White, 1981) due to the absence of mucosal HC03-.) Identical results from eight tissues are averaged in Table 1.…”

“…Adult Amphiuma were stored and anaesthetized as described in the previous publication (White, 1981). Segments of proximal small intestine were stripped of their outer muscle layers opened and mounted as a sheet in a Plexiglas chamber that allowed measurement of the rate of HCO3-transport while the tissue was voltage clamped to eliminate the transepithelial electrical potential.…”

“…These effects are moderated by pre-exposure to acetazolamide. Further indirect evidence for simultaneous inhibition of Cl-absorption is also presented (White, 1981).…”

“…In the previous paper it was also shown that theophylline stimulated the residual flux in Cl--containing media as well (White, 1981).…”

Bicarbonate transport across the frog choroid plexus and its control by cyclic nucleotides.

“…production (see Davson, 1967). The major driving force for fluid secretion is active Na transport, which is brought about by an electrogenic Na/K exchange pump which is located in the brush-border membrane of the choroidal epithelium (Wright, 1972;Quinton, Wright & Tormey, 1973;Zeuthen & Wright, 1978, 1981Saito & Wright, 1982;Smith & Johanson, 1980;Masuzawa, Saito & Sato, 1980). Although much is known about the mechanism of Na secretion, little is known about its regulation.…”