Influence of Theophylline on the Electrical Potential Difference and Ion Fluxes (Na, Cl, K) across the Isolated Rumen Epithelium of Sheep

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Abstract
Although it is well established that Na and Cl are actively absorbed by the rumen epithelium, nothing is known about the regulation of electrolyte transport across the rumen mucosa. Therefore, we have investigated the influence of theophylline, a known inhibitor of the enzyme phosphodiesterase, on the electrical parameters of the rumen epithelium as well as on electrolyte (Na, Cl, K) transport across this tissue. The experiments were performed using isolated rumen mucosa from sheep mounted in a Ussing type chamber. Serosal addition of theophylline resulted in a significant drop of the transepithelial potential difference as well as the short circuit current. The effect of theophylline is probably mediated by cAMP, since the addition of cAMP yielded qualitatively similar results. With respect to the ion fluxes only transport of Na in the mucoserosal direction and as a result the net flux of Na were significantly reduced in the presence of theophylline. The effects of theophylline on rumen epithelium are best explained by an inhibition of electrogenic as well as electroneutral Na transport. Since cAMP serves as a second messenger for the effect of various regulatory substances including gastrointestinal hormones and transmitters regulation of electrolyte transport across the rumen epithelium possibly occurs under physiological conditions.

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