Regulatory role of cAMP in transport of Na+, Cl- and short-chain fatty acids across sheep ruminal epithelium.
Sodium is absorbed in considerable amounts across the ruminal epithelium, whilst its transport is strongly interrelated with the permeation of chloride and short-chain fatty acids (SCFAs). However, regulation of ruminal Na+, Cl-, and SCFA absorption is hardly understood. The present study was therefore performed to characterize the influence of cAMP on sodium and sodium-coupled transport mechanisms in short-circuited, stripped ruminal epithelia of sheep. Elevation of intracellular cAMP concentrations by theophylline (10 mM) or theophylline in combination with forskolin (0.1 mM) significantly reduced mucosal-to-serosal sodium transport, leading to a reduction of net transport. The theophylline- or theophylline-forskolin-induced reduction of sodium transport was accompanied by a decrease in chloride net transport but revealed no effect on propionate flux. Short-chain fatty acids stimulated Na+ transport but their stimulatory effect was almost completely blocked by theophylline-forskolin. In solutions with and without SCFAs, the inhibitory effect of 1 mM amiloride on sodium transport was strongly reduced after theophylline-forskolin pretreatment of the tissues. Blocking the production of endogenous prostaglandins by addition of indomethacin (10 microM) led to a theophylline-sensitive stimulation of unidirectional and net fluxes of sodium. The findings indicate that apical, amiloride-sensitive Na+-H+ exchange and/or basolateral Na+-K+-ATPase can effectively be blocked by cAMP, leading to a decrease in sodium and chloride transport. In the ruminal epithelium, cAMP is a second messenger of prostaglandins, which are released spontaneously under in vitro conditions.
Gäbel
G
G
Department of Veterinary Physiology, University of Leipzig, Semmelweisstrasse 2, D-04103 Leipzig, Germany. gaebel@rz.uni-leipzig.de
Butter
H
H
Martens
H
H
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002021:Buffers; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D004594:Electrophysiology; D004848:Epithelium / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D066298:In Vitro Techniques; D008353:Mannitol / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011453:Prostaglandins / Q000494:pharmacology; D012417:Rumen / Q000187:drug effects / Q000378:metabolism*; D012756:Sheep; D012964:Sodium / Q000378:metabolism*; D013806:Theophylline / Q000494:pharmacology
D002021:Buffers; D002712:Chlorides; D005227:Fatty Acids; D010726:Phosphodiesterase Inhibitors; D011453:Prostaglandins; D005576:Colforsin; D008353:Mannitol; D012964:Sodium; D013806:Theophylline; D000242:Cyclic AMP