Divalent cations reduce the electrogenic transport of monovalent cations across rumen epithelium.
The rumen epithelium of sheep and goats showed an increase in short circuit current ( Isc) and transepithelial conductance (gt) upon mucosal removal of divalent cations. A divalent-sensitive Isc and gt were present in Na+, K+ or Rb+ buffer, but nearly abolished in mucosal NMDG+ (N-methyl-D-glucamine) buffer. High K buffer, addition of BaCl2 or of ouabain on the serosal side also reduced or abolished the divalent-sensitive Isc. Mucosal Ca2+ was more potent in blocking Isc, but had the same potency as Mg2+ in blocking gt. A prolonged mucosal deprivation of Mg2+ ions increased gt, potential difference and basal as well as the Ca2+-sensitive Isc. Mucosal addition of Mg2+ had a smaller effect on gt after serosal preincubation with Ba. The data suggest that rumen epithelial cells exhibit an apical non-selective cation conductance, which permits the passage of monovalents in the mucosal absence of divalents. The development of a divalent-sensitive Isc in Na buffer requires Na+/K+ pumps and K+ recycling through Ba2+-sensitive K+ conductances on the basolateral side. This Isc is blocked by extracellular Ca2+ and both extracellular and intracellular Mg2+ ions. A prolonged deprivation of mucosal Mg2+ alone seems to affect intracellular Mg2+ in this Mg2+-absorbing tissue.
D000818:Animals; D017609:Barium Compounds / Q000494:pharmacology; D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology*; D002414:Cations, Monovalent / Q000493:pharmacokinetics*; D002712:Chlorides / Q000494:pharmacology; D004553:Electric Conductivity; D004848:Epithelium / Q000378:metabolism; D006041:Goats; D015759:Ionomycin / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D008275:Magnesium Deficiency / Q000378:metabolism; D009092:Mucous Membrane / Q000187:drug effects / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D012417:Rumen / Q000378:metabolism*; D012704:Serous Membrane / Q000187:drug effects; D012756:Sheep
D017609:Barium Compounds; D002413:Cations, Divalent; D002414:Cations, Monovalent; D002712:Chlorides; C024986:barium chloride; D015759:Ionomycin; D010042:Ouabain; D008274:Magnesium; D002118:Calcium