EFFECT OF TRANSMURAL POTENTIAL DIFFERENCE ON MG TRANSPORT ACROSS RUMEN EPITHELIUM FROM 4 DIFFERENT BREEDS OF SHEEP

Increasing the dietary intake of K reduces the Mg absorption from the forestomachs of ruminants by decreasing the apical membrane potential and increasing the transepithelial potential difference (V-t). To eval uate genetic variations in the dependence of Mg absorption on K intake , we performed Ussing chamber experiments and studied the effect of V- t on Mg-28 fluxes across rumen epithelium from different breeds of she ep. All breeds showed net absorption of Mg (J(net)(Mg)) in the absence of electrochemical gradients. J(net)(Mg) of Skudde was lower compared to Merino or Schwarzkopf sheep. Increasing V-t decreased mucosal to s erosal Mg flux (J(ms)(Mg)) and increased serosal to mucosal Mg flux. T he effect of V-t on J(net)(Mg) was almost identical in all breeds of s heep ( -30 to -45 % for a 25 mV increase in V-t). The effect of V-t on J(ms)(Mg) revealed a V-t-dependent and a V-t-independent component of transcellular Mg absorption in all breeds. Considering the driving fo rces for these two Mg transport mechanisms, the effect of K on Mg abso rption will mainly depend on the feeding regimen, i.e. dietary K must have a relatively higher effect on Mg absorption at low Mg intake leve ls, which explains the correlation between pasture quality and tetany frequency as well as the missing effect of K on Mg status in some olde r studies.