Volume 91, Issue 2, February (2004), pp. 183-189 © The Author 2004
doi:10.1079/BJN20031045

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The relationships between potassium intakes, transmural potential difference of the rumen epithelium and magnesium absorption in wethers

S. Jittakhot¹, J. Th. Schonewille¹, H. S. Wouterse¹, C. Yuangklang¹, A. C. Beynen^1
1Department of Nutrition, Faculty of Veterinary Medicine, Utrecht University, P. O. Box 80.152, 3508 TD , Utrecht, The Netherlands

 (Received 21 May 2003–Revised 6 October 2003–Accepted 15 October 2003)

In vitro studies with isolated sheep rumen epithelium have shown that an increase in the lumen K concentration induces an increase in the transmural potential difference across the rumen epithelium (serosal side: positive), which is associated with a decrease in Mg transport. However, at lumen K concentrations >80 mmol/l, Mg transport across the epithelium became independent of the lumen K concentration. The present study was carried out to determine whether this observation also occurs in vivo. Four ruminally fistulated wethers were fed four rations supplemented with KHCO₃ (15·7, 37·6, 59·4 or 77·4 g K/kg DM) in a 4×4 Latin square design. Increased K intakes significantly increased the rumen K concentration. For all data combined, Mg absorption expressed as % intake was negatively correlated with the rumen K concentration. However, apparent Mg absorption either expressed in absolute terms (g/d) or as % intake was not significantly affected when the dietary K concentration was increased from 59·4 to 77·4 g/kg DM. Rumen K concentration was inversely correlated with the transmural potential difference (blood side: positive) (Pearson's r −0·709; R²_adj 0·468, P=0·002, n 16). It is concluded that in wethers apparent Mg absorption becomes independent of the dietary K concentration when the K concentration is >60 g/kg DM or equivalent to a postprandial rumen K concentration of about 125 mmol/l.

Keywords:
Magnesium absorption, Potassium intake, Transmural potential difference, Sheep

Abbreviations:
PDa, apical membrane potential, PDt, transmural potential difference