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THE EFFECT OF POTASSIUM AND THE TRANSMURAL POTENTIAL DIFFERENCE ON MAGNESIUM TRANSPORT ACROSS AN ISOLATED PREPARATION OF SHEEP RUMEN EPITHELIUM
Author(s) -
Martens H.,
Gäbel G.,
Strozyk H.
Publication year - 1987
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0144-8757
DOI - 10.1113/expphysiol.1987.sp003062
Subject(s) - rumen , potassium , ussing chamber , magnesium , chemistry , zoology , clamp , flux (metallurgy) , voltage clamp , potential difference , medicine , analytical chemistry (journal) , endocrinology , in vitro , biology , biochemistry , chromatography , membrane potential , mechanical engineering , clamping , organic chemistry , fermentation , engineering , electrode
Isolated mucosal sheets of sheep rumen were studied in vitro in Ussing chambers using a computer‐controlled voltage clamp. Undirectional Mg 2+ fluxes were measured at high (70 mmol.l −1 ) or low (5 mmol.l −1 ) mucosal concentrations of K + under open‐ or voltage‐clamp conditions. A high mucosal concentration of K + caused a potential difference (p.d.) of 25·1 ± 1·8 mV, blood side positive. The Mg 2+ fluxes were 52·2 ± 6·5 nmol.cm −2 .h −1 from the mucosal to serosal side, J Mg ms , and 11·6 ± 1·4 nmol.cm −2 .h −1 from the serosal to mucosal side, J Mg sm . The net flux, J Mg net , was 40·6 ± 5·9 nmol.cm −2 .h −1 . When, at high mucosal K + concentrations the p.d. was abolished by an external current (short‐circuit conditions) significantly different flux data were obtained: J Mg ms , 76·1 ± 8·3; J Mg sm , 8·0 ± 1·4; and J Mg net 68·1 ± 7·7 nmol.cm −2 .h −1 . The results of the low (control) and high mucosal K + group did not differ significantly when Mg 2+ fluxes were measured under short‐circuit conditions: J Mg ms , 72·1 ± 8·7; J Mg sm , 6·5 ± 2·6; and J Mg net , 65·5 ± 9·0 nmol.cm −2 .h −1 . An increase of the p.d. to 26·6 ± 2·0 mV (control) by an external current led to significant alterations of the fluxes in the control group: J Mg ms , 47·4 ± 3·0; J Mg sm , 12·3 ± 2·3; and J Mg net , 35·2 ± 4·1 nmol.cm −2 .h −1 . Although it is suggested that an increased p.d. caused an enhanced passive flux of Mg 2+ from the serosal to the mucosal side through the shunt pathway, the magnitude of the decrease in J Mg ms cannot solely be explained by a reduction in the passive, putative paracellular part of J Mg ms .