title: The effect of potassium and the transmural potential difference on magnesium transport across an isolated preparation of sheep rumen epithelium.
abstract: Isolated mucosal sheets of sheep rumen were studied in vitro in Ussing chambers using a computer-controlled voltage clamp. Undirectional Mg2+ fluxes were measured at high (70 mmol X l-1) or low (5 mmol X 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 Mg2+ fluxes were 52.2 +/- 6.5 nmol X cm-2 X h-1 from the mucosal to serosal side, JMgms, and 11.6 +/- 1.4 nmol X cm-2 X h-1 from the serosal to mucosal side, JMgsm. The net flux, JMgnet, was 40.6 +/- 5.9 nmol X cm-2 X 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: JMgms, 76.1 +/- 8.3; JMgsm, 8.0 +/- 1.4; and JMgnet 68.1 +/- 7.7 nmol X cm-2 X h-1. The results of the low (control) and high mucosal K+ group did not differ significantly when Mg2+ fluxes were measured under short-circuit conditions: JMgms, 72.1 +/- 8.7; JMgsm, 6.5 +/- 2.6; and JMgnet, 65.5 +/- 9.0 nmol X cm-2 X 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: JMgms, 47.4 +/- 3.0; JMgsm, 12.3 +/- 2.3; and JMgnet, 35.2 +/- 4.1 nmol X cm-2 X h-1.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D004594:Electrophysiology; D004848:Epithelium / Q000502:physiology; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D012417:Rumen / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*; D013997:Time Factors
chemical_list: D008274:Magnesium; D011188:Potassium