Cellular-mediated and diffusive magnesium transport across the descending colon of the rat

Gastroenterology
U Karbach

Abstract

Concentration and voltage dependence of unidirectional magnesium fluxes across the rat descending colon were measured in a modified Ussing-chamber. Mucosa to serosa (ms) magnesium flux exhibits a saturable component, whereas serosa to mucosa (sm) flux is linearly related to the magnesium concentration from 0.125 to 8 mmol/L. At all the concentrations used, ms magnesium transport is higher than the flux in the opposite direction, resulting in net magnesium absorption. Only ms magnesium transport has a voltage-independent, i.e., cellular-mediated component. Magnesium flux from serosa to mucosa, however, is totally voltage-dependent, i.e., purely diffusive and probably constrained to the paracellular pathway. The cellular-mediated fraction of ms magnesium transport is comparable to that found for calcium. Calcium (5 mmol/L) has no influence on ms flux or on the magnesium flux in the opposite direction. Magnesium (5 mmol/L) has no influence on the sm calcium flux but abolishes calcium absorption by decreasing ms calcium flux. The voltage clamp experiments reveal that magnesium has no influence on the cellular-mediated ms calcium transport but exclusively decreases diffusive calcium flux in this direction. Pretreatment with 1 alpha,...Continue Reading

Citations

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