Cellular adaptation of the mouse cortical thick ascending limb of Henle's loop (CTAL) to dietary magnesium restriction: enhanced transepithelial Mg2+and Ca2+ transport

Mice aged 4 or 8 weeks were fed with a low-Mg2+ diet for 1, 2, 3 or 4 days. After 1 day of diet, the urinary excretion of Mg2+ and Ca2+ was strongly r educed in both animal groups (4 and 8 weeks)? accompanied by a significant fall in plasma Mg2+ concentration and an increase in urinary volume. This p rofile persisted after 2, 3 or 4 days of dietary Mg'f restriction. After 1 day of diet, transepithelial ion net fluxes of Na+, Cl-, Ca2+ and Mg2+ (J(N a), J(Cl), J(Ca), J(Mg)) measured in vitro from isolated perfused cortical thick ascending limbs (CTALs) of these animals remained unchanged. After 2 days of diet, mea surements of Jc, and J(Mg) in isolated perfused CTALs sho wed that transepithelial Mg2+ and Ca2+ reabsorption were enhanced in CTALs from Mg2+-depleted, 8-week old animals, whereas transepithelial Mg2+ and Ca 2+ transport were not altered in 4-week-old mice. J(Na) and J(Cl) and the t ransepithelial potential (PDte) were not modified in CTALs from either anim al group. Our results suggest that a low-Mg2+ diet leads to urinary retenti on of Mg2+ and Ca2+ which is most likely due to increased Mg2+ and Ca2+ tra nsport in the CTAL. Furthermore, in response to dietary Mg2+ restriction, t he reabsorption of divalent cations in the CTAL of adult, but not of young, mice undergoes cellular adaptation.