CALCIUM AND MAGNESIUM TRANSPORT IN THE CORTICAL THICK ASCENDING LIMB OF HENLES LOOP - INFLUENCE OF AGE AND GENDER

Previous studies from our laboratory have shown that Ca2+ and Mg2+ abs orption in the mouse cortical thick ascending limb of Henle's loop (cT AL) is a passive, paracellular process driven by the transepithelial v oltage. The passive permeability of the epithelium is enhanced by pept ide hormones. The present study investigated whether divalent cation a bsorption in the cTAL is influenced by cell maturation and/or gender. For this purpose, mouse cTAL segments were microdissected from kidneys of female and male animals aged 4 and 8 weeks. The microdissected tub ules were perfused in vitro at a luminal flow rate of 1.5 to 2.5 nl/mi n. Transepithelial Na+, Cl-, Ca2+ and Mg2+ net fluxes (J(x), pmol.min( -1).mm(-1)) were measured using electron microprobe analysis, and the transepithelial potential difference (PDte) was measured continuously. No differences were found in the PDte, J(Na) and J(Cl) of the various animal groups but the transepithelial Ca2+ and Mg2+ transport capacit y of the cTAL was higher in adults (8 weeks) than in young animals (4 weeks). Furthermore, irrespective of age, transepithelial Ca2+ net abs orption was greater in male than in female animals. In contrast, the N aCl transport was maximal at 4 weeks in both genders. We conclude ther efore that transepithelial divalent cation absorption in the mouse cTA L is an inductive process influenced by cell maturation and gender. Th e molecular basis of these inductions remains to be elucidated.