Calcium and magnesium transport in the cortical thick ascending limb of Henle’s loop: influence of age and gender

Abstract

 Previous studies from our laboratory have shown that Ca²⁺ and Mg²⁺ absorption in the mouse cortical thick ascending limb of Henle’s loop (cTAL) is a passive, paracellular process driven by the transepithelial voltage. The passive permeability of the epithelium is enhanced by peptide hormones. The present study investigated whether divalent cation absorption 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 tubules were perfused in vitro at a luminal flow rate of 1.5 to 2.5 nl/min. 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 (PD_te) was measured continuously. No differences were found in the PD_te, J _Na and J _Cl of the various animal groups but the transepithelial Ca²⁺ and Mg²⁺ transport capacity of the cTAL was higher in adults (8 weeks) than in young animals (4 weeks). Furthermore, irrespective of age, transepithelial Ca²⁺ net absorption was greater in male than in female animals. In contrast, the NaCl transport was maximal at 4 weeks in both genders. We conclude therefore that transepithelial divalent cation absorption in the mouse cTAL is an inductive process influenced by cell maturation and gender. The molecular basis of these inductions remains to be elucidated.