Fig. 2.

Mg²⁺ handling in the thick ascending limb of Henle (TAL). The tight junction proteins claudin-16 and -19 form the Ca²⁺- and Mg²⁺-permeable channel. Mg²⁺ or Ca²⁺ in the circulation could activate the basolateral calcium-sensing receptor (CaSR), which exerts inhibitory effects on the tight junction claudin complex. Basolateral Na-K-ATPase provides the driving force for the apical Na-K-2Cl cotransporter (NKCC2) and parallel K⁺ excretion via ROMK, generating a favorable positive luminal voltage to facilitate paracellular Mg²⁺ and Ca²⁺ absorption.