An investigator perfuses isolated thick ascending limb segments with a solution containing a selective inhibitor of the apical Na⁺/K⁺/2Cl⁻ cotransporter. After 30 minutes, tubular fluid collected directly from the perfused segments is analyzed. Compared to control segments, the experimental segments show markedly increased calcium and magnesium concentrations in the collected tubular fluid. Sodium and chloride concentrations are also elevated, and the epithelium remains impermeable to water throughout the experiment.
Which of the following best explains the increased calcium and magnesium in tubular fluid?