One Small Region of a Human Kidney Tubule Known as the Thick

Multiple Choice

One small region of a human kidney tubule known as the thick ascending limb (or TAL) has tight junctions that are permeable to magnesium (Mg²⁺) ions. What is thought to account for the permeability of this tight junction to magnesium ions?

A) The membrane in this region is leaky because of special phospholipids.
B) Loops of claudin molecules that extend into the extracellular space form pores in the TAL.
C) Loops of claudin molecules that extend into the cytoplasm form pores in the TAL.
D) Loops of claudin molecules fully embedded in the TAL membrane form pores in the TAL.
E) Claudin molecules form gap junctions that allow the passage of magnesium ions.