What contributes most significantly to the kidney's high energy expenditure?

It was discovered in an assessment of energy expenditure in chronic kidney disease patients that having a sedentary lifestyle is what contributes to high energy expenditure. Also, one of the procedures done on patients which is hemodialysis can also contribute to this.

It is the transportation of NaCl (Sodium Chloride)  in the high division of the ascending limb of the loop of Henle.

The Flat Ascending Limb of the Loop of Henle is penetrable to the chemical element NaCl (Sodium Chloride) which is not water. It causes tubular fluid throughout the descending limb in the body to the thick ascending limb of the body. It is impenetrable to water and urea without maybe perforable to Chlorine.

What are the choices?

Enzyme. anything that ends in "ase" is usually an enzyme.