 Since Na⁺ ion concentration is a major determinant of extracellular fluid osmolarity, changes in Na⁺ concentration affect the movement of fluids and consequently fluid volume and blood pressure.The activity of ENaC in the colon and kidney is modulated by the mineralcorticoid aldosterone.It can be blocked by either triamterene or amiloride, which are used medically to serve as diuretics.