Measurement of an organism's, organ's, tissue's or cell's capacity to respond, such as by a change in activity, state or condition, to potassium chloride, the salt of the potassium cation (K+) and the chlorine/chloride anion (Cl-). Potassium chloride is used as an eletroylyte replenisher and has mild vasoconstrictive properties when applied directly to blood vessels.