CASR and Hypocalcemia: By sensing even minute changes in the Cao2+ from its normal level, CaSR modulates the functions of key tissues, especially the parathyroid glands and the kidneys.5 In the parathyroid glands, CaSR senses perturbations in the Cao2+ level of only a few percent and then responds to the hypocalcemia by increasing PTH secretion, stabilizing mRNA and inducing the proliferation of parathyroid cells.