Parathyroid-specific interaction of the calcium-sensing receptor and G alpha q.

The calcium-sensing receptor regulates various parathyroid gland functions, including hormone secretion, gene transcription, and chief cell hyperplasia through G alpha q- and G alpha i-dependent signaling pathways. To determine the specific function of G alpha q in these processes, we generated transgenic mice using the human parathyroid hormone promoter to drive overexpression of a dominant negative G alpha q loop minigene to selectively disrupt G alpha q function in the parathyroid gland. The G alpha q loop mRNA was highly expressed in the parathyroid gland but not in other tissues of these transgenic mice. Gross appearance, body weight, bone mineral density, and survival of the transgenic mice were indistinguishable from those of their wild-type littermates. Adult transgenic mice, however, exhibited an increase in parathyroid hormone mRNA and in its basal serum level as well as in gland size. The response of the parathyroid gland to hypocalcemia was found to be reduced in sensitivity in the transgenic mice when compared to their wild-type controls. Abnormalities of the parathyroid gland function in these transgenic mice were similar to those of heterozygous G alpha q(+/-) and calcium sensing receptor(+/-) mice. These studies demonstrate the feasibility of selectively targeting the parathyroid gland to investigate signaling mechanisms downstream of the calcium receptor.