Calcium-ion–sensing cell-surface receptors

Calcium ions are essential for a wide variety of biologic functions, including vital extracellular processes, such as blood clotting, intercellular adhesion, and skeletal integrity, as well as intracellular processes, such as the regulation of hormonal secretion, cell division, and cell motility.¹–⁴ Complex, free-living terrestrial organisms must maintain a near-constant concentration of extracellular calcium. How the body maintains and regulates extracellular calcium levels is a complex puzzle that has intrigued researchers for decades.³–⁵ One large piece of this puzzle that is falling into place concerns a cell-surface receptor that responds to, or “senses,” extracellular calcium-ion concentrations in parathyroid, kidney,.