Calcium transport in renal epithelial cells.

Extracellular calcium homeostasis involves coordinated calcium absorption by the intestine, calcium resorption from bone, and calcium reabsorption by the kidney. This review addresses the mechanism and regulation of renal calcium transport. Calcium reabsorption occurs throughout the nephron. However, distal tubules are the nephron site at which calcium reabsorption is regulated by parathyroid hormone, calcitonin, and 1 alpha,25-dihydroxyvitamin D3 and where the magnitude of net reabsorption is largely determined. These and related observations underscore the view that distal tubules are highly specialized to permit fine regulation of calcium excretion in response to alterations in extracellular calcium levels. Progress in understanding the mechanism and regulation of calcium transport has emerged from application of single cell fluorescence, patch clamp, and molecular biological approaches. These techniques permit the examination of ion transport at the cellular level and its regulation at subcellular and molecular levels. This editorial review focuses on recent and emerging observations and attempts to integrate them into models of cellular calcium transport.