Calcium is one of the key elements required for maintenance and survival of life in animals with both endo- and exoskeletons. Because there is a wide variation in dietary calcium (dependent upon the local habitat) and dietary practices, and because there is a changing physiological need throughout life (e.g., for mammals, during growth, puberty, pregnancy, lactation, and menopause), it is
... [Show full abstract] essential that the process of intestinal calcium absorption be adaptable and responsive to both the dietary and physiological circumstances. This article reviews the evidence that transcaltachia, or the rapid stimulation of intestinal Ca2+ transport by the steroid hormone, lα, 25(OH)2-vitamin D3, as studied in the chicken, meets many of the objectives of an adaptive intestinal calcium transport process. Transcaltachia is studied in a perfused chick duodenum, where 45Ca2+ is placed in the lumen and potential agonists are perfused into the celiac artery; the transcaltachic reponse represents the stimulation within 4–8 min of the transfer of 45Ca2+ from the lumen to the vascular perfusate. lα,25(OH)2-vitamin D3 stimulation of transcaltachia occurs via nongenomic mechanisms which involve a plasma membrane receptor for the secosteroid and the coupled opening of voltage-gated Ca2+ channels on the basal lateral membrane of the intestinal epithelial cell and the activation of the second messengers, protein kinase C and cAMP.
