title: Parathyroid hormone increases sodium/calcium exchange activity in renal cells and the blunting of the response in aging.
abstract: Na+-dependent Ca2+ efflux was demonstrated in cells isolated from the rat renal cortex, suggestive of the presence of a Na+/Ca2+ exchange carrier in the cells. Parathyroid hormone, when incubated with the cells in vitro, increased Na+-dependent Ca2+ efflux about 60%. The effect of the hormone was specific for biologically active parathyroid hormone analogs and could be mimicked by cyclic nucleotides and forskolin. The effects of parathyroid hormone concentration on Ca2+ efflux and cyclic AMP formation were similar. These findings would be consistent with the view that the cyclic nucleotide might act as the intracellular messenger to increase Na+/Ca2+ exchange activity. Cells isolated from parathyroidectomized rats had decreased Na+-dependent Ca2+ efflux. When these cells were treated in vitro with parathyroid hormone, Na+-dependent Ca2+ efflux was enhanced to the same rate as found with cells from sham-operated animals. Parathyroid hormone-sensitive Na+/Ca2+ exchange activity was markedly blunted in cells from senescent (24 months) rats. Basal Na+-dependent Ca2+ efflux and Na+-independent Ca2+ efflux were not altered in the aged animal. Parathyroid-stimulated adenylate cyclase was also decreased in aging. In contrast, forskolin-stimulated Na+-dependent Ca2+ efflux and adenylate cyclase did not change with senescence. These findings would be compatible with a mechanism of desensitization that occurred at the level of the receptor or hormone-receptor coupling to adenylate cyclase. These results may be of physiological significance in understanding calcium homeostasis and the imbalances in mineral metabolism associated with old age.
mesh_terms: D000375:Aging; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002794:Choline / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010280:Parathyroid Glands / Q000502:physiology; D010281:Parathyroid Hormone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D010281:Parathyroid Hormone; D005576:Colforsin; D012965:Sodium Chloride; D012964:Sodium; D000242:Cyclic AMP; D002794:Choline; D002118:Calcium