title: Guanine nucleotides are potent secretagogues in permeabilized parathyroid cells.
abstract: We studied the effects of GTP and its' analogues on PTH release in permeabilized parathyroid cells to assess their role in mediating the unusual inverse relationship between Ca2+ and PTH release in intact parathyroid cells. Both 10-5 M GppNHp and GTP gamma S, nonhydrolysable analogues of GTP, produce up to an 8-fold enhancement of PTH release, which is dose-dependent. This effect is specific for GTP analogues as we could not mimic it with other nucleotides. 10(-3) M GDP beta S, a nonhydrolysable GDP analogue, completely abolishes GppNHp-stimulated hormone release, providing further support for mediation of this effect by a guanine-nucleotide regulatory protein. In GppNHp-stimulated cells, PTH release is maximal at free [Ca2+] less than 200 nM and progressively decreases as the free [Ca2+] increases from 300 nM to 100 microM. These results suggest the presence of a guanine-nucleotide binding protein in the parathyroid cell that may play an important role in the regulation of PTH secretion by Ca2+ and perhaps other secretagogues.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D002417:Cattle; D006150:Guanine Nucleotides / Q000494:pharmacology*; D066298:In Vitro Techniques; D009711:Nucleotides / Q000494:pharmacology; D010280:Parathyroid Glands / Q000187:drug effects* / Q000378:metabolism; D010281:Parathyroid Hormone / Q000378:metabolism*
chemical_list: D006150:Guanine Nucleotides; D009711:Nucleotides; D010281:Parathyroid Hormone; D002118:Calcium