title: Calcium inflow in cells transfected with cloned rat and porcine calcitonin receptors.
abstract: Ca2+ fluxes were examined in HEK 293 cells stably expressing the rat or porcine calcitonin receptors (CTRs). Calcitonin (CT) rapidly increased cytosolic Ca2+ ([Ca2+]i) concentrations in these cells in a manner which was sustained in the presence of extracellular Ca2+ ([Ca2+]e). In cells pretreated with CT, elevation of the [Ca2+]e concentration resulted in a further increase in [Ca2+]i which was concentration-dependent with respect to both the concentration of CT and the increment of [Ca2+]e. Untransfected cells, cells transfected with vector alone, and CTR-transfected cells not treated with CT, were unresponsive to [Ca2+]e. The microsomal Ca(2+)-ATPase inhibitor thapsigargin was able to mimic both the acute [Ca2+]i fluxes and responsiveness to [Ca2+]e mediated by CT in these cells. The CT-induced responsiveness to [Ca2+]e was neither mimicked by, nor affected by, activators of the cAMP or protein kinase C pathways. Treatment of cells with pertussis toxin influenced neither the primary Ca2+ fluxes in response to CT or thapsigargin nor the agonist-induced [Ca2+]e influx. Nifedipine failed to block responses to either CT or thapsigargin. These results lead to the important conclusion that the CTR participates in receptor-activated Ca2+ inflow, in which depletion of intracellular Ca2+ pools leads secondarily to influx of extracellular Ca2+.
authors.affiliation: St Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia.
authors.forename: D M
authors.initials: DM
authors.lastname: Findlay
authors.forename: S
authors.initials: S
authors.lastname: Houssami
authors.forename: P M
authors.initials: PM
authors.lastname: Sexton
authors.forename: C L
authors.initials: CL
authors.lastname: Brady
authors.forename: T J
authors.initials: TJ
authors.lastname: Martin
authors.forename: D E
authors.initials: DE
authors.lastname: Myers
mesh_terms: D000818:Animals; D002116:Calcitonin / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D018014:Gene Transfer Techniques; D006801:Humans; D017136:Ion Transport; D051381:Rats; D018003:Receptors, Calcitonin / Q000235:genetics / Q000378:metabolism*; D013552:Swine; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
chemical_list: D018003:Receptors, Calcitonin; D013729:Terpenes; D019284:Thapsigargin; D002116:Calcitonin; D002118:Calcium