title: Inhibition of the calcium pump by human parathyroid hormone-(1-34) and human calcitonin in liver plasma membranes.
abstract: The effect of human parathyroid hormone-(1-34) (hPTH) and human calcitonin (hCT) on the activity of the Ca2(+)-extrusion pump in liver plasma membranes was studied. Both hormones were found to be potent inhibitors of Ca2+ transport and the related high-affinity (Ca2(+)-Mg2+)-ATPase activity, causing maximal inhibition of 25-30% at concentrations of 100 nM. Half-maximal inhibition was observed with 20 nM-hPTH and with 0.5 nM-hCT. By comparison, salmon calcitonin and intact bovine parathyroid hormone-(1-84) were inhibitory only at 10 microM. The effects of hCT and hPTH on the Ca2+ pump activity were not mimicked by cyclic AMP. Also, 10 microM of either hPTH-(1-34) or hCT did not alter the 45Ca2+ influx rate into isolated hepatocytes. We conclude that inhibition of Ca2+ efflux, rather than the stimulation of Ca2+ influx, may play a functional role in the control of hepatic calcium homeostasis by hPTH-(1-34) and hCT.
authors.affiliation: Department of Biochemistry, McMaster University, Health Sciences Centre, Hamilton, Ontario, Canada.
authors.forename: R C
authors.initials: RC
authors.lastname: McKenzie
authors.forename: S
authors.initials: S
authors.lastname: Lotersztajn
authors.forename: C
authors.initials: C
authors.lastname: Pavoine
authors.forename: F
authors.initials: F
authors.lastname: Pecker
authors.forename: R M
authors.initials: RM
authors.lastname: Epand
authors.forename: R C
authors.initials: RC
authors.lastname: Orlowski
mesh_terms: D001693:Biological Transport, Active; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002116:Calcitonin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology; D006801:Humans; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D019379:Teriparatide
chemical_list: D015220:Calcium Channels; D010281:Parathyroid Hormone; D010446:Peptide Fragments; D019379:Teriparatide; D002116:Calcitonin; D000242:Cyclic AMP; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium