title: Sustained signalling by PTH modulates IP3 accumulation and IP3 receptors through cyclic AMP junctions.
abstract: Parathyroid hormone (PTH) stimulates adenylyl cyclase through type 1 PTH receptors (PTH1R) and potentiates the Ca(2+) signals evoked by carbachol, which stimulates formation of inositol 1,4,5-trisphosphate (IP3). We confirmed that in HEK cells expressing PTH1R, acute stimulation with PTH(1-34) potentiated carbachol-evoked Ca(2+) release. This was mediated by locally delivered cyclic AMP (cAMP), but unaffected by inhibition of protein kinase A (PKA), exchange proteins activated by cAMP, cAMP phosphodiesterases (PDEs) or substantial inhibition of adenylyl cyclase. Sustained stimulation with PTH(1-34) causes internalization of PTH1R-adenylyl cyclase signalling complexes, but the consequences for delivery of cAMP to IP3R within cAMP signalling junctions are unknown. Here, we show that sustained stimulation with PTH(1-34) or with PTH analogues that do not evoke receptor internalization reduced the potentiated Ca(2+) signals and attenuated carbachol-evoked increases in cytosolic IP3. Similar results were obtained after sustained stimulation with NKH477 to directly activate adenylyl cyclase, or with the membrane-permeant analogue of cAMP, 8-Br-cAMP. These responses were independent of PKA and unaffected by substantial inhibition of adenylyl cyclase. During prolonged stimulation with PTH(1-34), hyperactive cAMP signalling junctions, within which cAMP is delivered directly and at saturating concentrations to its targets, mediate sensitization of IP3R and a more slowly developing inhibition of IP3 accumulation.
authors.affiliation: Department of Pharmacology, University of Cambridge, Cambridge, CB2 1PD, UK.
authors.forename: Abha
authors.initials: A
authors.lastname: Meena
authors.affiliation: Department of Pharmacology, University of Cambridge, Cambridge, CB2 1PD, UK.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Tovey
authors.affiliation: Department of Pharmacology, University of Cambridge, Cambridge, CB2 1PD, UK cwt1000@cam.ac.uk.
authors.forename: Colin W
authors.initials: CW
authors.lastname: Taylor
mesh_terms: D000262:Adenylyl Cyclases / Q000235:genetics* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002217:Carbachol / Q000008:administration & dosage; D005576:Colforsin / Q000008:administration & dosage; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000235:genetics* / Q000378:metabolism; D010281:Parathyroid Hormone / Q000008:administration & dosage / Q000378:metabolism; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000235:genetics* / Q000378:metabolism
chemical_list: D053496:Inositol 1,4,5-Trisphosphate Receptors; C473449:PTH1R protein, human; D010281:Parathyroid Hormone; D044168:Receptor, Parathyroid Hormone, Type 1; D005576:Colforsin; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D002118:Calcium
keywords: Ca2+ signalling; Cyclic AMP; Inositol trisphosphate receptor; Parathyroid hormone