title: Cyclosporin A inhibits inositol 1,4,5-trisphosphate-dependent Ca2+ signals by enhancing Ca2+ uptake into the endoplasmic reticulum and mitochondria.
abstract: Cytosolic Ca(2+) ([Ca(2+)](i)) oscillations may be generated by the inositol 1,4,5-trisphosphate receptor (IP(3)R) driven through cycles of activation/inactivation by local Ca(2+) feedback. Consequently, modulation of the local Ca(2+) gradients influences IP(3)R excitability as well as the duration and amplitude of the [Ca(2+)](i) oscillations. In the present work, we demonstrate that the immunosuppressant cyclosporin A (CSA) reduces the frequency of IP(3)-dependent [Ca(2+)](i) oscillations in intact hepatocytes, apparently by altering the local Ca(2+) gradients. Permeabilized cell experiments demonstrated that CSA lowers the apparent IP(3) sensitivity for Ca(2+) release from intracellular stores. These effects on IP(3)-dependent [Ca(2+)](i) signals could not be attributed to changes in calcineurin activity, altered ryanodine receptor function, or impaired Ca(2+) fluxes across the plasma membrane. However, CSA enhanced the removal of cytosolic Ca(2+) by sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA), lowering basal and inter-spike [Ca(2+)](i). In addition, CSA stimulated a stable rise in the mitochondrial membrane potential (DeltaPsi(m)), presumably by inhibiting the mitochondrial permeability transition pore, and this was associated with increased Ca(2+) uptake and retention by the mitochondria during a rise in [Ca(2+)](i). We suggest that CSA suppresses local Ca(2+) feedback by enhancing mitochondrial and endoplasmic reticulum Ca(2+) uptake, these actions of CSA underlie the lower IP(3) sensitivity found in permeabilized cells and the impaired IP(3)-dependent [Ca(2+)](i) signals in intact cells. Thus, CSA binding proteins (cyclophilins) appear to fine tune agonist-induced [Ca(2+)](i) signals, which, in turn, may adjust the output of downstream Ca(2+)-sensitive pathways.
authors.affiliation: Departamento de Farmacologia, Universidade Federal de São Paulo 04044, UNIFESP-EPM, São Paulo 04044, Brazil.
authors.forename: S S
authors.initials: SS
authors.lastname: Smaili
authors.forename: K A
authors.initials: KA
authors.lastname: Stellato
authors.forename: P
authors.initials: P
authors.lastname: Burnett
authors.forename: A P
authors.initials: AP
authors.lastname: Thomas
authors.forename: L D
authors.initials: LD
authors.lastname: Gaspers
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000037:antagonists & inhibitors*; D007425:Intracellular Membranes / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D007166:Immunosuppressive Agents; D016572:Cyclosporine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium