title: Trifluoperazine: a rynodine receptor agonist.
abstract: Trifluoperazine (TFP), a phenothiazine, is a commonly used antipsychotic drug whose therapeutic effects are attributed to its central anti-adrenergic and anti-dopaminergic actions. However, TFP is also a calmodulin (CaM) antagonist and alters the Ca(2+) binding properties of calsequestrin (CSQ). The CaM and CSQ proteins are known modulators of sarcoplasmic reticulum (SR) Ca(2+) release in ventricular myocytes. We explored TFP actions on cardiac SR Ca(2+) release in cells and single type-2 ryanodine receptor (RyR2) channel activity in bilayers. In intact and permeabilized ventricular myocytes, TFP produced an initial activation of RyR2-mediated SR Ca(2+) release and over time depleted SR Ca(2+) content. At the single channel level, TFP or nortryptiline (NRT; a tricyclic antidepressant also known to modify CSQ Ca(2+) binding) increased the open probability (Po) of CSQ-free channels with an EC(50) of 5.2 microM or 8.9 microM (respectively). This Po increase was due to elevated open event frequency at low drug concentrations while longer mean open events sustained Po at higher drug concentrations. Activation of RyR2 by TFP occurred in the presence or absence of CaM. TFP may also inhibit SR Ca uptake as well as increase RyR2 opening. Our results suggest TFP and NRT can alter RyR2 function by interacting with the channel protein directly, independent of its actions on CSQ or CaM. This direct action may contribute to the clinical adverse cardiac side effects associated with these drugs.
authors.affiliation: Department of Molecular Biophysics and Physiology, Rush University Medical Center, 1750 W. Harrison Ave, Chicago, IL, 60612, USA.
authors.forename: Jia
authors.initials: J
authors.lastname: Qin
authors.forename: Aleksey V
authors.initials: AV
authors.lastname: Zima
authors.forename: Maura
authors.initials: M
authors.lastname: Porta
authors.forename: Lothar A
authors.initials: LA
authors.lastname: Blatter
authors.forename: Michael
authors.initials: M
authors.lastname: Fill
mesh_terms: D000818:Animals; D002120:Calcium Channel Agonists / Q000008:administration & dosage*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002415:Cats; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000502:physiology*; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D014268:Trifluoperazine / Q000008:administration & dosage*; D016277:Ventricular Function, Left / Q000187:drug effects*
chemical_list: D002120:Calcium Channel Agonists; D019837:Ryanodine Receptor Calcium Release Channel; D014268:Trifluoperazine