title: Phospholemman modulates Na+/Ca2+ exchange in adult rat cardiac myocytes.
abstract: Previous studies have shown that overexpression of phospholemman (PLM) affected contractile function and Ca(2+) homeostasis in adult rat myocytes. We tested the hypothesis that PLM modulated Na(+)/Ca(2+) exchanger (NCX1) activity. PLM was overexpressed in adult rat myocytes by adenovirus-mediated gene transfer. After 72 h, the half-time of relaxation from caffeine-induced contracture, an estimate of forward NCX1 activity, was prolonged 1.8-fold (P < 0.003) in myocytes overexpressing PLM compared with control myocytes overexpressing green fluorescent protein alone. Reverse NCX1 current (3 Na(+) out:1 Ca(2+) in) was significantly (P < 0.0001) lower in PLM myocytes, especially at more positive voltages. Immunofluorescence demonstrated colocalization of PLM and NCX1 to the plasma membrane and t-tubules. Resting membrane potential, action potential amplitude and duration, myocyte size, and NCX1 and calsequestrin protein levels were not affected by PLM overexpression. At 5 mM extracellular [Ca(2+)] ([Ca(2+)](o)), the depressed contraction amplitudes in PLM myocytes were increased towards normal by cooverexpression with NCX1. At 0.6 mM [Ca(2+)](o), the supranormal contraction amplitudes in PLM myocytes were reduced by cooverexpression with NCX1. We conclude that PLM modulated myocyte contractility partly by inhibiting Na(+)/Ca(2+) exchange.
authors.affiliation: Weis Center for Research and Department of Medicine, Geisinger Medical Center, Danville, Pennsylvania 17822, USA.
authors.forename: Xue-Qian
authors.initials: XQ
authors.lastname: Zhang
authors.forename: Anwer
authors.initials: A
authors.lastname: Qureshi
authors.forename: Jianliang
authors.initials: J
authors.lastname: Song
authors.forename: Lois L
authors.initials: LL
authors.lastname: Carl
authors.forename: Qiang
authors.initials: Q
authors.lastname: Tian
authors.forename: Richard C
authors.initials: RC
authors.lastname: Stahl
authors.forename: David J
authors.initials: DJ
authors.lastname: Carey
authors.forename: Lawrence I
authors.initials: LI
authors.lastname: Rothblum
authors.forename: Joseph Y
authors.initials: JY
authors.lastname: Cheung
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D008297:Male; D008565:Membrane Proteins / Q000493:pharmacokinetics / Q000494:pharmacology*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D010750:Phosphoproteins / Q000493:pharmacokinetics / Q000494:pharmacology*; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000378:metabolism* / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects
chemical_list: D008565:Membrane Proteins; D010750:Phosphoproteins; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; C069141:phospholemman; D002110:Caffeine