title: Na+/Ca2+ exchanger overexpression impairs frequency- and ouabain-dependent cell shortening in adult rat cardiomyocytes.
abstract: The Na(+)/Ca(2+) exchanger (NCX) may influence cardiac function depending on its predominant mode of action, forward mode or reverse mode, during the contraction-relaxation cycle. The intracellular Na(+) concentration ([Na(+)](i)) and the duration of the action potential as well as the level of NCX protein expression regulate the mode of action of NCX. [Na(+)](i) and NCX expression have been reported to be increased in human heart failure. Nevertheless, the consequences of altered NCX expression in heart failure are still a matter of discussion. We aimed to characterize the influence of NCX expression on intracellular Ca(2+) transport in rat cardiomyocytes by adenoviral-mediated gene transfer. A five- to ninefold (dose dependent) overexpression of NCX protein was achieved after 48 h by somatic gene transfer (Ad.NCX.GFP) versus control (Ad.GFP). NCX activity, determined by Na(+) gradient-dependent (45)Ca(2+)-uptake, was significantly increased. The protein expressions of sarco(endo)plasmic reticulum Ca(2+)-ATPase, phospholamban, and calsequestrin were unaffected by NCX overexpression. Fractional shortening (FS) of isolated cardiomyocytes was significantly increased at low stimulation rates in Ad.NCX.GFP. After a step-wise enhancing frequency of stimulation to 3.0 Hz, FS remained unaffected in Ad.GFP cells but declined in Ad.NCX.GFP cells. The positive inotropic effect of the cardiac glycoside ouabain was less effective in Ad.NCX.GFP cells, whereas the positive inotropic effect of beta-adrenergic stimulation remained unchanged. In conclusion, NCX overexpression results in a reduced cell shortening at higher stimulation frequencies as well as after inhibition of sarcolemmal Na(+)-K(+)-ATPase, i.e., in conditions with enhanced [Na(+)](i). At low stimulation rates, increased NCX expression enhances both intracellular systolic Ca(2+) and contraction amplitude.
authors.affiliation: Laboratory of Muscle Research and Molecular Cardiology, Dept. of Internal Medicine III, Univ. of Cologne, Joseph-Stelzmann Strasse 9, 50924 Cologne, Germany.
authors.forename: Birgit
authors.initials: B
authors.lastname: Bölck
authors.forename: Götz
authors.initials: G
authors.lastname: Münch
authors.forename: Peter
authors.initials: P
authors.lastname: Mackenstein
authors.forename: Martin
authors.initials: M
authors.lastname: Hellmich
authors.forename: Ingo
authors.initials: I
authors.lastname: Hirsch
authors.forename: Hannes
authors.initials: H
authors.lastname: Reuter
authors.forename: Nadja
authors.initials: N
authors.lastname: Hattebuhr
authors.forename: Hans-Jörg
authors.initials: HJ
authors.lastname: Weig
authors.forename: Martin
authors.initials: M
authors.lastname: Ungerer
authors.forename: Klara
authors.initials: K
authors.lastname: Brixius
authors.forename: Robert H G
authors.initials: RH
authors.lastname: Schwinger
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002316:Cardiotonic Agents / Q000494:pharmacology; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004285:Dogs; D015870:Gene Expression; D018014:Gene Transfer Techniques; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D007668:Kidney / Q000166:cytology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000235:genetics* / Q000378:metabolism*
chemical_list: D000318:Adrenergic beta-Agonists; D002316:Cardiotonic Agents; D019831:Sodium-Calcium Exchanger; D010042:Ouabain; D012964:Sodium; D017868:Cyclic AMP-Dependent Protein Kinases; D007545:Isoproterenol; D002118:Calcium