Conditional neuronal nitric oxide synthase overexpression impairs myocardial contractility.
The role of the neuronal NO synthase (nNOS or NOS1) enzyme in the control of cardiac function still remains unclear. Results from nNOS(-/-) mice or from pharmacological inhibition of nNOS are contradictory and do not pay tribute to the fact that probably spatial confinement of the nNOS enzyme is of major importance. We hypothesize that the close proximity of nNOS and certain effector molecules like L-type Ca(2+)-channels has an impact on myocardial contractility. To test this, we generated a new transgenic mouse model allowing conditional, myocardial specific nNOS overexpression. Western blot analysis of transgenic nNOS overexpression showed a 6-fold increase in nNOS protein expression compared with noninduced littermates (n=12; P<0.01). Measuring of total NOS activity by conversion of [(3)H]-l-arginine to [(3)H]-l-citrulline showed a 30% increase in nNOS overexpressing mice (n=18; P<0.05). After a 2 week induction, nNOS overexpression mice showed reduced myocardial contractility. In vivo examinations of the nNOS overexpressing mice revealed a 17+/-3% decrease of +dp/dt(max) compared with noninduced mice (P<0.05). Likewise, ejection fraction was reduced significantly (42% versus 65%; n=15; P<0.05). Interestingly, coimmunoprecipitation experiments indicated interaction of nNOS with SR Ca(2+)ATPase and additionally with L-type Ca(2+)- channels in nNOS overexpressing animals. Accordingly, in adult isolated cardiac myocytes, I(Ca,L) density was significantly decreased in the nNOS overexpressing cells. Intracellular Ca(2+)-transients and fractional shortening in cardiomyocytes were also clearly impaired in nNOS overexpressing mice versus noninduced littermates. In conclusion, conditional myocardial specific overexpression of nNOS in a transgenic animal model reduced myocardial contractility. We suggest that nNOS might suppress the function of L-type Ca(2+)-channels and in turn reduces Ca(2+)-transients which accounts for the negative inotropic effect.
Burkard
Natalie
N
Department of Internal Medicine I, University of Wuerzburg, Wuerzburg, Germany.
Rokita
Adam G
AG
Kaufmann
Susann G
SG
Hallhuber
Matthias
M
Wu
Rongxue
R
Hu
Kai
K
Hofmann
Ulrich
U
Bonz
Andreas
A
Frantz
Stefan
S
Cartwright
Elizabeth J
EJ
Neyses
Ludwig
L
Maier
Lars S
LS
Maier
Sebastian K G
SK
Renné
Thomas
T
Schuh
Kai
K
Ritter
Oliver
O
D000818:Animals; D001120:Arginine / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000502:physiology; D020013:Calcium Signaling / Q000235:genetics / Q000502:physiology*; D048429:Cell Size; D002478:Cells, Cultured / Q000502:physiology; D002956:Citrulline / Q000096:biosynthesis; D006152:Cyclic GMP / Q000378:metabolism; D004318:Doxycycline / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D015640:Ion Channel Gating / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000201:enzymology / Q000502:physiology; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009952:Ornithine / Q000031:analogs & derivatives / Q000494:pharmacology; D025941:Protein Interaction Mapping; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000502:physiology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000502:physiology; D013318:Stroke Volume; D014463:Ultrasonography; D018487:Ventricular Dysfunction, Left / Q000000981:diagnostic imaging / Q000201:enzymology* / Q000503:physiopathology
D020746:Calcium Channels, L-Type; C111862:N(5)-(1-imino-3-butenyl)ornithine; D011993:Recombinant Fusion Proteins; D002956:Citrulline; D002110:Caffeine; D001120:Arginine; D009952:Ornithine; D052248:Nitric Oxide Synthase Type I; C496321:Nos1 protein, mouse; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D006152:Cyclic GMP; D004318:Doxycycline; D002118:Calcium