Nitric oxide regulation of myocardial contractility and calcium cycling: independent impact of neuronal and endothelial nitric oxide synthases.
The mechanisms by which nitric oxide (NO) influences myocardial Ca2+ cycling remain controversial. Because NO synthases (NOS) have specific spatial localization in cardiac myocytes, we hypothesized that neuronal NOS (NOS1) found in cardiac sarcoplasmic reticulum (SR) preferentially regulates SR Ca2+ release and reuptake resulting in potentiation of the cardiac force-frequency response (FFR). Transesophageal pacing (660 to 840 bpm) in intact C57Bl/6 mice (WT) stimulated both contractility (dP/dtmax normalized to end-diastolic volume; dP/dt-EDV) by 51+/-5% (P<0.001) and lusitropy (tau; tau) by 20.3+/-2.0% (P<0.05). These responses were markedly attenuated in mice lacking NOS1 (NOS1-/-) (15+/-2% increase in dP/dt-EDV; P<0.001 versus WT; and no change in tau; P<0.01 versus WT). Isolated myocytes from NOS1-/- (approximately 2 months of age) also exhibited suppressed frequency-dependent sarcomere shortening and Ca2+ transients ([Ca2+]i) compared with WT. SR Ca2+ stores, a primary determinant of the FFR, increased at higher frequencies in WT (caffeine-induced [Ca2+]i at 4 Hz increased 107+/-23% above 1 Hz response) but not in NOS1-/- (13+/-26%; P<0.01 versus WT). In contrast, mice lacking NOS3 (NOS3-/-) had preserved FFR in vivo, as well as in isolated myocytes with parallel increases in sarcomere shortening, [Ca2+]i, and SR Ca2+ stores. NOS1-/- had increased SR Ca2+ ATPase and decreased phospholamban protein abundance, suggesting compensatory increases in SR reuptake mechanisms. Together these data demonstrate that NOS1 selectively regulates the cardiac FFR via influences over SR Ca2+ cycling. Thus, there is NOS isoform-specific regulation of different facets of rate-dependent excitation-contraction coupling; inactivation of NOS1 has the potential to contribute to the pathophysiology of states characterized by diminished frequency-dependent inotropic responses.
Khan
Shakil A
SA
Department of Medicine, The Johns Hopkins Medical Institution, Baltimore, Md, USA.
Skaf
Michel W
MW
Harrison
Robert W
RW
Lee
Kwangho
K
Minhas
Khalid M
KM
Kumar
Anil
A
Fradley
Mike
M
Shoukas
Artin A
AA
Berkowitz
Dan E
DE
Hare
Joshua M
JM
D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D048429:Cell Size / Q000502:physiology; D004558:Electric Stimulation; D005260:Female; D005838:Genotype; D006439:Hemodynamics / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D009124:Muscle Proteins / Q000378:metabolism; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D012518:Sarcomeres / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D016277:Ventricular Function, Left / Q000502:physiology
D009124:Muscle Proteins; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496321:Nos1 protein, mouse; C496315:Nos3 protein, mouse; D002118:Calcium