Cardiac neuronal nitric oxide synthase isoform regulates myocardial contraction and calcium handling.
A neuronal isoform of nitric oxide synthase (nNOS) has recently been located to the cardiac sarcoplasmic reticulum (SR). Subcellular localization of a constitutive NOS in the proximity of an activating source of Ca2+ suggests that cardiac nNOS-derived NO may regulate contraction by exerting a highly specific and localized action on ion channels/transporters involved in Ca2+ cycling. To test this hypothesis, we have investigated myocardial Ca2+ handling and contractility in nNOS knockout mice (nNOS-/-) and in control mice (C) after acute nNOS inhibition with 100 micromol/L L-VNIO. nNOS gene disruption or L-VNIO increased basal contraction both in left ventricular (LV) myocytes (steady-state cell shortening 10.3+/-0.6% in nNOS-/- versus 8.1+/-0.5% in C; P<0.05) and in vivo (LV ejection fraction 53.5+/-2.7 in nNOS-/- versus 44.9+/-1.5% in C; P<0.05). nNOS disruption increased ICa density (in pA/pF, at 0 mV, -11.4+/-0.5 in nNOS-/- versus -9.1+/-0.5 in C; P<0.05) and prolonged the slow time constant of inactivation of ICa by 38% (P<0.05), leading to an increased Ca2+ influx and a greater SR load in nNOS-/- myocytes (in pC/pF, 0.78+/-0.04 in nNOS-/- versus 0.64+/-0.03 in C; P<0.05). Consistent with these data, [Ca2+]i transient (indo-1) peak amplitude was greater in nNOS-/- myocytes (410/495 ratio 0.34+/-0.01 in nNOS-/- versus 0.31+/-0.01 in C; P<0.05). These findings have uncovered a novel mechanism by which intracellular Ca2+ is regulated in LV myocytes and indicate that nNOS is an important determinant of basal contractility in the mammalian myocardium. The full text of this article is available at http://www.circresaha.org.
Sears
Claire E
CE
Department of Cardiovascular Medicine, Oxford University, John Radcliffe Hospital, Oxford, OX3 9DU, UK. claire.sears@cardiov.ox.ac.uk
Bryant
Simon M
SM
Ashley
Euan A
EA
Lygate
Craig A
CA
Rakovic
Stevan
S
Wallis
Helen L
HL
Neubauer
Stefan
S
Terrar
Derek A
DA
Casadei
B
B
D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D004553:Electric Conductivity; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology / Q000201:enzymology; D051379:Mice; D018345:Mice, Knockout; D009200:Myocardial Contraction; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology / Q000201:enzymology* / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D052248:Nitric Oxide Synthase Type I; D009952:Ornithine / Q000031:analogs & derivatives* / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D012519:Sarcoplasmic Reticulum / Q000737:chemistry / Q000201:enzymology; D016276:Ventricular Function
D015220:Calcium Channels; D004791:Enzyme Inhibitors; C111862:N(5)-(1-imino-3-butenyl)ornithine; D009952:Ornithine; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496321:Nos1 protein, mouse; D002118:Calcium