title: Sympathetic control of heart rate in nNOS knockout mice.
abstract: Inhibition of neuronal nitric oxide synthase (nNOS) in cardiac postganglionic sympathetic neurons leads to enhanced cardiac sympathetic responsiveness in normal animals, as well as in animal models of cardiovascular diseases. We used isolated atria from mice with selective genetic disruption of nNOS (nNOS(-/-)) and their wild-type littermates (WT) to investigate whether sympathetic heart rate (HR) responses were dependent on nNOS. Immunohistochemistry was initially used to determine the presence of nNOS in sympathetic [tyrosine hydroxylase (TH) immunoreactive] nerve terminals in the mouse sinoatrial node (SAN). After this, the effects of postganglionic sympathetic nerve stimulation (1-10 Hz) and bath-applied norepinephrine (NE; 10(-8)-10(-4) mol/l) on HR were examined in atria from nNOS(-/-) and WT mice. In the SAN region of WT mice, TH and nNOS immunoreactivity was virtually never colocalized in nerve fibers. nNOS(-/-) atria showed significantly reduced HR responses to sympathetic nerve activation and NE (P < 0.05). Similarly, the positive chronotropic response to the adenylate cyclase activator forskolin (10(-7)-10(-5) mol/l) was attenuated in nNOS(-/-) atria (P < 0.05). Constitutive NOS inhibition with L-nitroarginine (0.1 mmol/l) did not affect the sympathetic HR responses in nNOS(-/-) and WT atria. The paucity of nNOS in the sympathetic innervation of the mouse SAN, in addition to the attenuated HR responses to neuronal and applied NE, indicates that presynaptic sympathetic neuronal NO does not modulate neuronal NE release and SAN pacemaking in this species. It appears that genetic deletion of nNOS results in the inhibition of adrenergic-adenylate cyclase signaling within SAN myocytes.
authors.affiliation: Department of Physiology, School of Biomedical Sciences, Monash University, 3800 Australia. Julia.Choate@med.monash.edu.au
authors.forename: J K
authors.initials: JK
authors.lastname: Choate
authors.forename: S M
authors.initials: SM
authors.lastname: Murphy
authors.forename: R
authors.initials: R
authors.lastname: Feldman
authors.forename: C R
authors.initials: CR
authors.lastname: Anderson
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002586:Cesium / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D020536:Enzyme Activators / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006325:Heart Atria / Q000294:innervation; D006339:Heart Rate / Q000187:drug effects; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009569:Nitric Oxide / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D019335:Nitroarginine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D012849:Sinoatrial Node / Q000187:drug effects / Q000294:innervation* / Q000378:metabolism; D017779:Sympathetic Fibers, Postganglionic / Q000187:drug effects / Q000201:enzymology*; D013566:Sympathomimetics / Q000494:pharmacology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
chemical_list: D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D013566:Sympathomimetics; D005576:Colforsin; D002586:Cesium; D019335:Nitroarginine; D009569:Nitric Oxide; D000242:Cyclic AMP; D052248:Nitric Oxide Synthase Type I; C496321:Nos1 protein, mouse; D014446:Tyrosine 3-Monooxygenase; D000262:Adenylyl Cyclases; D009638:Norepinephrine