Autonomic regulation of pacemaker activity: role of heart nitric oxide synthases.
In autonomic-blocked rats treated with NG-nitro-L-arginine methyl ester (L-NAME, 7.5 mg/kg), heart rate increased 18% and mean arterial pressure increased 48%. Thyroidectomy, along with autonomic blockade, hampered the chronotropic response but did not modify the effect on blood pressure. After 150 min of autonomic blockade, the experimental end point, total nitric oxide (NO) production by heart NO synthases (NOS) decreased 61%: from 54 to 21 nmol NO.min-1.g heart-1. Mitochondrial NOS (mtNOS) and sarcoplasmic reticulum endothelial NOS activities decreased 74% and 52%, respectively. Mitochondria isolated from whole heart showed a well-coupled oxidative phosphorylation with high respiratory control and ADP-to-O ratios, decreased mtNOS activity (55-60%), and decreased mtNOS protein expression (70%). Immunohistochemistry with anti-inducible NOS antibody linked to gold particles localized mtNOS at the inner mitochondrial membranes. Histochemical right atrial NOS (NADPH-diaphorase) decreased 55% after heart denervation. The effects of autonomic denervation on the NO system were partially prevented by thyroidectomy performed simultaneously with autonomic blockade. Western blot analysis indicated a very rapid mtNOS protein turnover (half time=120 min) with a process of protein expression that was upregulated by thyroidectomy and a degradation process that was downregulated by the autonomic nervous system. The observations suggest that NO-mediated pathways contribute to pacemaker heart activity, likely through the NO steady-state levels in the right atrium and the whole heart.
Fellet
Andrea L
AL
Department of Physiology, Laboratory of Free Radical Biology, School of Pharmacy and Biochemistry, University of Buenos Aires, Argentina. afellet@ffyb.uba.ar
Balaszczuk
Ana M
AM
Arranz
Cristina
C
López-Costa
Juan José
JJ
Boveris
Alberto
A
Bustamante
Juanita
J
D000818:Animals; D016275:Atrial Function; D001341:Autonomic Nervous System / Q000502:physiology*; D001683:Biological Clocks / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D008297:Male; D008929:Mitochondria, Heart / Q000378:metabolism / Q000648:ultrastructure; D009206:Myocardium / Q000201:enzymology* / Q000648:ultrastructure; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013965:Thyroidectomy
D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D019331:NG-Nitroarginine Methyl Ester