AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 2 403-R413, Copyright © 1995 by American Physiological Society
Modulation of intrinsic cardiac neuronal activity by nitric oxide donors induces cardiodynamic changes
J. A. Armour, F. M. Smith, A. M. Losier, H. H. Ellenberger and D. A. Hopkins
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
Studies were performed to determine 1) whether a specific marker for nitric
oxide production is associated with canine intrinsic cardiac neurons, 2)
whether the transmembrane properties of these neurons can be altered by
nitric oxide donors, 3) whether in situ intrinsic cardiac neurons are
sensitive to nitric oxide donors, and 4) whether these neurons are involved
in cardiac regulation. Thirty to forty percent of canine intrinsic cardiac
neurons were labeled with a selective anatomic marker for nitric oxide
production. Nitric oxide donors modified the transmembrane properties of a
subpopulation of intrinsic cardiac neurons studied in vitro. The nitric
oxide donors nitroglycerine, sodium nitrite, and nitroprusside induced
concentration-dependent increases in neuronal activity frequently
associated with cardiac augmentation. Similar neuronal responses were
elicited by N-methyl-D-aspartate receptor activation as well as when the
precursor of nitric oxide, L-arginine, and the exogenous nitric oxide
donor, S-nitroso-N-acetylpenicillamine, were administered, indicating that
intrinsic cardiac neurons can be modulated by nitric oxide donors. Such
neurons apparently are tonically influenced by locally released nitric
oxide as local administration of the competitive inhibitor of nitric oxide
synthase, NG-nitro-L-arginine methyl ester, suppressed their spontaneous
activity. These data indicate that a significant population of nitric
oxide-sensitive neurons exists in the canine intrinsic cardiac nervous
system that are involved in cardiac regulation.
