AJP - Heart and Circulatory Physiology, Vol 253, Issue 6 1618-H1622, Copyright © 1987 by American Physiological Society
Angiotensin II binding sites in the conduction system of rat hearts
K. Saito, J. S. Gutkind and J. M. Saavedra
Section on Clinical Pharmacology, National Institute of Mental Health, Bethesda, Maryland 20892.
Angiotensin II binding sites were localized and quantified in the
conduction system of the rat heart by autoradiography in combination with
computerized microdensitometry. Tissue sections (16-microns thick),
containing cardiac vagus ganglia, sinus node, and atrioventricular node,
were incubated with 125I-Sar1-angiotensin II to generate autoradiograms
that were compared with other autoradiograms from 125I-labeled standards.
Angiotensin II binding sites were highly localized in both the sinoatrial
and atrioventricular nodes and in the cardiac vagus ganglia. In contrast,
binding to the angiotensin converting enzyme, determined by incubation of
adjacent tissue sections with the specific enzyme inhibitor 125I-351A, was
very low in these areas but high in the cardiac endothelium. Our results
suggest that angiotensin II may have direct chronotropic effects through
stimulation of specific receptors in the conduction system of the heart and
in intrinsic parasympathetic ganglia.
