AJP - Heart and Circulatory Physiology, Vol 250, Issue 3 490-H497, Copyright © 1986 by American Physiological Society
Differences in affinity of cardiac beta-adrenergic receptors for [3H]dihydroalprenolol
K. H. Muntz, T. A. Calianos, D. T. Vandermolen, J. T. Willerson and L. M. Buja
We performed quantitative light microscopic autoradiography of
[3H]dihydroalprenolol (DHA) binding to frozen sections of canine myocardium
to test the hypothesis that there are differences in the density or
affinity of beta-adrenergic receptors on various tissue compartments. In
one study, with concentrations of [3H]DHA from 0.34 to 5.1 nM, specific
binding to cardiac myocytes was saturable, whereas nonspecific binding was
linear with ligand concentration. Arterioles had more specific grain counts
than muscle cells (P less than 0.0001), and Scatchard analysis showed that
the arterioles had a much higher affinity for [3H]DHA than myocytes. In a
second study with lower concentrations of [3H]DHA (0.19-1.98 nM), binding
to the arterioles saturated, whereas binding to the cardiac myocytes did
not. Specific binding to arterioles was significantly higher (P less than
0.0001) than binding to myocytes at all concentrations of [3H]DHA. The
dissociation constants for the subendocardial and subepicardial myocytes
were 1.57 and 1.71 nM, respectively, while the dissociation constant for
the arterioles was 0.26 nM. The maximum number of binding sites was 911
grains/0.9 X 10(-2) mm2 for subepicardial myocytes, 936 for subendocardial
myocytes, and 986 for arterioles. The large nerves accompanying an
epicardial artery also demonstrated specific [3H]DHA binding. Thus this
study has demonstrated major differences in the distribution and affinity
of beta-adrenergic receptors, which may help to explain various
physiological responses to beta-adrenergic stimulation.
