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Am J Physiol Heart Circ Physiol 257: H162-H169, 1989;
0363-6135/89 $5.00
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AJP - Heart and Circulatory Physiology, Vol 257, Issue 1 162-H169, Copyright © 1989 by American Physiological Society

ARTICLES

Distribution of alpha 1-adrenergic receptors in myocytic regions and vasculature of feline myocardium

J. E. Saffitz
Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110.

The physiological and pathophysiological roles of myocardial alpha 1-adrenergic receptors are not clearly defined. To delineate the distribution of alpha 1-receptors in myocytic and vascular components of the heart, we characterized the binding of [3H]prazosin to alpha 1-receptors in unfixed, transmural slices of feline left ventricle. Specific binding ratios greater than 95% were achieved at radioligand concentrations near the dissociation constant (Kd). Binding of radioligand to receptors in transmural slices was rapid, reversible, saturable, stereoselective, and displaceable by subtype-selective antagonists with a rank order of potency characteristic of alpha 1-receptors. Analysis of binding isotherms indicated a Bmax of 9.1 +/- 1.9 fmol/mg protein and a Kd of 36.9 +/- 6.3 pM. Results of light microscopic autoradiography indicated that regions composed of closely arranged cardiac myocytes contained three to fourfold more alpha 1-receptors per unit section area than the resistance microvasculature, which in turn contained approximately twice the density of alpha 1-receptors observed in the medial smooth muscle of large conductance arteries. No differences in the density of alpha 1-receptors between subepicardial and subendocardial regions were observed for either myocytic regions or coronary arterioles. These results indicate that myocytic regions of the cat ventricle contain a high density of alpha 1-adrenergic receptors. The methods developed should be of value in characterizing the distribution and function of alpha 1-receptors and mechanisms of regulation of adrenergic responsiveness in intact myocyardium.


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 Am. J. Physiol. Heart Circ. Physiol.Home page
D. V. DeFily, Y. Nishikawa, and W. M. Chilian
Endothelin antagonists block alpha 1-adrenergic constriction of coronary arterioles
Am J Physiol Heart Circ Physiol, March 1, 1999; 276(3): H1028 - H1034.
[Abstract] [Full Text] [PDF]


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