Comparison of muscarinic receptor properties in hatched chick heart atrium and ventricle
We have reported previously that chick myocardium responds to muscarinic agonists with a decrease in slow inward current in both atrial and ventricular muscle. A second ionic current, the background potassium current, is increased in the atrium but not in the ventricle. A possible explanation for th...
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Published in | The Journal of pharmacology and experimental therapeutics Vol. 236; no. 3; pp. 602 - 609 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Bethesda, MD
American Society for Pharmacology and Experimental Therapeutics
01.03.1986
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Subjects | |
Online Access | Get full text |
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Summary: | We have reported previously that chick myocardium responds to muscarinic agonists with a decrease in slow inward current in
both atrial and ventricular muscle. A second ionic current, the background potassium current, is increased in the atrium but
not in the ventricle. A possible explanation for the modulation of potassium current in atrium only is the existence of a
unique muscarinic receptor population in atrium responsible for potassium conductance changes. We looked for differences in
atrial and ventricular muscarinic receptors by pharmacological and biochemical techniques. The dissociation constants for
binding of l-[3H]quinuclidinyl benzilate were 46 pM in both tissues. Estimates for binding of atropine in competitive binding
experiments gave dissociation constants of 1.8 nM in atrium and 2.0 nM in ventricle. Pharmacologic evaluation of atropine
occupancy of muscarinic receptor by Schild analysis showed no difference in the dissociation constants in atrium (1.7 nM)
and ventricle (1.1 nM). Displacement of 0.1 nM [3H]quinuclidinyl benzilate with carbachol showed the atrium to have a higher
apparent affinity for agonist than the ventricle (atrium IC50 = 8.2 X 10(-6) M, ventricle IC50 = 2.1 X 10(-5) M). Computerized
curve fitting analysis detected three binding states (super high, high and low affinity) for carbachol in the atrium and ventricle
in the absence and presence of 5'-guanylylimidodiphosphate (10(-4) M). We did not detect a qualitative difference between
atrial and ventricular muscarinic receptors. Muscarinic-induced potassium conductance changes which occur in the atria do
not appear to be due to a unique muscarinic receptor in atria. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 ObjectType-Article-1 ObjectType-Feature-2 |
ISSN: | 0022-3565 1521-0103 |