Effect of alpha adrenergic agonists and blockers on Purkinje fiber transmembrane potentials and automaticity in the dog
Previous studies have shown that alpha adrenergic stimulation can reduce the automaticity of canine Purkinje fibers. In the present study, our interest was to determine whether this is an alpha-1 or alpha-2 adrenergic action. We used standard microelectrode techniques to study the effects of the alp...
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Published in | The Journal of pharmacology and experimental therapeutics Vol. 231; no. 3; pp. 566 - 571 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Bethesda, MD
American Society for Pharmacology and Experimental Therapeutics
01.12.1984
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Subjects | |
Online Access | Get full text |
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Summary: | Previous studies have shown that alpha adrenergic stimulation can reduce the automaticity of canine Purkinje fibers. In the
present study, our interest was to determine whether this is an alpha-1 or alpha-2 adrenergic action. We used standard microelectrode
techniques to study the effects of the alpha agonists, phenylephrine and clonidine, and the alpha antagonists, prazosin and
yohimbine, on phenylephrine-induced decreases in automaticity. Prazosin and yohimbine, 1 X 10(-5) M, alone, significantly
reduced the amplitude and upstroke velocity (Vmax) of stimulated action potentials. In addition, yohimbine, 1 X 10(-5) M,
accelerated and prazosin, 1 X 10(-5) M, attenuated repolarization. Prazosin, 1 X 10(-5) M, and yohimbine greater than or equal
to 1 X 10(-7) M, alone, decreased automaticity. Phenylephrine, 5 X 10(-8) M, alone, significantly increased the cycle length
of automatic Purkinje fibers. The effects of phenylephrine on automaticity were blocked by prazosin but not by yohimbine.
Clonidine, alone, 1 X 10(-6) and 1 X 10(-5) M, significantly reduced automaticity, an effect that was not blocked by yohimbine
or prazosin. Clonidine, 1 X 10(-6) and 1 X 10(-5) M, also significantly reduced Vmax and prolonged action potential duration
of driven Purkinje fibers, an action consistent with direct membrane effects. These experiments suggest that the negative
chronotropic effects of phenylephrine on Purkinje fiber automaticity are mediated by alpha-1 adrenergic receptors. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3565 1521-0103 |