Effect of α2-adrenoceptor stimulation on isolated canine purkinje fiber contraction

Roberta S. Stephenson, John J. Cai, Thomas A. Drews, Hon Chi Lee

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

We have recently identified the presence of postjunctional α2- adrenoceptors in canine Purkinje fibers. In this study, we examined the effects of α2-adrenoceptor stimulation on the contraction strength of isolated Purkinje fibers. Exposure to the α2-adrenoceptor specific agonist and antagonist, UK 14,304 (5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6- quinoxalinamine) and yohimbine (17-hydroxyyohimban-16-carboxylic acid methyl ester hydrochloride) alone at 0.1 μM respectively, did not produce any significant effect on Purkinje contraction strength. Purkinje contraction strength was augmented by isoproterenol (0.1 μM), forskolin (0.1 μM), or 8- bromo-adenosine cyclic 2',3'-monophosphate (8-bromo-cAMP, 10 μM). UK 14,304 significantly reversed the effects of isoproterenol and forskolin but not those of 8-bromo-cAMP on Purkinje contraction strength. After incubation with pertussis toxin, the positive inotropic effect of forskolin on Purkinje contraction strength remained intact, but the forskolin effect could no longer be reversed by UK 14,304. These results suggest that the postjunctional α2-adrenoceptors in canine Purkinje fibers are coupled to a pertussis toxin-sensitive G protein, probably G(i). Stimulation of the α2- adrenoceptor antagonizes the effect of β-adrenoceptor stimulation on Purkinje contraction strength in an accentuated antagonism manner.

Original languageEnglish (US)
Pages (from-to)261-267
Number of pages7
JournalEuropean Journal of Pharmacology
Volume345
Issue number3
DOIs
StatePublished - Mar 26 1998

Keywords

  • Antagonism accentuated
  • Contraction strength
  • Pertussis toxin
  • Purkinje fiber
  • UK 14,304
  • α-Adrenoceptor

ASJC Scopus subject areas

  • Pharmacology

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