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Characterization of adenosine receptors in guinea‐pig isolated left atria
Author(s) -
Jahnel Ulrich,
Nawrath Hermann
Publication year - 1989
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1989.tb12577.x
Subject(s) - adenosine , adenosine receptor , medicine , endocrinology , chemistry , adenosine receptor antagonist , caffeine , purinergic receptor , biology , pharmacology , receptor , agonist
1 The effects of purinergic stimulation on action potential, force of contraction, 86 Rb efflux and 45 Ca uptake were investigated in guinea‐pig left atria. 2 Adenosine exerted a negative inotropic effect which was antagonized by adenosine deaminase but enhanced by dipyridamole. 3 The negative inotropic effect of adenosine was mimicked by 5′‐(N‐ethyl)‐carboxamido‐adenosine (NECA) and the isomers of N 6 ‐(phenyl‐isopropyl)‐adenosine, R‐PIA and S‐PIA. NECA and R‐PIA were about 1000 times more potent than adenosine, whereas R‐PIA was about 100 times more potent than S‐PIA. 4 The inotropic effects of adenosine (in the presence of dipyridamole), NECA, R‐PIA and S‐PIA were competitively antagonized either by theophylline (pA 2 about 4.5) or 8‐phenyltheophylline (pA 2 about 6.3). 5 NECA and R‐PIA shortened the action potential duration and increased the rate constant of the efflux of 86 Rb in a concentration‐dependent manner with no differences in potency; the effects were competitively antagonized by 8‐phenyltheophylline. 6 Barium ions reduced the efflux of 86 Rb under control conditions and antagonized the increase induced by NECA and R‐PIA. 7 NECA and R‐PIA significantly reduced 45 Ca uptake in beating preparations. 8 It is concluded that adenosine, NECA and R‐PIA activate a common receptor population (P 1 or A 3 ) on the outside of the cell membrane of atrial heart muscle to increase the potassium conductance and to reduce the action potential and, thereby, calcium influx and force of contraction.