TY - JOUR
T1 - Electrophysiological and receptor binding studies to assess activation of the cardiac adenosine receptor by adenine nucleotides
AU - Ragazzi, E.
AU - Wu, S. N.
AU - Shryock, J.
AU - Belardinelli, L.
PY - 1991
Y1 - 1991
N2 - Adenosine and adenine nucleotides shorten the action potential duration of atrial myocytes and activate a specific acetylcholine adenosine receptor-operated potassium outward current referred to as I(KACh,Ado). The objective of this study was to determine whether adenine nucleotides shorten the action potential duration and increase I(KACh,Ado) in guinea pig atrial myocytes by directly activating adenosine receptors. The potency and efficacy of AMP and adenosine in increasing I(KACh,Ado) and shortening atrial action potential duration were similar; the EC50 values for AMP and adenosine were 3.4 ± 0.8 and 3.1 ± 0.4 μM, respectively. Likewise, the maximum increases in I(KACh,Ado) caused by AMP and adenosine were similar (122 ± 11% versus 123 ± 9%). In comparison, ATP and the stable analogue of AMP, adenosine monophosphorothioate (AMPS), were significantly less potent and efficacious than adenosine and AMP, and inosine had no effect. The electrophysiological effects of AMP were antagonized by the adenosine receptor antagonist 8-(p-sulfophenyl) theophylline and abolished in the presence of adenosine deaminase and α,β-methylene-ADP (APCP, an inhibitor of AMP degradation). Binding of the A1-adenosine antagonist [3H]8-cyclopentyl-1,3-dipropylxanthine (DPCPX) to guinea pig atrial membranes treated with adenosine deaminase and APCP was reduced up to 60% by 100 μM concentrations of AMP, AMPS, and adenosine. Inosine inhibited binding by 43 ± 3% at 100 μM, whereas hypoxanthine and xanthine had little (5-10% inhibition) and uric acid had no effect. Only 3% of AMP and 35% of AMPS were recovered intact after a 90-minute incubation at 21°C with preparations of guinea pig atrial membranes. Percent displacement of [3H] DPCPX binding to atrial membranes by 100 μM AMP was significantly less in the presence of nucleoside phosphorylase and xanthine oxidase (to degrade inosine, hypoxanthine, and xanthine to uric acid) than in their absence (12.4 ± 3.1% versus 49.7 ± 1.5%). The results suggest that the observed electrophysiological actions of adenine nucleotides in cardiomyocytes are mediated by adenosine and are consistent with activation of A1-adenosine receptors.
AB - Adenosine and adenine nucleotides shorten the action potential duration of atrial myocytes and activate a specific acetylcholine adenosine receptor-operated potassium outward current referred to as I(KACh,Ado). The objective of this study was to determine whether adenine nucleotides shorten the action potential duration and increase I(KACh,Ado) in guinea pig atrial myocytes by directly activating adenosine receptors. The potency and efficacy of AMP and adenosine in increasing I(KACh,Ado) and shortening atrial action potential duration were similar; the EC50 values for AMP and adenosine were 3.4 ± 0.8 and 3.1 ± 0.4 μM, respectively. Likewise, the maximum increases in I(KACh,Ado) caused by AMP and adenosine were similar (122 ± 11% versus 123 ± 9%). In comparison, ATP and the stable analogue of AMP, adenosine monophosphorothioate (AMPS), were significantly less potent and efficacious than adenosine and AMP, and inosine had no effect. The electrophysiological effects of AMP were antagonized by the adenosine receptor antagonist 8-(p-sulfophenyl) theophylline and abolished in the presence of adenosine deaminase and α,β-methylene-ADP (APCP, an inhibitor of AMP degradation). Binding of the A1-adenosine antagonist [3H]8-cyclopentyl-1,3-dipropylxanthine (DPCPX) to guinea pig atrial membranes treated with adenosine deaminase and APCP was reduced up to 60% by 100 μM concentrations of AMP, AMPS, and adenosine. Inosine inhibited binding by 43 ± 3% at 100 μM, whereas hypoxanthine and xanthine had little (5-10% inhibition) and uric acid had no effect. Only 3% of AMP and 35% of AMPS were recovered intact after a 90-minute incubation at 21°C with preparations of guinea pig atrial membranes. Percent displacement of [3H] DPCPX binding to atrial membranes by 100 μM AMP was significantly less in the presence of nucleoside phosphorylase and xanthine oxidase (to degrade inosine, hypoxanthine, and xanthine to uric acid) than in their absence (12.4 ± 3.1% versus 49.7 ± 1.5%). The results suggest that the observed electrophysiological actions of adenine nucleotides in cardiomyocytes are mediated by adenosine and are consistent with activation of A1-adenosine receptors.
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U2 - 10.1161/01.RES.68.4.1035
DO - 10.1161/01.RES.68.4.1035
M3 - Article
C2 - 2009606
AN - SCOPUS:0026085599
SN - 0009-7330
VL - 68
SP - 1035
EP - 1044
JO - Circulation Research
JF - Circulation Research
IS - 4
ER -