Effects of adenosine analogues on contractile response and cAMP content in guinea-pig isolated ventricular myocytes.
In the present study the effects of adenosine analogues were investigated on cAMP content and contractile response in guinea-pig ventricular myocytes. The adenosine analogues (-)-N6-phenylisopropyladenosine (R-PIA), 5'-N-ethylcarboxamideadenosine (NECA) and (+)-N6-phenylisopropyladenosine (S-PIA) in the presence of 0.01 mumol/l isoprenaline reduced contractile response concentration-dependently. R-PIA and NECA were about equipotent (IC25: 0.01 mumol/l and 0.039 mumol/l respectively), while S-PIA was less potent (IC25: 0.6 mumol/l). Isoprenaline stimulated cAMP content was reduced by R-PIA (IC25: 0.004 mumol/l) and with lower potency by S-PIA (IC25: 0.15 mumol/l), but the extent of reduction of cAMP by R-PIA and S-PIA (to 55% and 64% respectively) was less than the reduction of contractile response (to 26% and 55% respectively). This suggests that the effects of R- and S-PIA on contractile response are only in part due to a reduction in cAMP content. In addition, NECA did not decrease cAMP content but decreased contractile response to the same extent as R-PIA. Similar results were obtained in the presence of the phosphodiesterase inhibitor Ro 20-1724. Time course studies revealed that the effects of R-PIA (1 mumol/l) on cAMP content and contractile response coincided reaching steady state after 5 min and remained stable thereafter. The effects of NECA (1 mumol/l) on contractility also reached steady state within 5 min, whereas it did not change cAMP content. It is concluded that the reduction of contractility by adenosine analogues in the presence of isoprenaline can only in part be explained by a reduction of cAMP content.(ABSTRACT TRUNCATED AT 250 WORDS)
Neumann
J
J
Abteilung Allgemeine Pharmakologie, Universitäts-Krankenhaus Eppendorf, Universität Hamburg, Federal Republic of Germany.
Schmitz
W
W
Scholz
H
H
Stein
B
B
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D004558:Electric Stimulation; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*
D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone; D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D000241:Adenosine; D007545:Isoproterenol