Persistent activation by and receptor reserve for an irreversible A1-adenosine receptor agonist in DDT1 MF-2 cells and in guinea pig heart.
The p- and m-isothiocyanate adenosine derivatives N6-[4-[[[4-[[[[2-[[[(p-(m)-isothiocyanatophenyl)amino]thiocarbonyl ]am ino]ethyl]amino]carbonyl]methyl]anilino]carbonyl]methyl]phenyl] adenosine (p- and m-DITC-ADAC) were examined for irreversible agonist effects at the A1-adenosine receptor (A1-AdoR) in DDT1 MF-2 (DDT) cells and a functional A1-AdoR response in the guinea pig isolated heart. The p- and m-DITC-ADAC inhibited (-)-isoproterenol stimulated cAMP accumulation in DDT cells in the low nanomolar range, and the maximal responses elicited by both compounds were similar to that for N6-cyclopentyladenosine. Once established, the p-DITC-ADAC-mediated inhibition of cAMP accumulation in DDT cells was not affected by the addition of the AdoR antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX). Pretreatment of DDT cells with p-DITC-ADAC (1 microM), followed by washing, reduced [3H]CPX binding to the A1-AdoR by 44% without altering the Kd value for the radioligand to the remaining receptors. The relationship between irreversible A1-AdoR occupancy by p-DITC-ADAC and inhibition of cAMP accumulation revealed a relatively large receptor reserve (64%) for the maximal response. In guinea pig isolated hearts, m-DITC-ADAC (5 microM) prolonged the stimulus to His bundle (SH) interval by 2.1-fold; this response could be prevented by the antagonist 8-cyclopentyltheophylline (5 microM). However, after the SH interval prolongation was established, extensive washout or the addition of 8-cyclopentyltheophylline had little reversal effect on the m-DITC-ADAC response. Binding of [3H]CPX to the guinea pig ventricular membranes after m-DITC-ADAC treatment and washing was reduced by 35%. The A1-AdoR occupancy response relationship for m-DITC-ADAC to prolong the SH interval indicated a small (10-20%) receptor reserve. Both p -and m-DITC-ADAC seem to be irreversible full agonists at the A1-AdoR and may prove to be useful probes to further investigate A1-AdoR structure-function relationships.
Zhang
J
J
Department of Pharmacology, University of Florida, Gainesville, Florida 32610, USA.
Belardinelli
L
L
Jacobson
K A
KA
Otero
D H
DH
Baker
S P
SP
D000241:Adenosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001283:Atrioventricular Node / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects / Q000648:ultrastructure; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure*; D009431:Neural Conduction / Q000187:drug effects; D058906:Purinergic P1 Receptor Agonists; D018047:Receptors, Purinergic P1 / Q000378:metabolism / Q000502:physiology; D014649:Vas Deferens / Q000187:drug effects / Q000648:ultrastructure
C108179:N6-(4-(((4-((((2-((((isothiocyanatophenyl)amino)thiocarbonyl)amino)ethyl)amino)carbonyl)methyl)anilino)carbonyl)methyl)phenyl)adenosine; D058906:Purinergic P1 Receptor Agonists; D018047:Receptors, Purinergic P1; D000242:Cyclic AMP; D000241:Adenosine