Effect of temperature on atrial and ventricular adenosine A1 receptors of the guinea pig.
Cardiac adenosine receptors are coupled to adenylate cyclase inhibition. In the guinea pig heart, the relative agonist potencies observed for adenylate cyclase inhibition were R-N6-phenylisopropyladenosine (R-PIA) = N6-cyclohexyladenosine greater than 5'-N-ethylcarboxamidoadenosine much greater than S-PIA. In both atrial and ventricular membranes, the antagonists 8-phenyltheophylline (8-PT) and isobutylmethylxanthine (IBMX) also showed similar affinities for atrial and ventricular adenosine receptors. The same pattern of relative agonist potencies was observed in experiments performed at either 25 or 37 degrees C. However, the maximal inhibition produced by R-PIA in atrial membranes decreased from 30.8 +/- 3.2% (n = 7) at 25 degrees C to 18.8 +/- 1.6% (n = 4) at 37 degrees C. No such difference in maximal inhibition was observed with ventricular membranes at these two temperatures (34.5 +/- 1.6%, n = 6 at 25 degrees C and 35.3 +/- 0.9%, n = 11 at 37 degrees C). While there was no change in agonist potencies, the affinities of the antagonists 8-PT and IBMX at cardiac adenosine A1 receptors were affected by temperature. At 25 degrees C, the pKD values for 8-PT and IBMX in ventricular membranes were 4.65 +/- 0.21 (n = 3) and 4.55 +/- 0.20 (n = 3), respectively. Their affinities were 7- to 19-fold higher at 37 degrees C, the pKD values being 5.93 +/- 0.12 (n = 7) (p less than 0.02) and 5.38 +/- 0.18 (n = 3) (p less than 0.05), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D006168:Guinea Pigs; D006325:Heart Atria / Q000378:metabolism; D006352:Heart Ventricles / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D011983:Receptors, Purinergic / Q000187:drug effects / Q000378:metabolism*; D013696:Temperature; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology
D000067956:Adenylyl Cyclase Inhibitors; D011983:Receptors, Purinergic; D013806:Theophylline; C028322:8-phenyltheophylline; D000241:Adenosine; D015056:1-Methyl-3-isobutylxanthine