Evidence for deactivation of both ectosolic and cytosolic 5'-nucleotidase by adenosine A1 receptor activation in the rat cardiomyocytes.
Adenosine, an important regulator of many cardiac functions, is produced by ectosolic and cytosolic 5'-nucleotidase. The activity of these enzymes is influenced by several ischemia-sensitive metabolic factors, e.g., ATP, ADP, H+, and inorganic phosphate. However, there is no clear evidence that adenosine itself affects 5'-nucleotidase activity. This study tested whether adenosine decreases the activity of ectosolic and cytosolic 5'-nucleotidase. Cardiomyocytes were isolated from adult male Wistar rats and suspended in the modified Hepes-Tyrode buffer solution. After stabilization, isolated cardiomyocytes were incubated with and without adenosine (10(-9) - 10(-4) M). Ectosolic and cytosolic 5'-nucleotidase activity was decreased by exogenous adenosine (ectosolic 5'-nucleotidase activity, 20.6 +/- 2.3 vs. 8.6 +/- 1.6 mumol/min per 10(6) cells [P < 0.05]; cytosolic 5'-nucleotidase activity, 2.47 +/- 0.58 vs. 1.61 +/- 0.54 mumol/min per 10(6) cells [P < 0.05] at 10(-6) M adenosine) after 30 min. The decrease in ectosolic and cytosolic 5'-nucleotidase activity was inhibited by 8-phenyltheophylline and pertussis toxin, and was mimicked by N6-cyclohexyladenosine, an adenosine A1 receptor agonist. Neither CGS21680C, and A2 receptor agonist, nor cycloheximide deactivated ectosolic and cytosolic 5'-nucleotidase. Thus, we conclude that activation of adenosine A1 receptors is coupled to Gi proteins and attenuates ectosolic and cytosolic 5'-nucleotidase activity in rat cardiomyocytes.
Kitakaze
M
M
First Department of Medicine, Osaka University School of Medicine, Japan.
Hori
M
M
Minamino
T
T
Takashima
S
S
Komamura
K
K
Node
K
K
Kurihara
T
T
Morioka
T
T
Sato
H
H
Inoue
M
M
D015720:5'-Nucleotidase / Q000378:metabolism*; D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D002451:Cell Compartmentation; D002469:Cell Separation; D000242:Cyclic AMP / Q000032:analysis; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000187:drug effects; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D037342:Pertussis Toxin; D051381:Rats; D017208:Rats, Wistar; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D015398:Signal Transduction; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D018047:Receptors, Purinergic P1; D010566:Virulence Factors, Bordetella; D013806:Theophylline; D000242:Cyclic AMP; C028322:8-phenyltheophylline; D037342:Pertussis Toxin; D015720:5'-Nucleotidase; D000241:Adenosine