EFFECT OF 5'-DEOXY-5'-ISOBUTYLTHIOADENOSINE ON FORMATION AND RELEASE OF ADENOSINE FROM NEONATAL AND ADULT-RAT VENTRICULAR MYOCYTES

1. Studies in rat polymorphonuclear leucocytes have suggested that 5'- deoxy-5'-isobutylthioadenosine (IBTA), an inhibitor of the IMP-selecti ve cytosolic 5'-nucleotidase, may be used to test its role in adenosin e formation in intact cells. We investigated adenosine formation in ne onatal and adult rat cardiomyocytes. 2. 2-Deoxyglucose (30 mM) with ol igomycin (2 mug/ml) induced a 90-100% fall in ATP concentration in 10 min in neonatal and 60 min in adult heart cells. Adenosine accumulatio n was substantially increased, accounting for 13% of the fall in ATP c oncentration in neonatal cells and 56% in adult cells. 3. Anti-(rat li ver ecto-5'-nucleotidase) serum did not inhibit adenosine accumulation . Furthermore, dipyridamole (10 muM), a nucleoside-transport blocker, inhibited by 80% the appearance of the newly formed adenosine in the m edium, showing that adenosine is produced intracellularly by both adul t and neonatal-rat myocytes in response to inhibition of oxidative met abolism. 4. IBTA (3 mM) inhibited by 80% the appearance of adenosine i n the medium, but did not inhibit total adenosine accumulation by neon atal-rat myocytes and only modestly inhibited total adenosine accumula tion by adult myocytes. 5. IBTA, like dipyridamole, inhibited incorpor ation of extracellular adenosine (10 muM) into neonatal and adult vent ricular myocyte nucleotides by 60-70%. Transport of IBTA (100 muM) int o the cells did not appear to be inhibited by dipyridamole (30 muM). 6 . We conclude that IBTA acted primarily to inhibit adenosine release f rom myocytes. The small effect on adenosine formation rates implies th at the IMP-selective cytosolic 5'-nucleotidase plays a minor role in t his tissue.