Adenosine production and release by adult rat cardiocytes

We have examined adenosine (ADO) production and transport in a preparation of isolated adult cardiocytes which attach to and form a monolayer on culture dishes. This preparation contains 85% viable cells which are greater than 50% rod shaped and maintain an ATP/ADP ratio of nine. Incubation under control conditions for 15 mins results in a net release of 240 +/- 47 pmol ADO/mg protein (final adenosine concentration in the medium = 47 +/- 9 nM). Both 0.1 mM dinitrophenol (DNP) and 10 mM iodoacetate (IAA) cause a significant increase in ADO (DNP = 1763 +/- 147 and IAA = 612 +/- 90 pmol/mg). Both 20 microM nitrobenzylthioinosine (NBMPR), an inhibitor of the purine nucleoside carrier, and 0.1 mM alpha,beta-methylene adenosine diphosphate (AOPCP), an inhibitor of 5'-nucleotidase activity, attenuate DNP-stimulated ADO release (NBMPR by 62% and ADOCP by 76%). The results are consistent with the hypothesis that under the conditions of our experiments, adenosine is formed by a 5'-nucleotidase in association with transport across the cell membrane, perhaps by an enzyme-carrier complex. In addition, we have examined the effect of 0.1 mM dipyridamole on the extracellular appearance of adenosine in this preparation and found that it causes a significant increase in the amount of adenosine released. These results are consistent with the hypothesis that dipyridamole inhibits adenosine's uptake more than its release in cardiac myocytes.