EFFECTS OF CORONARY VASODILATOR DRUGS ON THE UPTAKE AND RELEASE OF ADENOSINE IN CARDIAC-CELLS

The effects of coronary vasodilator drugs on the uptake and release of adenosine due to hypoxia were studied in isolated chick embryo cardiac cells maintained in culture. Isolated cardiac cells were used as a model in order to avoid the problems associated with intact heart models, i.e., cellular heterogeneity, and hormonal and neural influence. A Km value of 2.5 .mu.M and a Vmax of 0.9 nmol/mg of protein per 30 min were determined for the uptake of adenosine in this model. The ability of coronary vasodilator drugs to inhibit the uptake of adenosine (0.023 .mu.M) into heart cells was in the order dipyridamole > dilazep > hexobendine > lidoflazine > papaverine. All the agents blocked the uptake of adenosine in a competitive manner. Concentrations ranging from 10-3-10-9 M of aminophylline, carbochromen and nitroglycerin had no effect on the uptake of adenosine into the cardiac cells. No drug had a significant effect on the release of adenosine from the heart cells under hypoxic conditions. Apparently the coronary vasodilator actions of dipyridamole, dilazep, hexobendine, papaverine and lidoflazine are related to an adenosine uptake blockade.