EXTRACELLULAR ADENOSINE 5'-TRIPHOSPHATE INDUCES CA2-RAT CARDIOMYOCYTES - POSSIBLE INVOLVEMENT OF NA+( EFFLUX FROM FRESHLY ISOLATED ADULT)CA2+ EXCHANGE MECHANISM/

In the present study, we examined the effect of extracellular adenosin e 5'-triphosphate (ATP) on Ca2+ efflux from freshly isolated adult rat cardiomyocytes. ATP at 1 mM caused a release of 3.6+/-0.08% of the to tal cellular content. The Ca-45(2+) efflux from the cells was also sti mulated by adenosine-5'-O-(3-thiotriphosphate) (ATP-gamma s), alpha,be ta-methylene-ATP and adenosine 5'-diphosphate (ADP), but not by adenos ine 5'-monophosphate (AMP) or adenosine. The effect of ATP was inhibit ed by a known purinergic P-2-receptor antagonist, but not by a P-1-rec eptor antagonist. From these results, it is conceivable that the effec t of ATP on Ca2+ efflux from cardiomyocytes is mediated through P-2-pu rinoceptars. It was also observed that ATP caused a rise in [Ca2+](i) to almost 200 nM. The ATP-stimulated Ca-45(2+) efflux was not affected by removal of extracellular Ca2+, but was dependent on the presence o f extracellular Na+. Moreover, ATP caused a Na-22(+) influx into the c ells of about 2.0-fold over the basal value. These results suggest tha t ATP stimulates extracellular Na+-dependent Ca-45(2+) efflux from fre shly isolated adult rat cardiomyocytes, probably through its stimulato ry effect on plasma membrane P-2-purinoceptors which may couple to Na/Ca2+ exchange.