ANGIOTENSIN-II AS A STIMULATOR OF NA-DEPENDENT CA2+ EFFLUX FROM FRESHLY ISOLATED ADULT-RAT CARDIOMYOCYTES()

In cardiac tissues, angiotensin II causes inotropic and chronotropic e ffects on the heart. It is indicated that the mechanism of the inotrop ic effect of angiotensin II is attributed to an increase in cytosolic free calcium ([Ca2+](i)) in cardiomyocytes. However, increased [Ca2+]( i) should be restored to a physiological level because cumulative elev ation in [Ca2+](i) leads to irreversible injury in cardiomyocytes. Whe reas it is known that angiotensin II causes the increase in [Ca2+](i) in cardiac cells, little is known about the mechanisms of decrease in [Ca2+](i) in cardiomyocytes upon angiotensin II stimulation. In the pr esent study, we examined the effect of angiotensin II on Ca2+ efflux f rom freshly isolated adult rat cardiomyocytes. Angiotensin II stimulat ed the efflux of Ca-45(2+) from the cells in a concentration dependent manner (10(-7)-10(-5) M). The Ca-45(2+) efflux from the cells was inh ibited by type 1 angiotensin II receptor inhibitor. The angiotensin II -stimulated Ca-45(2+) efflux was not affected by deprivation of the ex tracellular Ca2+, but was dependent on the presence of extracellular N a+. These results indicate that angiotensin II stimulates extracellula r Na+-dependent Ca-45(2+) efflux from freshly isolated adult rat cardi omyocytes, probably through its stimulatory effect on the plasma membr ane type 1 angiotensin II receptors which may couple to Na+/Ca2+ excha nge.