THE EFFECT OF THE CALCIUM-ANTAGONIST NITRENDIPINE ON INTRACELLULAR CALCIUM-CONCENTRATION IN ENDOTHELIAL-CELLS

1 Nitrendipine induces NO-release from coronary vascular endothelium p resumably by activating endothelial NQ-synthase. We have investigated whether this effect may be mediated by an influence on the intracellul ar calcium in endothelial cells. 2 Bovine aortic endothelial cells (BA EC) were incubated with Fura-2/AM (1 mu M) for 30 min and Fura-2 fluor escence was measured at 510 nm in response to chopped excitation with both 340 and 380 nm. The ratio 340/380 nm (known to reflect changes in intracellular calcium) was calculated from these data. 3 Nitrendipine (0.1 to 100 mu M) led to a significant, concentration-dependent, mono phasic increase in [Ca2+](i) in suspended BAEC by 11 +/- 2 nM (0.1 mu M), 23 +/- 3 nM (1 mu M), 34 +/- 4 nM (10 mu M) and by 47 +/- 5 nM (10 0 mu M) from a control level of 118 +/- 10 nM. 4 This elevation of int racellular calcium was prevented by pretreatment of BAECs with gadolin ium (100 mu M) or by incubation with calcium free saline solution. In contrast, the application of 0.3 mu M thapsigargin did not abolish the nitrendipine-induced calcium signal. In additional experiments it was shown that the nitrendipine-induced NO-release (as measured with the oxy-haemoglobin-method could also be inhibited by gadolinium and was a bsent in calcium-free solution. 5 Thus, nitrendipine elevates intracel lular calcium in suspended BAECs in a concentration-dependent manner. This elevation is mainly due to a gadolinium-sensitive calcium influx from the extracellular space rather than a calcium release from intrac ellular stores.