ENDOTHELIN-1 RELEASE BY ERYTHROPOIETIN INVOLVES CALCIUM SIGNALING IN ENDOTHELIAL-CELLS

We investigated the effects of recombinant human erythropoietin (rHuEP O) on intracellular calcium ([Ca2+](i)) and whether these changes regu late both endothelin-l (ET-1) protein release and ET-1 messenger RNA ( mRNA) production in bovine pulmonary arterial endothelial cells (BPAEC ). rHuEPO (3.3 U/ml) induced [Ca2+](i) increases from a basal level of 54 +/- 12.2 (SE) to 147 +/- 21.1 nM (p < 0.001), in fura-2-loaded BPA EC. In the presence of nifedipine (10 mu M), the increases in [Ca2+](i ) were significantly reduced. Furthermore, when extracellular calcium ([Ca2+](o)) was reduced (200 mu M), there was a significant reduction in [Ca2+](i) increase after stimulation with rHuEPO. Incubation of BPA EC with rHuEPO for 4 h increased ET-1 levels in the culture supernatan t from 44.7 +/- 5.3 to 85 +/- 7.6 pg/ml (p < 0.001). However, when the cells were treated with rHuEPO and nifedipine, the ET-1 levels were d ecreased, as compared to levels resulting from treatment with rHuEPO a lone (41 +/- 6.1 vs. 85 +/- 7.6 pg/ml, p < 0.001, respectively). rHuEP O also induced a fourfold increase in the level of the preproET-1 mRNA as compared with control. PreproET-1 mRNA was diminished in the prese nce of nifedipine and rHuEPO and rHuEPO can increase [Ca2+](i) in BPAE C, and this increase may be related to the stimulation of ET-1 synthes is and release.