Ca²⁺ signalling is a crucial form of both inter-and intracellular signalling in the vascular endothelium. We have previously shown that such signalling is dramatically altered by periods of chronic hypoxia in other cell types (e.g. Smith et al. 2003). Here, we have investigated the effects of chronic hypoxia (2.5 % O₂, 24h) on agonist-evoked changes of [Ca²⁺]_i in human vascular endothelial cells. We also compare responses from arterial (internal mammary artery) and venous (saphenous vein) vessels. Cells were isolated and maintained in primary culture as previously described (Budd et al. 1991), and [Ca²⁺]_i monitored in Fura-2 loaded cells (see Smith et al. 2003, for details). Tissue was obtained with Local Ethical Permission and informed consent.

Bath application of a supramaximal concentration of ATP (10 µM) in a Ca²⁺-free perfusate (containing 1 mM EGTA) evoked transient rises of [Ca²⁺]_i that were significantly larger (P < 0.01, unpaired Student’s t test) in arterial cells (0.208 ± 0.008 ratio units (r.u.), mean ± S.E.M., n = 54 cells) than venous cells (0.172 ± 0.006 r.u., n = 41). Chronic hypoxia significantly potentiated peak responses in arterial cells (to 0.246 ± 0.009 r.u., n = 54, P < 0.01). However, responses in venous cells were unchanged at 0.187 ± 0.007 r.u. (n = 35).

Following 10 min exposure of cells to thapsigargin (1 µM), ATP failed to evoke rises of [Ca²⁺]_i when the perfusate was Ca²⁺-free. Re-admission of 2.5 mM Ca²⁺ to the perfusate caused rises of [Ca²⁺]_i presumably due to capacitative Ca²⁺ entry (CCE). CCE was significantly greater (P < 0.01) in arterial cells (e.g. 0.210 ± 0.013 r.u. at 120 s after Ca²⁺ re-admission, n = 46) than in venous cells (0.124 ± 0.008 r.u., n = 40). Chronic hypoxia did not alter CCE in arterial cells, but significantly increased CCE (P < 0.01) in venous cells.

Our results indicate that ATP-evoked Ca²⁺ signalling appears quantitatively different in human arterial endothelial cells as compared with venous cells. Furthermore, evidence for remodelling of such signalling by chronic hypoxia was found in both cell types. These observations have important implications for perpetuation or genesis of hypoxia-inducible cardiovascular events.

This work was supported by the British Heart Foundation and Pfizer Central Research