Abstract
An increase in intracellular Ca^2+^ concentration ([Ca^2+^]~i~) may play a role in the proliferative effect of several growth factors. In this study, the changes in [Ca^2+^]~i~ elicited by epidermal growth factor (EGF) in rat cardiac microvascular endothelial cells (CMEC) have been investigated by using fura‐2 conventional and confocal microscopy. A large heterogeneity in the latency and in the pattern of the Ca^2+^ response was found at each dose of EGF (2.5–100 ng/ml), whereas some cells displayed a non‐oscillatory behavior and others exhibited a variable number of Ca^2+^ oscillations. On average, the fraction of responsive cells, the total number of oscillations and the duration of the Ca^2+^ signal were higher at around 10 ng/ml EGF, while there was no dose‐dependence in the lag time and in the amplitude of the [Ca^2+^]~i~ increase. EGF‐induced Ca^2+^ spikes were abolished by the tyrosine kinase inhibitor genistein, but not by its inactive analogue daidzein, and by the phospholipase C blocker NCDC. Only 1–2 transients could be elicited in Ca^2+^‐free solution, while re‐addition of extracellular Ca^2+^ recovered the spiking activity. The oscillatory signal was prevented by the SERCA inhibitor thapsigargin and abolished by the calcium entry blockers Ni^2+^ and La^3+^. Moreover, EGF‐induced Ca^2+^ transients were abolished by the InsP~3~ receptor blocker caffeine, while ryanodine was without effect. Confocal imaging microscopy showed that the Ca^2+^ response to EGF was localized both in the cytoplasm and in the nucleus. We suggest that EGF‐induced [Ca^2+^]~i~ increase may play a role in the proliferative action of EGF on endothelial cells. © 2002 Wiley‐Liss, Inc.