Characteristics of spontaneous Ca2+ oscillations in bovine aortic endothelial cells in Ca2+-free solution

In nominally Ca2+-free solution, the incidence of spontaneous Ca2+ oscillations in the cultured bovine aortic endothelial (BAE) cells may occur during superfusion. Application of 3 microM ATP induced a single Ca2+ transient regardless of the prior absence or presence of spontaneous oscillations. The total mobilized [Ca2+] depends on the incidence of spontaneous oscillations and the length of exposure in Ca2+-free solution. The maximal rate of rise of the transient in cells induced by ATP immediately after an spontaneous spike was greater than that in cells without any spontaneous activity. But there was no difference in the recovery time constant. The sum of areas of spontaneous and ATP-induced transients in cells with spontaneous activity was not different from that of ATP-induced transient in cells without spontaneous activity. The results suggest that BAE cells, after growth to confluence, are subjected to spontaneous oscillations during superfusion in Ca2+-free solution. The release of internal Ca2+ in response to ATP is enhanced in cells with spontaneous oscillations. The content of ATP-sensitive stores continually decreased when cells were superfused with Ca2+-free solution, and most of the spontaneous release of Ca2+ was lost and not sequestrated back into ATP-sensitive stores.