The mechanism of agonist induced Ca2+ signalling in intact endothelial cells studied confocally in in situ arteries

In agreement with previous work, carbachol stimulated a rise in intracellular Ca2+ in the endothelial cells, consisting of a rapid initial phase, then a plateau upon which oscillations of Ca2+ were superimposed, followed by a decline to basal Ca2+ levels upon carbachol removal. Our data support the following conclusions: (i) the size (amplitude and duration) of the Ca2+ spike and early oscillations are limited by SERCA activity, thus both are increased if SERCA is inhibited. (ii) SERCA activity is such that brief applications of carbachol do not trigger CCE, presumably because the fall in luminal Ca2+ is not sufficient to trigger it. However, longer applications sufficient to deplete the ER or even partial SERCA inhibition stimulate CCE. (iii) Ca2+ entry occurs via STIM-mediated CCE and SERCA contributes to the cessation of CCE. In conclusion our data show how SERCA function is crucial to shaping endothelial cell Ca signals and its dynamic interplay with both CCE and ER Ca releases.