Calcium signalling in adult endothelial outgrowth cells.

Endothelial outgrowth cells (EOCs) derived from blood mononuclear cells can differentiate to an endothelial-like phenotype. There are deficits in understanding of the biology of these cells, particularly detailed characterisation of their Ca(2+) signalling mechanisms. In the current study, it was found that human EOCs express two forms of ryanodine receptor (RyR1 and RyR2) Ca(2+) release channel in their endoplasmic reticulum. Individual EOCs display heterogeneous Ca(2+) responses to physiologically relevant regulators fibrinogen and collagen. Some EOCs showed distinctive, multiphasic Ca(2+) responses to fibrinogen consisting of rapid decreases, transient increases then a gradual return to the resting levels. Transient elevations in Ca(2+) required both L-type voltage gated calcium channels and RyRs. Decreases in Ca(2+) stimulated by fibrinogen depended on plasma membrane Ca(2+) ATPase pumps, but did not require thapsigargin-sensitive Ca(2+) ATPases. These results indicate that EOCs possess sophisticated Ca(2+) signalling mechanisms, capable of generating distinct Ca(2+) waveforms in response to different physiologically relevant cues.