Fig. 1. UTP elicits asynchronous calcium oscillations in HeLa cells. (Top) Monolayers of HeLa cells were loaded with the calcium indicator fura-2 and 1 µM UTP was added to the medium while ratio imaging was performed. Time after UTP exposure is indicated on each panel. Scale bar: 40 µm. Oscillating cells (as detected in the bottom panel) are marked with an asterisk. (Bottom) Graph of cytosolic calcium concentration over time for single HeLa cells as shown in the top panel. An initial rise in cytosolic calcium was followed by random, asynchronous calcium oscillations in most cells.