Ca2+ influx was assessed by imaging using Fluo-4AM as a Ca2+ indicator; briefly, CHME-5 cells were washed two times with KRH solution, then incubated in the dark with Fluo-4AM (4 µM in KRH) at room temperature for 45 min. Pluronic acid (20% w/v) was used for keeping Fluo-4AM in solution. Afterward, cells were washed two times in KRH and incubated for 20 min at 37°C for allowing the complete de-esterification of the indicator. After an additional wash in KRH, cells were treated or not with ATP (1 mM) and imaged under an Axiovert A1 microscope (Karl Zeiss). Untreated cells were used as a control for determining the baseline fluorescence of Fura-4AM.