For SEM 1 mM ATP was added to CHME-5 cells sparsely grown on 10-mm glass coverslips; the fixation step was performed with a solution composed by 4% paraformaldheyde-2% glutaraldheyde (in PBS) at RT. Samples were post-fixed in 1% OsO4, dehydrated in ethanol, critical-point dried and sputter-coated with gold palladium for 50 s. Images were collected with a Leica S420 scanning electron microscope.