You will start inhibiting endocytosis in cells near room-temperature (18-19 degrees Celsius). I did the majority of my ligand binding assays at 4 degrees for an hour. None of my experiments have called for treating cells at 4 degrees for more than four hours. I have seen reports of cells successfully being held in adherent and spinner cultures for 9 days at 4 degrees, then returned to exponential growth by raising the temperature to 37 degrees. That temperature resilience may be cell line or even cell-strain dependent.

Article Low‐temperature pausing of cultivated mammalian cells

I can't tell from the provided information what you are trying to do for sure, but DAPI will stain any DNA that it can get to although it is not very cell permeant. If the fluid in endocytic or pinocytic vesicles were one way for DAPI to get into the cell, I would not expect it to get into cells at 4 degrees. If you are looking for a nuclear counterstain, Hoechst 33342 is a lot more cell permeant.

Good luck!

Hi Lucia,

What kind of cells are you working with ?

Plant cells such as BY-2 can stay to 4°C for several hours.

DAPi won't work at any temperature if you haven't permeabilised your cells in some way, but Hoescht is cell permeable. From my experience nuclear dyes will generally work at any temperature but as a general rule if its colder incubate for longer.