Should imaging media formulation match growth media? - (Jul/21/2014 )

I am culturing a HeLa cell line in RPMI 1640 medium, no HEPES.  Normally when I do live cell imaging on a confocal microscope I replace the growth medium with an imaging buffer which is essentially just MEM+Serum+HEPES.  I use this just because I was taught to use this when I started in my current lab, and it is convenient because there is a core here that sells that buffer.  However, I was wondering if I should actually make up an imaging buffer using RPMI without phenol red, and with the addition of HEPES.  

The cells are usually in the imaging buffer for anywhere from 30 minutes to 4 hours.  HEPES is added because the cells are outside of the 5% CO2 incubator during imaging.

tldr;  does the formulation of my imaging buffer need to match the growth media I am using?

Short answer: no

long answer: yes... for short time points, and depending on what you are looking for, having the cells in a different buffer system probably won't affect the result, but for longer time points and specific applications (e.g. macrophage differentiation, interferon stimulation etc.) then changing the medium could have a dramatic effect on the behaviour of the cells.