colorectal cell culture - (Feb/23/2015 )

Hey guys.

I am a masters student performing cell culture for the first time.I am working with colorectal cancer cell lines(HT29 and sw480) and breast cancer cell line MCF-7.This is the 4th  week since I cultured the cells.I used passaged cells from my colleague.HT29-P no165,SW480-Passage no 178 and MCF-7 P no 11.The cells are growing fine.My problem is, inconsistency in number of days of incubation I split my cells.i.e the 1st week of culture I split them after 6 days and the confluency was 90%,2nd week after 7days of incubation confluency was about 90%..with the MCF-7 I split after 7,8 and 7 days because I looked at the confluency.My question is does the time of incubation  really matter or the confluency of the cells is the one that I should consider.?

Thanks..

Confluency is the key - ideally you should passage your cells so that they remain in an actively growing state. Once cells get too confluent (over 70-80%) they start to grow more slowly due to contact inhibition (if they are contact inhibited) and create cell:cell networks that can be hard to split apart. It also means that the cells grow in 3D structure rather than as a mono-layer, which is what you are aiming for. This isn't to say that they won't grow when too confluent (some lines will stop though), but that it is best if you keep them passaged fairly frequently. Waiting a defined time is not a good idea as this will easily lead to depletion of nutrients (you should be changing the medium every 2-5 days or when passaging) and overgrowth...

ok got it.Thanks