Final answer:
Pericytes that were growth-arrested would be in the interphase or Go phase of the cell cycle, which is a period where cells are not dividing but can perform normal metabolic activities and prepare for potential future division.
Step-by-step explanation:
If pericytes were growth-arrested so that they would not divide, but other metabolic processes would function normally, the phase of the cell cycle they were in is the interphase. During the interphase, cells are not actively dividing but are involved in other important cellular activities such as growth, DNA replication, and preparation for cell division. It consists of three subphases: G1, S, and G2. Given that the cells are arrested in a state where division does not occur, it is also possible that they are in the Go phase, which is a state outside of the active cell cycle, where cells are quiescent and not preparing to divide.
The fact that cells could be labeled after 4 hours but not after 20 hours indicates that the cell cycle was halted during interphase, since by 20 hours, all labeled cells were in interphase, which suggests that cells did not proceed to mitosis. The Go phase is often a temporary stage due to environmental conditions or a lack of growth signals; however, some cells can also enter Go permanently.