Figure 4

Large Schwann cells synthesize and degrade protein faster than smaller cells. (a) Quiescent cells were cultured in 3% FCS, forskolin, and aphidicolin for various times. The rate of protein synthesis was then determined by measuring the amount of incorporation of [³⁵S]-methionine and [³⁵S]-cysteine into cellular protein over 2 hours. The rate of protein synthesis in proliferating cells is shown for comparison. The results are shown as the mean ± standard deviation of nine independent plates of cells. (b) Quiescent cells were treated as in (a) and then either harvested immediately (0 hours after pulse) to assess the rate of total protein synthesis or washed and 'chased' with medium containing non-radioactive methionine and cysteine for 2 or 6 hours before harvesting to assess the rate of protein degradation. Each point represents the mean and range of three independent cultures. The rate of protein degradation is indicated by the slope of the line. The shallowness of the curve for the 24-hour-arrested cells is likely to be the result of the lower than expected value at 0 hours. The 0 hour result in (a) is likely to be more accurate, as it represents the mean of nine independent cultures, instead of three. If one uses the value of 80, the curve in (b) for the 24-hour-arrested cells would be steeper. The experiments in (a) and (b) were performed three times with similar results.