A comparison of protein synthetic patterns of MDCK cells grown in serum and hormonally defined serum‐free medium

The development of hormonally defined serum‐free media (HDM) for the culture of mammalian cells has allowed the study of specific cellular functions in a totally defined environment. Recently, several reports have indicated that there are differences in the basic cellular physiology of cells cultured in HDM when compared to cells cultured by the more traditional method of using serum‐supplemented culture media (SM). We report here that there are significant changes in the protein synthetic pattern in MDCK cells grown in HDM. There were no changes exhibited during the first passage in HDM, but following 10 passages in HDM there was an increased isotope ratio of (1) plasma membrane proteins with molecular weights of 12,000, 36,000 and 68,000 and (2) endoplasmic reticulum proteins with molecular weights of 12,000 and 37,000. Additionally, the incorporation of methionine and uridine were significantly increased in cells cultured in HDM for 10 passages. At present, we believe that these changes in the protein synthetic patterns are due at least partially to increased protein synthesis as indicated by monosome/polysome ratios. Therefore, though the use of HDM offers a completely defined system for studying cellular function, results obtained using HDM must be interpreted with caution when comparing them to previous studies that have used SM.