Changes in some chromatin and cytoplasmic enzymes of perinatal rat hepatocytes during culture

Hepatocytes prepared from rats at various perinatal stages were cultured in selective medium that does not allow fibroblastic cell growth. Cell population remained homogeneous during the culture. Hepatocytes undergo divisions for a period, which varies according to the stage of development of the rat. Light and electron microscope observations showed the presence of numerous cytoplasmic organelles; moreover, hydrocortisone-induced structures similar to bile canaliculi. Chromatin protein kinase decreased rapidly during culture except in samples prepared from 17-day fetuses in which it remained unchanged for 2 days and decreased to a lesser extent afterwards. Chromatin nonhistone proteins were incubated with (gamma-32P) ATP and the phosphorylation pattern analyzed on polyacrylamide gels. Many radioactive peaks were observed in chromatin proteins from 17-day fetuses; they were much lower in proteins than 19-day fetuses. The phosphorylation pattern was analyzed in hepatocytes after 2 days of culture. Many radioactive peaks were observed with proteins from hepatocytes taken from 17-day fetuses; no radioactivity was observed in proteins from 19-day fetuses. This is in contrast with the absence of radioactive peaks in chromatin proteins from adult rat hepatocytes. In cytoplasm, aldolase and pyruvate kinase specific activities varied according to the age of the rat. They strongly decreased during culture except in hepatocytes and 15- and 17-day fetuses, in which they remained stable for a least 5 days. The stability of chromatin and cytoplasmic enzymes in hepatocytes from 17-day fetuses could result from their ability to be regulated by hormones that are secreted at this stage of development.