Small cooperative activity of old rat hepatocytes may depend on composition of the intercellular medium.

Ultradian oscillations of protein synthesis were used as a marker of hepatocyte synchronous cooperative activity producing a common rhythm in vitro; amplitude of the rhythm defines expression of the cell cooperation. Dense synchronous and sparse non-synchronous rat hepatocyte cultures on slides in a serum-free incubation medium 199 supplemented with 0.2 mg/ml albumin and 0.5 microg/ml insulin have been studied. The amplitude of the rhythm averaged approximately 2x in dense cultures of young (3 month old) rats than in old (2 year old) rats. But some cultures of young rats had the amplitude patterns similar to cultures of old rats, and vice versa. Addition to the medium of either 0.3 microM bovine brain gangliosides or 2 microM phenylephrine resulted in increase of the oscillation amplitude in dense cultures of old rats to the level inherent in young ones. Addition to the medium of 10% rat blood serum in non-synchronous sparse cultures from young rats resulted in detection of a protein synthetic rhythm. Although after serum from young rats, the rhythm expression was high, the rhythm after serum from old rats had been given was weak. Addition of gangliosides to old-rat serum resulted in synchronization of sparse cultures with amplitudes inherent of young-rat serum. The data tend to the conclusion that cell cooperation depends to a greater extent on the composition of the medium rather than on the age of the cell or animal.