Age-related features of protein synthesis rhythm. Effects of extracellular medium

Abstract

Circahoralian, or ultradian, intracellular rhythms, including protein synthesis rhythm, were described in various cells both in situ and in vitro (for reviews see Brodsky, 1975; Ultradian Rhythms …, 1992). They have been studied for a long time in the cultures of hepatocytes as well. Visualization of any rhythm in a cell culture is only possible when oscillations are synchronized due to intercellular cooperation. The rhythm expression depends on the degree of synchrony, i.e., on cooperative activity of cell in the formation of an aggregate rhythm of a cell population. The amplitude of rhythm, or range of oscillations, is a visible reflection of this cooperation. In the case when each individual cell has a rhythm, but oscillations in different cells are antiphasic, the aggregate kinetics of a population will not be oscillatory. When the phases of oscillations correspond to each other, a rhythm is visualized and, the closer the phases of oscillations of individual cells, the higher the amplitude of the aggregate rhythm.We have already shown that the amplitude of oscillations of protein synthesis intensity in the cultures of hepatocytes from old rats is lower than that from young animals (Brodsky et al. , 2001), which characterized a low cooperative activity of the cells of old animals. However, these data were preliminary: we assayed the kinetics of protein synthesis only in two old rats. In order to confirm the first observations, it was necessary to carry out experiments of a larger material and, in case of a positive result, clarify possible causes of agerelated changes and establish to what extent they are reversible.When studying intercellular cooperation, we investigated dense, fast self-synchronizing in a fresh medium, hepatocytes and sparse asynchronous cultures (Brodsky et al. , 1994(Brodsky et al. , , 1996a. We used the synchronizers we found earlier: gangliosides (Brodsky et al. , 1996a(Brodsky et al. , , 1997Zvezdina et al. , 2000). Gangliosides are cell membrane glycolipids; they are constantly secreted in extracellular medium and incorporated in other cells and affect many intracellular processes (for reviews see Hakomori, 1981Hakomori, , 2000Tettamanti and Riboni, 1994;Yates and Rampersaud, 1998). In our experiments, asynchronous sparse cultures of hepatocytes were synchronized soon after addition of a standard mix of bovine brain gangliosides (BBG: 20% GM1, 40% GD1a, 16% GD1b, and ca. 4% of others) or individual fractions (GM1 or GD1a). The synchronizing effect of gangliosides can be reproduced by a medium conditioned by dense cultures (Brodsky et al. , 1995(Brodsky et al. , , 2000b.In order to simulate the influence of gangliosides on intracellular processes, we studied their well known effect on the concentration of calcium ions in the cytoAbstract -Cell interactions have been studied in cultures pf hepatocytes from young and old rats. The rhythm of protein synthesis is an index of cell interaction and synchronization in culture, while the amplitude of oscillations characterized cell cooperation i...

Melatonin Modifies the Rhythm of Protein Synthesis

“…The yeast respiration circahoralian rhythm phase is shifted under the effect of acetaldehyde [11]. Signal factors initiate the chain of processes, detected in our experiments as exemplifi ed by protein synthesis rhythm organization in hepatocyte culture [3,5,8].…”

“…Previously we have demonstrated a shift of protein synthesis phase in hepatocyte cultures treated with phorbol ether (protein kinase stimulant) [8]. Shift of circahoralian rhythm phases for activities of some enzymes were observed in experiments on transformed cells after addition of insulin (stimulating protein phosphorylation) [10] or retinoic acid [9] to the medium.…”

“…The study was carried out on primary cultures of rat hepatocytes [1,2,7,8]. Solid cultures with cells lying close to each other were used.…”

“…Isolated rat hepatocytes were cultured on collagen-coated slides in medium 199 with 0.2 mg/ml albumin and 0.5 μg/ml insulin with the gaseous phase consisting of 95% air and 5% CO 2 [7,8]. Solid cultures with densely lying hepatocytes were obtained by inoculating about 10 6 cell/ml into Petri dishes.…”

“…These cultures autosynchronize 10-15 min after replacement of the medium. Cultures without melatonin (control) were compared to cultures treated with melatonin alone or melatonin against the background of luzindole (melatonin receptor blocker).Isolated rat hepatocytes were cultured on collagen-coated slides in medium 199 with 0.2 mg/ml albumin and 0.5 μg/ml insulin with the gaseous phase consisting of 95% air and 5% CO 2 [7,8]. Solid cultures with densely lying hepatocytes were obtained by inoculating about 10 6 cell/ml into Petri dishes.…”