The effects of cell ageing on protein synthesis in rainbow trout (Oncorhynchus mykiss) red blood cells.

The effects of cell age on protein synthesis were examined in the nucleated red blood cells of rainbow trout (Oncorhynchus mykiss). Total DNA content was unaffected by cell age, whereas total RNA content in young red blood cells was roughly ten times as high as that in old red blood cells. The mRNA levels for haemoglobin, carbonic anhydrase and the chloride/bicarbonate (Cl(-)/HCO(3)(-)) exchanger were also approximately tenfold higher in young red blood cells. Although young red blood cells synthesized roughly five times more protein under steady-state conditions, total protein concentration was not affected by cell age. Despite large reductions in mRNA levels with red blood cell ageing, the concentrations and/or activities of the respiratory proteins were largely preserved. In contrast, the ability to mount a heat shock response was greatly reduced in older red blood cells. Young red blood cells produced 13 times more heat shock protein 70 mRNA following heat shock and four times more 70 kDa protein after recovery. They also transcribed much more heat shock cognate 71 and heat shock factor mRNA than did older red blood cells under steady-state conditions.