Minimising aerobic respiratory demands could form the basis to sub-lethal copper tolerance by rainbow trout gill epithelial cells in vitro

Mechanisms of Cu tolerance were investigated in respiratory epithelial cell cultures, from rainbow trout gills, by studying O-2 consumption and protei n synthesis rates, intracellular Na concentration and TER. The lowest conce ntration found to reduce O-2 consumption was 25 muM Cu. This did not affect either protein synthesis rate or intracellular Na concentration and was in terpreted in terms of copper tolerance; i.e., how these two energetically d emanding processes are maintained despite a reduction in aerobic ATP supply . The relationship between protein synthesis rate and synthesis cost is exp onential and the cost of protein synthesis in gill cells was found to be mi nimal (i.e., this cell occupies a position on the asymptotic section of the protein synthesis rate/synthesis cost model) and unaffected by 25 muM Cu. Thus protein synthesis rates could be maintained since any reduction would represent an insignificant energy saving. Intracellular Na concentrations a nd O-2 consumption rates were linearly correlated suggesting reducing intra cellular maintenance costs would have a greater significance in terms of ov erall energetic conservation. Intracellular Na maintenance costs, calculate d from O-2 consumption rates and intracellular Na concentrations, were foun d to decline after exposure to 25 muM Cu. Since TER was unaffected this imp lied the reduced costs arose from membrane `channel arrest'. Thus the Na/K ATPase energy demands, associated with maintaining intracellular Na concent ration, could be reduced by decoupling metabolic demand and membrane functi on. Therefore this study may demonstrate how the flexibility of cellular en ergetics enables gill epithelial cells to tolerate sub-lethal Cu.