Temperature shift from 12 to 22°C induced significant changes in the gill phospholipids of the crab Carcinus maenas 24 hr after temperature change. High temperature adaptation affects the distribution of L- 3(3H)serine in phosphatidylcholine (PC), phosphatidylethanolamine (PE) and sphingomyelin (SPH) but not in phosphatidylserine. The maximum effect is observed during the first 24 hr after the in vivo administration of the precursor, suggesting the presence of two pools of these phospholipids in the gill cells. One pool seems to be very sensitive to the temperature, whereas the second presents the similar kinetics at the different temperatures tested. Enzymatic degradation and acetolysis of these radiolabeled phospholipids showed that the radioactivity is mainly recovered in the diacylglycerol moities of PC and PE and in the nitrogenous base part of the SPH. Injection of radiolabeled serine in 12°C adapted crabs 8 hr before abrupt transfer to 22°C confirms the early increase of the label in SPH and PC previously observed. In this experiment, the relative specific activity of SPH-sphingosine exhibits an immediate and large increase. From these observations, it appears probable that when external temperature rapidly varies, changes in the rate of SPH pathway occurs, providing signal molecules necessary for the adaptation mechanisms. As temperature induces changes in intracellular pH, an in vitro measure of3H-serine incorporation into SPIt gives similar increases when intracellular pH is modified by adding 30 mM ammonium chloride in the incubation medium.
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