EFFECTS OF TEMPERATURE AND INTRACELLULAR PH ON THE SPHINGOMYELIN METABOLISM IN THE GILLS OF CRAB, CARCINUS-MAENAS

Temperature shift from 12 to 22 degrees C induced significant changes in the gill phospholipids of the crab Carcinus maenas 24 hr after temp erature change. High temperature adaptation affects the distribution o f L-3(H-3)serine in phosphatidylcholine (PC), phosphatidylethanolamine (PF) and sphingomyelin (SPH) but not in phosphatidylserine. The maxim um effect is observed during the first 24 hr after the in vivo adminis tration of the precursor, suggesting the presence of two pools of thes e 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 acetol ysis of these radiolabeled phospholipids showed that tile radioactivit y is mainly recovered in the diacylglycerol moities of PC and PE and i n the nitrogenous base parr. of the SPH. Injection of radiolabeled ser ine in 12 degrees C adapted crabs 8 hr before their abrupt transfer to 22 degrees C confirms the early increase of the label in SPH and PC p reviously observed. In this experiment, the relative specific activity of SPH-sphingosine exhibits an immediate and large increase. From the se observations, it appears probable that when external temperature ra pidly varies, changes in the rate of SPH pathway occurs, providing sig nal molecules necessary for the adaptation mechanisms. As temperature induces changes in intracellular pH, an in vitro measure of H-3-serine incorporation into SPH gives similar increases when intracellular pH is modified by adding 30 mM ammonium chloride in the incubation medium . (C) 1997 Elsevier Science Inc.