FISH ERYTHROCYTES AS A TOOL TO STUDY TEMPERATURE-INDUCED RESPONSES INPLASMA-MEMBRANES

The dorsal aorta of carp (Cyprinus carpio L.) was cannulated, and the fish were kept in thermostated aquaria at 5-degrees-C for 24 h. The wa ter temperature was then gradually increased to 25-degrees-C at a rate of 0.5-degrees-C/h, and then decreased to 5-degrees-C at the same rat e. Blood was withdrawn at five-degree intervals to determine the fluid ity of erythrocyte plasma membranes upon ex vivo incorporation of the fluorescent dye, 3-[p-(6-phenyl-1,3,5-hexatrienyl)phenyl]propionic aci d. Steady-state anisotropy (R(ss)) of the plasma membranes increased a nd decreased with the increase and decrease in water temperature, resp ectively. The sterol-to-phospholipid ratio remained unchanged througho ut the thermal shifts. The fatty acid compositions of the total phosph olipids, of phosphatidylcholine and of phosphatidylethanolamine remain ed virtually unchanged, except for the level of arachidonic acid, whic h increased in erythrocytes from fish at the higher temperature (25-de grees-C). The molecular species compositions of phosphatidylcholines a nd phosphatidylethanolamines also remained unaffected throughout the t hermal shifts. The erythrocyte plasma membranes were more responsive t o temperature shifts in vivo than in vitro when percent efficacy was c ompared. Thus, factors other than lipid changes are conceivably involv ed in the adaptation of erythrocyte plasma membranes to short-term the rmal changes.