Effects of Temperature, Calcium and Activity on Phospholtpid Metabolism in a Sympathetic Ganglion
Larrabee, M.G.; Klingman, J.D.; Leicht, W.S.
Journal of Neurochemistry 10(8): 549-570
ISSN/ISBN: 0022-3042 DOI: 10.1111/j.1471-4159.1963.tb05053.x
Superior cervical ganglia excised from rats were incubated (usually at 37[degree]) in a physiological solution containing [p32]phosphate and [Cl4]glucose. Lipids were subsequently extracted, chromatogrammed on paper which had been impregnated with silicic acid, and scanned with a Geiger counter. By appropriate calibration, the labelling was expressed in terms of moles of phosphorus or carbon transferred from the bathing fluid per unit weight of tissue. Specific activities were determined on phospholipids separated by a silicic acid column. Phosphatidyl inositol, phosphatidyl choline, phosphatidyl ethanolamine, and phosphatidic acid became labelled with p32. At least the first three compounds were also labelled with C14. Phosphorus and carbon labelling both increased nearly linearly for more than 6 hr. Percentage labelling was small (about 0[center dot]1-1 per cent/hr). Neither label declined significantly if incubation was continued for several hours after removal of the isotopes from the bathing solution. Repetitive stimulation of the preganglionic nerve (1-10/sec) increased the incorporation of P32 into phosphatidyl inositol, but not into phosphatidyl choline, phosphatidyl ethanolamine or phosphatidic acid. The stimulation caused no significant changes in total phosphorus in any of these materials, with the possible exception of phosphatidic acid, which was not investigated. C14- labelling was increased significantly by stimulation in phosphatidyl inositol, probably in phosphatidyl choline, but not in phosphatidyl ethanolamine. In resting ganglia reduction of temperature altered the C14- and p32-iabelling according to a Q10 of 2[center dot]6-3[center dot]7 in most instances. Exceptions were a larger effect on p32. labelling of the choline and ethanolamine phosphatides (Q10 = 7), and a smaller effect on C14 incorporation into phosphatidyl inositol (Q40 = 1-7). During activity the absolute increment per impulse discharged in the amount of 32p in the inositide appeared to be independent of temperature. Reduction of calcium in the fluid bathing a resting ganglion had strikingly differential effects on labelling in phosphatidyl inositol, C14 increased, but p32 was not affected; in phosphatidyl choline and phosphatidyl ethanolamine, C14 was unchanged, but P32 decreased; in phosphatidic acid, P32 decreased. These results could be explained by assuming that withdrawal of calcium reduced the specific activity of phosphate precursors and stimulated the synthesis of phosphatidyl inositol. The latter effect may have resulted from neuronal activity caused by the removal of calcium. Some observations were also made on C-labelling of a chromatographic component containing simple lipids, presumably including cholesterol.