PHOSPHATIDYLINOSITOL AND OTHER LIPIDS IN A MAMMALIAN SYMPATHETIC GANGLION: EFFECTS OF NEURONAL ACTIVITY ON INCORPORATION OF LABELLED INOSITOL,PHOSPHATE, GLYCEROL AND ACETATE1

Abstract— Superior cervical ganglia from adult rats were incubated for 1–6 h in a physiological salt solution containing ³²P_i [2-³H]inositol, [U-¹⁴C]glycerol, or [U-¹⁴C]acetate. Control ganglia were at rest throughout incubation, while the preganglionic nerves of the experimental ganglia were stimulated at 5/s, starting after 1 h of incubation. Responses were monitored by recording the action potentials in a postganglionic nerve. Radioactivity of phospholipids was counted after separation of the lipids by paper chromatography. Specific activity of free inositol and the gamma-phosphate of ATP were measured, the latter by using the hexokinase reaction with [¹⁴C]glucose, isolating the product, and counting its content of ³²P and ¹⁴C. At rest, labelling of phosphatidylinositol (PI), phosphatidylcholine and phosphatidylethanolamine proceeded at constant rates for at least 8 h with all precursors which entered them, except that labelling with glycerol slowed after 2–4 h. During stimulation the rate of incorporation of ³²P into PI approximately doubled, as previously reported. The increased rate remained constant for 3 h and then reverted to approximately the resting rate, although the electrical response continued unabated for 16 h. This decrease in rate of ³²P-labelling of PI in the ganglion could not be accounted for by transport into the postganglionic nerves. In stimulated preparations, after 4 h of incubation the labelling of PI was increased above the resting level by 53 ± 5% (mean ±s.e.m. ) with [³H]inositol, 97 ± 6% with ³²P_i, 24 ± 6% with [¹⁴C]glycerol and ?3 ± 10% with [¹⁴C]acetate. The increase with glycerol was thus statistically significant, in contrast with the findings of others on brain, where an increase of this size has neither been demonstrated nor excluded. There were no accompanying effects of stimulation on the specific activities of the gamma-P of ATP or of the free inositol within the ganglion that were sufficient to explain the difference between the labelling of PI with P and that with inositol.