Histamine Acting on H2Receptors Stimulates Phospholipid Methylation in Synaptic Membranes of Rat Brain

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Abstract
Histamine stimulated [3H]methyl group incorporation into phospholipids in crude synaptic membranes of rat whole brain (without cerebellum) in modified Krebs-Ringer solution containing the methyl donor S-adenosyl-[methyl-3H]methionine. The transient increase of [3H]-methyl incorporation into lipids peaked within 45 s after addition of histamine (5 or 10 .mu.M) and decreased the basal level in 60 s. Histamine-stimulated [3H]methyl incorporation was increased linearly in a protein concentration-dependent manner. The stimulation was temperature and histamine concentration dependent. TLC analysis of a chloroform/methanol extract indicated that radioactive phospholipids (phosphatidylcholine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidyl-N-monomethylethanolamine) accounted for 60-65% of the total radioactivity recovered. The synaptosomal fraction had the highest specific activity of all the subfractions of crude synaptic membranes (P2). Histamine-induced [3H]methyl incorporation was inhibited by addition of cimetidine (0.01-10 .mu.M) or famotidine (0.01-1.0 .mu.M) in a concentration-dependent manner but not by mepyramine (0.1-10 .mu.M) or diphenhydramine (0.1-10 .mu.M). The stimulation of [3H]methyl incorporation was also observed by addition of impromidine (0.01-10 .mu.M) or dimaprit (1.0.mu.M-1.0 mM) in a concentration-dependent manner but not by 2-pyridylethylamine (1.0 .mu.M-1.0 mM). These results indicate that phospholipid methylation is induced by histamine acting on H2 receptors in rat brain synaptosomes.

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