Related Experiment Videos
Histamine acting on H2 receptors stimulates phospholipid methylation in synaptic membranes of rat brain
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 microM) 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 microM) or famotidine (0.01-1.0 microM) in a concentration-dependent manner but not by mepyramine (0.1-10 microM) or diphenhydramine (0.1-10 microM). The stimulation of [3H]methyl incorporation was also observed by addition of impromidine (0.01-10 microM) or dimaprit (1.0 microM-1.0 mM) in a concentration-dependent manner but not by 2-pyridylethylamine (1.0 microM-1.0 mM). These results indicate that phospholipid methylation is induced by histamine acting on H2 receptors in rat brain synaptosomes.
Insights
Histamine stimulates phospholipid methylation in rat brain synaptosomes, primarily via H2 receptors. This process involves phosphatidylcholine and related lipids, with activity dependent on histamine concentration and temperature.
Area of Science:
- Neuroscience
- Biochemistry
- Pharmacology
Background:
- Histamine is a key neurotransmitter in the central nervous system.
- Phospholipid methylation plays a role in membrane function and signal transduction.
- The specific receptors and mechanisms mediating histamine's effects on phospholipid metabolism in the brain remain areas of investigation.
Purpose of the Study:
- To investigate the effect of histamine on phospholipid methylation in rat brain synaptosomes.
- To identify the specific phospholipids involved in histamine-stimulated methylation.
- To determine the receptor subtypes mediating this response.
Main Methods:
- Crude synaptic membranes from rat brain were incubated with S-adenosyl-[methyl-3H]methionine.
- Histamine and various receptor antagonists/agonists were added to assess effects on [3H]methyl incorporation.
- Thin-layer chromatography (TLC) was used to analyze radioactive phospholipid composition.
- Specific activity was measured in different subfractions of synaptic membranes.
Main Results:
- Histamine significantly increased [3H]methyl incorporation into phospholipids in a time-, concentration-, and temperature-dependent manner.
- Radioactive phospholipids, including phosphatidylcholine and its methylated derivatives, constituted the majority of the incorporated radioactivity.
- The synaptosomal fraction exhibited the highest specific activity.
- Cimetidine and famotidine (H2 receptor antagonists) inhibited histamine-induced methylation, while mepyramine and diphenhydramine (H1 antagonists) did not.
- Impromidine and dimaprit (H2 receptor agonists) mimicked histamine's effect, while 2-pyridylethylamine did not.
Conclusions:
- Histamine induces phospholipid methylation in rat brain synaptosomes.
- This effect is mediated by the activation of H2 receptors.
- Phosphatidylcholine and its methylated forms are key substrates in this histamine-stimulated process.