Comparison of basal and noradrenaline stimulated methylation of chloroform-extractable products in synaptosomal preparations from the rat brain

The influence of picrotoxin on the methylation of phospholipids of the olfactory cortex of the brain of rats

It was demonstrated that a decrease in the intensity of methylation of phosphatidylethanolamine in sections of rat olfactory cortex is observed 15 min following the introduction of picrotoxin (10(-5) M) into the incubation medium. The decrease in the intensity of methylation of phospholipids may be closely linked to the opening of ion channels, since it is known that maximal depolarization of the membranes is observed during this period of the effect of the preparation.

Increased methylation of chloroform extractable products in brain membrane preparations after propranolol injection to the rat

1. One and four hours after acute or chronic (8 days) intraperitoneal injection of propranolol to rat at doses up to 25 mg/kg, a beta-adrenergic receptor blockage occurred in brain homogenates, as monitored by [3H]dihydroalprenolol binding. 2. A dose-dependent increased methylation of chloroform extractable products was observed (acute treatment: 18% increase, chronic treatment: 136% increase for the dose of 25 mg/kg). 3. The implication of beta-adrenergic receptors in this effect was studied and this revealed that: (a) acute intraperitoneal injection of the less active propranolol stereoisomer (+) did not produce any effect; (b) the chronic intraperitoneal injection of salbutamol, a beta-adrenergic receptor agonist, induced a decreased methylation of chloroform extractable products (62% decrease for the dose of 2.5 mg/kg). 4. It is concluded that injection of beta-adrenergic antagonist to the rat increases basal methyltransferase activity in the brain. This induces a decreased sensitivity of the enzyme activity to noradrenaline.

Alteration of membrane phospholipid methylation by adenosine analogs does not affect T lymphocyte activation

Membrane phospholipid methylation has been described during activation of various immune cells. Moreover recent data indicated modulation of immune cells functions by adenosine. As S-Adenosyl-methionine and S-Adenosyl-homocysteine are adenosine analogs and modulators of transmethylation reactions, the effects of SAH and SAM were investigated on membrane phospholipid methylation and lymphocyte activation. SAM (10(-5) M) was shown to induce the membrane phospholipid methylation as assessed by the 3H-methyl-incorporation in membrane extract. This effect was inhibited by SAH. In contrast SAM and SAH did not affect the phytohemagglutinin-induced proliferative response of peripheral blood mononuclear cells. SAH neither modified the early internalization of membrane CD3 antigens nor did it prevent the late expression of HLA-DR antigens on lymphocytes activated by phytohemagglutinin. These results indicate that in vitro alteration of phospholipid methylation does not affect subsequent steps of human T lymphocyte activation and proliferation.

Effect of toluene on rat synaptosomal phospholipid methylation and membrane fluidity

This study investigated the effects of toluene (1 g/kg, 1 hr, i.p.) on rat synaptosomal phospholipid methylation (PLM), phospholipid composition, and membrane fluidity. Toluene significantly decreased basal PLM (35%) in studies using [3H]methionine [( 3H]Met) as the methyl donor; this was reflected by similar decreases in phosphatidylmonomethylethanolamine (PME) (30%). No effects were observed in either PLM reactions that used [3H]adenosylmethionine [( 3H]AdoMet) as methyl donor, or AdoMet synthetase, suggesting that toluene preferentially affects PLM reactions that derive methyl groups from [3H]Met. Also, toluene decreased synaptosomal phosphatidylethanolamine (PE) (24%), the initial substrate for PLM, and the addition of PE back to PE-depleted synaptosomes restored methyltransferase activity. Agonist-stimulated PLM using norepinephrine (NE) demonstrated that agonist-receptor coupling returned PLM to control values in synaptosomes from toluene-treated rats. NE-stimulated PLM was also blocked by propranolol (PRO), suggesting a role for toluene in receptor-mediated events. Membrane fluidity studies demonstrated that in vivo administration of toluene increased the outer synaptosomal membrane fluidity, whereas in vitro administration of toluene had no effect. Our observations support a positive relationship between increased PLM activity and increased outer, not core, membrane fluidity. These data demonstrate that specific toluene-phospholipid interactions occur in synaptosomes, resulting in altered membrane composition, function and fluidity.