Influence of lysophosphatidylcholine, phosphatidylcholine, and hen egg yolk on contractile effects of acetylcholine on smooth muscles of rat stomach

Abstract

Experiments on smooth muscles of rat stomach showed that lysophosphatidylcholine in concentrations of 10(-8) and 10(-7) g/ml does not modulate the tonotropic effect of acetylcholine (10(-6) g/ml), in a concentration of 10(-6) g/ml potentiated this effect (similarly to phosphatidylcholine, 10(-6) g/ml), and reduced it in concentrations of 10(-5)-10(-4) g/ml (similarly to hen egg yolk in dilutions of 1:500, 1:100, and 1:500). These data indicate that lysophosphatidylcholine modifies signal transduction from the receptor to G protein.

Effect of Lysophosphatidylcholine on α-Adrenoreactivity of Rat Aorta Smooth Muscles

“…We did not investigate the mechanisms underlying these effects of LPC, but we hypothesized that LPC can not only reduce, but also increase the effi ciency of activation of G-protein coupled receptors. This assumption is indirectly confi rmed by experiments [3], where LPC improves the effi ciency of activation of muscarinic cholinergic receptors in smooth muscles of the stomach in a concentration of 2×10 6 M, but reduces it in higher concentrations (2×10 5 and 2×10 4 M). From this standpoint it is clear that LPC can be considered as a natural factor modulating the effect of hormones on cell functioning and the direction of this modulating effect depends on LPC concentration in the medium.…”

“…These fi ndings suggest that myocytes of rat aorta are highly resistant to LPC. On the other hand, LPC was shown to reversibly reduce the effectiveness of β-AR activation in cardiomyocytes of rat and frog [4] and muscarinic receptors in frog and rabbit myocardium [5,6], myocytes of rat stomach [3] and blood vessels [12,13], including the aorta [14]. This suggests that LPC can reduce the effectiveness of transmembrane signal transduction from the receptors into the cell depends not only on the type of cells, but also on the type of G-protein coupled receptors.…”

“…Address for corespondence: tsirkin@list.ru. V. I. TsirkinIt had been previously shown that lysophosphatidylcholine (LPC) synthesized in the body decreases the effi ciency of activation of muscarinic cholinergic receptors in the myocardium [5,6] and smooth muscles of the stomach [3] and blood vessels [12][13][14]; therefore, LPC can be considered as a component of endogenous blocker of muscarinic cholinergic receptors, postulated to explain the antimuscarinic activity of blood serum [3,7,8]. It was shown that LPC attenuates the positive inotropic effect of epinephrine on frog and rat myocardium (i.e.…”