Relation between membrane fluidity and signal transduction in the human megakaryoblastic cell line MEG-01

Abstract

The fluidity of the plasma membrane is thought to affect the responsiveness of blood platelets. We measured membrane fluidity in a single cell by Fluorescence Recovery after Photobleaching (FRAP) of the lipophilic probe DiIC14. Since platelets are too small for this technique, we used the human megakaryoblastic cell-line MEG-01, which shares many properties with platelets. MEG-01 cells were cultured for 44 h with simvastatin or mevalonate to change the cholesterol content, enabling analysis of signal processing at cholesterol/phospholipid ratios (C/P) between 0.20 and 0.31. The diffusion of DiIC14 correlated inversely with the C/P ratio with lateral diffusion coefficients (D) of 3.28 x 10(-9) cm2/s at a low C/P decreasing to 2.55 x 10(-9) cm2/s at a high C/P ratio. The mobile fraction was 65% and constant at the different C/P ratios. The relation between lipid diffusion and signal processing was measured following stimulation with 10 U/ml thrombin at 22 degrees C. There were only little differences in phosphatidylinositol metabolism, Ca2+ influx or mobilization and prostaglandin I2-induced formation of cyclic AMP. At 37 degrees C, cells with a high C/P ratio showed increased phosphatidylinositol metabolism, but these differences had no major effect on the Ca2+ responses. These data demonstrate that in megakaryoblasts the lateral diffusion of lipids is inversely correlated with the C/P ratio, but within the range of 0.20-0.31 the influence on signal processing is minor.

Blood Platelet Reactivity and its Pharmacological Modulation in (People with) Diabetes Mellitus

“…Associated with such changes in membrane lipid composition, blood platelets have been demonstrated to become more sensitive to aggregation induced by adrenalin or ADP [58][59][60][61][62]. On the other hand, there are reports showing that the interaction of protein and peptide ligands with platelet membrane receptors leads to the changes in the organisation of membrane components, and such displacements in membrane protein projection could be mediated by the alterations of membrane lipid fluidity [43,54,59,[63][64][65][66].…”

“…The relation between platelet membrane fluidity and signal transduction in human platelets remains indefinable, however, the fluidity of platelet plasma membranes is thought to effect the responsiveness of blood platelets [43,59,[67][68][69][70][71][72]. The impaired macromolecular interactions in membrane, associated with the reduced diffusion of various membrane components, are believed to modulate cell receptor-mediated signal transduction [47].…”

“…Membrane lipid bilayer fluidity plays an important role in cellular functions, and blood platelets are not unique in that respect [43]. Overwhelming evidence has accumulated confirming that membrane fluidity is involved in the control of an increasing number of physiological processes and that derangements of normal fluidity may occur in some pathological states [44][45][46].…”

Plausible explanations for effects of long chain polyunsaturated fatty acids (LCPUFA) on neonates

“…Increased phosphatidylcholine unsaturation, which results in more fluidity, increases the activity of protein kinase C29; in contrast, higher cholesterol:phospholipid ratios in the plasma membrane (a more rigid membrane) increase cyclic AMP concentrations in megakaryoblasts 30…”

Platelet membrane lipid fluidity and intraplatelet calcium mobilization in type 2 diabetes mellitus

“…In line with such a suggestion we revealed a significant correlation between the reduced platelet membrane fluidity and more intense calcium mobilization in diabetic platelets. The relationship between the dynamic parameters of cell membrane lipid bilayer, calcium mobilization and cell activation was validated earlier with the use of various modulators of membrane lipid fluidity (25)(26)(27)(28), which have been reported to inhibit spontaneous Ca2+ release in numerous cell types, probably due to their direct interaction with a Ca2+ channel rather than with other permeability pathways (29)(30)(31). In our earlier studies we also reported that the preventive effects of procaine on platelet release reaction and calcium mobilization might relate to the changes in the organization of membrane components embedded into a lipid bilayer, which are crucial in triggering of platelet release reaction.…”