Modulatory effects of different temperatures and Ca2+ concentrations on gangliosides and phospholipids in monolayers at air/water interfaces and their possible functional role

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Abstract
Summary 1. Gangliosides are neuraminic acid-containing glycolipids preferently localized in nervous membranes and showing physicochemical peculiarities, e.g., drastically changing amphiphilic properties by Ca2+ binding. On account of this they are favorite compounds to act as modulators of membraneous organization and functions during synaptic transmission. Lipid monolayers are suitable experimental systems for the study of the surface behavior of amphipatic molecules and therefore are useful to interpret membraneous organization. 2. The surface pressure/area isotherms of monolayers of different individual gangliosides (GM1, GD1a, GD1b, GT1b) of an artificial reconstituted and a natural ganglioside mixture from bovine brain and of ganglioside mixtures from different brain parts of summer- and winter-adapted dsungarian hamsters were compared at three temperatures (11, 20, and 37°C) with egg phosphatidylcholine (PC) and phosphatidylserine (PS) monolayers. The monolayers were formed in a Teflon trough on a triethanolamine/HCl-buffered (pH 7.4) subphase, in some cases containing different amounts of CaCl2. 3. The surface pressure/area isotherms of ganglioside monolayers, in contrast to phospholipids, generally showed slowly rising slopes, with transitions from the liquidexpanded to the liquid-condensed state at a surface pressure of 20–30 mN/m. Ganglioside monolayers, in particular from GD1a or GT1b versus GD1b or from mixtures from summer- versus winter-adapted hamster brain, were differently affected by temperature and/or by Ca2+. PS monolayers were slightly condensed only by Ca2+. PC monolayers, however, were influenced neither by temperature nor by Ca2+. In mixed monolayers of the unpolar natural lipid cholesterol (Ch) and the disialoganglioside GD1a, intermolecular interactions were indicated. 4. Ganglioside monolayers, in contrast to phospholipids, were shown to be easily modulated by temperature and/or Ca2+ ions, thus enabling gangliosides to act as possible membrane modulators, e.g., during synaptic transmission. In particular, the differences concerning the influences of temperature and/or Ca2+ on the surface behavior of ganglioside mixtures from the brain of summer- compared with winteradapted hamsters are correlated with other physiologically relevant data.