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To study ganglioside distribution within subcellular components and test the hypothesis that they are localized at the nerve ending, microsomes and synaptic plasma membranes were isolated from young adult rat brains and compared with respect to ganglioside composition. These were shown to be heterogeneous preparations by fractionation on a discontinuous sucrose gradient into subfractions which had differing ganglioside concentrations. The highest ganglioside concentrations occurred in membranes banding at the 0.8M/1.0M and 1.0M/1.3M interfaces for both microsomes and synaptic plasma membranes. These subfractions had closely similar ganglioside concentrations and pattern distributions. In addition, the kinetics of ganglioside labeling following administration of [3H]-glucosamine were similar for the two preparations. The fact that microsomal subfractions representing heterogeneous mixtures of brain cell membranes showed close similarity to synaptosomal plasma membranes argues against localization of gangliosides at the nerve ending. These results, together with other lines of evidence, support the concept that gangliosides are distributed over large portions of the neuron (and perhaps other brain cells). Data concerning the labeling of gangliosides in different microsomal subfractions indicated a movement of label over time from the more dense to the less dense membranes, as was also noted for the glycoproteins in the same subfractions. Specific radioactivity of the gangliosides increased relative to that of the glycoproteins with time.

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The ganglioside composition of calf aortic smooth muscle cells, cultured in the presence and absence of ascorbate, was analyzed. Previous work has shown that ascorbate supplementation leads to the formation of an extracellular matrix consisting primarily of collagen and that this matrix influences the biosynthetic capabilities of the cell. Cell cultures were supplemented with ascorbate for 3 wk and labeled with [14C]glucosamine for 3 d before harvesting. Ascorbate supplementation resulted in increased ganglioside sialic acid levels and a change in chromatographic profile involving both absolute and relative increases in GD1a. The latter, along with polysialo species, showed increased incorporation of [14C]glucosamine. These findings are interpreted in relation to the proposed role of gangliosides as mediators in the interaction of various cells with extracellular matrix.