Cholera toxin (CT) has been reported to bind specifically to GM1 ganglioside on cell surface plasma membranes and activates adenylate cyclase. We examined whether or not GM1 ganglioside (ga-lactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosyl-glucosylceramide) accumulates in plasma membranes of cultured skin fibroblasts from GM1 gangliosidosis patients by measuring cyclic AMP (adenosine 3’,5'-cyclic monophosphate; cAMP) production elicited by CT. Optimal conditions for the assay were determined to be 1 μg/ml of CT and 1 h incubation at 37°C. The responses of intracellular cAMP level to a direct activator of adenylate cyclase, forskolin, and to phorbol 12-myristate 13-acetate (PMA) were not different between patients and controls. Insertion of exogenous GM1 ganglioside into the cell membrane caused a linear increase in the cAMP production triggered by CT in control cells. Under the optimal conditions, intracellular cAMP production in response to CT was estimated as 544.3+16.3 pmol/h per mg protein in the patients’ cells and 284.8 + 46.8 pmol/h per mg protein in the control ones. These data are the first indication of the accumulation of GM1 ganglioside in cell surface membranes of patients with GM1 gangliosidosis.
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