The effects of exogenous GM1 ganglioside on depolarization and ligand-induced Ca2+ signaling were investigated in PC12 cells. Cellular responses to K+ depolarization and bradykinin application in control and GM1-treated cells were examined with respect to: 1) changes in the intracellular Ca2+ concentration ([Ca2+]i) measured using fura-2 fluorescence in single cells, and 2) changes in Ca(2+)-dependent protein kinase activity as assayed by two-dimensional phosphopeptide analysis of the

more »

... fic phosphorylation of tyrosine hydroxylase. Pretreatment of cells with GM1 (10 or 100 microM) enhanced K+ depolarization-stimulated increases in [Ca2+]i and in 32PO4 incorporation into tyrosine hydroxylase phosphopeptide T2, a Ca2+/calmodulin-dependent protein kinase II substrate. In contrast, GM1 treatment had no effect on the transient increases in [Ca2+]i evoked by bradykinin or on bradykinin-induced increases in the site-specific phosphorylation of tyrosine hydroxylase. The depolarization-induced and GM1-enhanced increases in [Ca2+]i and T2 phosphorylation were prevented by removal of external Ca2+ or pretreatment with 1 microM nitrendipine, suggesting that these increases result from Ca2+ entry through dihydropyridine-sensitive Ca2+ channels. The ability of exogenous gangliosides to potentiate increases in [Ca2+]i may underlie their diverse neuritogenic and neurotrophic actions in the nervous system.