Trophic effect of cholera toxin B subunit in cultured cerebellar granule neurons: modulation of intracellular calcium by GM1 ganglioside.
Survival of cerebellar granule cells (CGC) in culture was significantly improved in the presence of cholera toxin B subunit (Ctx B), a ligand which binds to GM1 with specificity and high affinity. This trophic effect was linked to elevation of intracellular calcium ([Ca2+]i), and was additive to that of high K+. Survival was optimized when Ctx B was present for several days during the early culture period. 45Ca2+ and cell survival studies indicated the mechanism to involve enhanced influx of Ca2+ through L-type voltage-sensitive channels, since the trophic effect was blocked by antagonists specific for that channel type. Inhibitors of N-methyl-D-aspartate receptor/channels were without effect. During the early stage of culture Ctx B, together with 25 mM K+, caused [Ca2+]i to rise to 0.2-0.7 microM in a higher proportion of cells than 25 mM K+ alone. A significant change in the nature of GM1 modulation of Ca2+ flux occurred after 7 days in culture, at which time Ctx B ceased to elevate and instead reduced [Ca2+]i below the level attained with 25 mM K+. GM1 thus appears to serve as intrinsic inhibitor of one or more L-type Ca2+ channels during the first 7 days in vitro, and then as intrinsic activator of (possibly other) L-type channels after that period. This is the first demonstration of a modulatory role for GM1 ganglioside affecting Ca2+ homeostasis in cultured neurons of the CNS.
Wu
G
G
Department of Neurosciences, New Jersey Medical School of UMDNJ, Newark 07103, USA.
Lu
Z H
ZH
Nakamura
K
K
Spray
D C
DC
Ledeen
R W
RW
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002132:Calcium Radioisotopes; D002454:Cell Differentiation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002772:Cholera Toxin / Q000494:pharmacology*; D005456:Fluorescent Dyes; D016257:Fura-2; D005677:G(M1) Ganglioside / Q000502:physiology*; D007091:Image Processing, Computer-Assisted; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors; D013050:Spectrometry, Fluorescence
D002121:Calcium Channel Blockers; D002132:Calcium Radioisotopes; D005456:Fluorescent Dyes; D016194:Receptors, N-Methyl-D-Aspartate; D005677:G(M1) Ganglioside; D002772:Cholera Toxin; D002118:Calcium; D016257:Fura-2