XXXX induced by raised intracellular calcium.

@entity8862 @entity17 @entity1025 @entity39 @entity3281 @entity141 @entity15410 @entity16 @entity515 @entity1360 @entity8594 @entity3411 @entity3365 @entity35 @entity43334
Incubation of nerve with high concentrations of the divalent cation ionophore @entity3365 produces myelin vesiculation (Schlaepfer 1977). This observation has now been extended using segments of @entity35 ventral or dorsal root incubated with high (19 microM, 10 micrograms/ml) or low (1-1.5 microM) concentrations of @entity3365 , or another divalent ionophore, @entity1360 . Low concentrations of @entity3365 induced no vesiculation within a 2-h period. However, subsequent incubation of these roots in fresh, ionophore-free medium for 20 h, resulted in a @entity17 at the Schmidt-Lanterman incisures and paranodes of many fibres. At this time (22 h) the Schwann cells associated with some demyelinating internodes appeared vital upon ultrastructural examination: the cells also excluded the nuclear dye nigrosin. High concentrations of @entity3365 induced a similar @entity17 in affected fibres within only 15-20 min. While the Schwann cells continued to exclude @entity43334 for a further 4 h, their ultrastructural appearance indicated that they were probably in the early stages of @entity39 . Incubation of moribund root with the ionophore produced no myelin vesiculation. At all ionophore concentrations, the myelin vesiculation was dependent upon the presence of extracellular @entity141 , and could be modulated in severity by varying this concentration. Other divalent cations ( @entity8594 , @entity515 , @entity1025 , @entity3281 , @entity3411 , @entity15410 ) could not substitute for @entity141 . The vesiculation induced by @entity3365 could be entirely prevented by the addition of @entity8862 (greater than or equal to 1 microM), @entity3411 (greater than or equal to 1-10 microM), @entity515 (greater than or equal to 100 microM) or @entity3281 (greater than or equal to 100 microM) to the bathing medium. @entity3365 applied to only part of an isolated internode resulted in a localization of the myelin disruption to that region. @entity1360 (greater than or equal to 1 microM), an ionophore with a greater selectivity for @entity141 than @entity3365 , also induced a prompt @entity141 -dependent myelin vesiculation. We conclude that @entity17 can be initiated in vital Schwann cells by a raised intracellular @entity141 concentration. Such @entity17 does not necessarily lead to Schwann cell death. The possible relevance of the findings to vesicular demyelinating @entity16 is discussed, and a hypothesis regarding the mechanism of @entity17 is advanced.
