N

(f)

Figure 6 VGIC distributions in axons. At nodes of Ranvier, the identity of the sodium channel a-subunit changes during development in rat sciatic nerve. Panels (a), (c), and (e) present Nav1.2 immunoreactivity (red) data, whereas panels (b), (d), and (f) present pan-sodium channel immunoreactivity (red) data. Caspr immunoreactivity, a marker of the paranode, is shown in green. At all stages of development, nodes of Ranvier possess high densities of sodium channels (b, d, f). At early (a) but not late (e) stages, the predominant sodium channel isoform is Nav1.2. Scale bar: 10 mm. Reproduced from Rasband, M. N. and Trimmer, J. S. 2001. Developmental clustering of ion channels at and near the node of Ranvier. Dev. Biol. 236, 5-16, with permission from Elsevier.

Figure 6 VGIC distributions in axons. At nodes of Ranvier, the identity of the sodium channel a-subunit changes during development in rat sciatic nerve. Panels (a), (c), and (e) present Nav1.2 immunoreactivity (red) data, whereas panels (b), (d), and (f) present pan-sodium channel immunoreactivity (red) data. Caspr immunoreactivity, a marker of the paranode, is shown in green. At all stages of development, nodes of Ranvier possess high densities of sodium channels (b, d, f). At early (a) but not late (e) stages, the predominant sodium channel isoform is Nav1.2. Scale bar: 10 mm. Reproduced from Rasband, M. N. and Trimmer, J. S. 2001. Developmental clustering of ion channels at and near the node of Ranvier. Dev. Biol. 236, 5-16, with permission from Elsevier.

densities are especially high in the juxtaparanodal regions (Wang et al., 1993; Arroyo et al., 1999; for review, see Rasband and Trimmer, 2001).

In sum, recent studies are revealing the molecular organization of nodal, paranodal, and juxtaparano-dal regions of myelinated axons. It is clear that interactions between the axon and myelinating glia are required to form and maintain these regions and the concomitant distributions of ion channels. A better understanding of the underlying mechanisms will provide insights about how ion channel expression and distributions are regulated during development. Moreover, the information could potentially be useful for intervention and treatment of conditions associated with demyelination or axon regeneration.

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