Distribution and lateral mobility of voltage-dependent sodium channels in neurons [published erratum appears in J Cell Biol 1989 May;108(5):preceding 2001]

Abstract

Abstract. Voltage-dependent sodium channels are distributed nonuniformly over the surface of nerve cells and are localized to morphologically distinct regions. Fluorescent neurotoxin probes specific for the voltagedependent sodium channel stain the axon hillock 5-10 times more intensely than the cell body and show punctate fluorescence confined to the axon hillock which can be compared with the more diffuse and uniform labeling in the cell body. Using fluorescence photobleaching recovery (FPR) we measured the lateral mobility of voltage-dependent sodium channels over specific regions of the neuron. Nearly all sodium channels labeled with specific neurotoxins are free to diffuse within the cell body with lateral diffusion coefficients on the order of 10 -9 cm2/s. In contrast, lateral diffusion of sodium channels in the axon hillock is restricted, apparently in two different ways. Not only do sodium channels in these regions diffuse more slowly (10-1°-10 -H cm2/s), but also they are prevented from diffusing between axon hillock and cell body. No regionalization or differential mobilities were observed, however, for either tetramethylrhodaminephosphatidylethanolamine, a probe of lipid diffusion, or FITC-succinyl concanavalin A, a probe for glycoproteins. During the maturation of the neuron, the plasma membrane differentiates and segregates voltagedependent sodium channels into local compartments and maintains this localization perhaps either by direct cytoskeletal attachments or by a selective barrier to channel diffusion.

Using FRAP and mathematical modeling to determine the in vivo kinetics of nuclear proteins

“…Therefore, the estimation of a diffusion coefficient on a bounded domain can be inaccurate if an infinite domain is assumed in the analysis. The issue of FRAP experiments in bounded regions was also addressed by Angelides et al [19], who asserted the dependence of fluorescence recovery curves after photobleaching on the size and shape of the area available for diffusion. Specifically, they simulated fluorescence recovery curves on rectangular domains of different dimensions, obtaining in this way curves with different asymptotic behaviors (see [19] for details).…”

“…Moreover, if the FRAP recovery curve exhibited slow and fast phases, this behavior would be satisfactorily explained by Eq. (19).…”

“…Because FRAP can be performed with laser scanning confocal microscopes, this technique is the most widely employed and available approach for measuring the movement of molecules in living cells. Methods 29 (2003) [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] www.elsevier.com/locate/ymeth FRAP is a very simple technique used to measure the movement of fluorescent molecules. FRAP takes advantage of the fact that fluorescent molecules eventually lose their ability to emit fluorescence when exposed to repeated cycles of excitation and emission.…”

Pannexin1 and Pannexin3 Delivery, Cell Surface Dynamics, and Cytoskeletal Interactions

“…Typically, the size of the immobile fraction is dependent on the nature of the protein and the membrane microenvironment being assessed. For instance, the immobile fraction of sodium channels ranges from ϳ10% in the cell body to ϳ40% in the neurite terminals (52). Likewise, the mobile fraction of glycine receptors ranges from ϳ50% in the neuronal cell body to ϳ70% in the processes (54).…”

Sodium channels in dendrites of rat cortical pyramidal neurons.

“…33-35, but see ref. 36). Unless the anchoring mechanism was disrupted by the dissociation, somatic channels would not be expected to have sufficient lateral mobility to move through the membrane to the dendrites.…”