Figure 6. Na⁺-dependent changes of the MT system.

(a) MTs in cells were largely frozen after 5 min 10 mM pH3 HA bath and 3 min in the wash solution, such as 5 mM pH7.4 Na⁺/HEPES buffer or 5 mM NaCl solution (black arrowheads). In contrast, growing MTs with a comet (white arrowheads) returned if the wash buffer lacked Na⁺, such as 5 mM K⁺/HEPES buffer, 5 mM KCl solution, or ddw. (b) Thick MTs in cells resuspended in 21 mM Na⁺/EGTA for 5 min or 10 min (left panel), contrary to comets in cells in 21 mM K⁺/EGTA (right panel). Thick MTs were still growing after 5 min incubation but static after 10 min incubation. (c) High [Na⁺]_ex, without pre-exposure to HA, was sufficient to alter comet patterns. Contrary to typical comets in cells resuspended in the HEPES buffer with 5 mM Na⁺, long comets were thick in cells resuspended in 55 mM Na⁺ for 5 min (panel I). Normalized linescans confirmed little tapered intensity (panel II, n = 36 comets from 11 cells in 5 mM Na⁺; n = 13 comets from 4 cells in 55 mM Na⁺). As shown in the range of speed (panel III), long comets were moving, and the mean speeds of short and long comets were significantly different (panel IV, n = 51 from 11 cells in 5 mM Na⁺; n = 18 from 4 cells in 55 mM Na⁺) (p<0.05). (d) Two representative cells after 5 min in 150 mM Na⁺/HEPES. Some cells still retained a few thick MTs (cell I). Some only had static EB1 signals at the BB area (cell II, arrowhead). Scale bars, 5 μm.