(Downloading may take up to 30 seconds.
If the slide opens in your browser, select File -> Save As to save it.)
Click on image to view larger version.
Fig. 7. Effects of osmolarity and myosin II deficiency on directionality of cells during chemotaxis. Representative contour traces of chemotaxing cells at 5-second intervals are shown. (A) AX2 without sorbitol during 535 seconds. Bar, 10 µm. (B) AX2 with 100 mM sorbitol during 525 seconds. (C) A myosin-II-null cell without sorbitol during 465 seconds. (D) A myosin-II-null cell with 100 mM sorbitol during 995 seconds. The red dots at the upper right show the source of the chemoattractant, cAMP. (E) Effects of sorbitol on the velocities of chemotaxing cells. Centroid velocities of cells starved for 8-9 hours were assayed in the absence (random) or presence (chemotaxis) of a capillary filled with 200 µM cAMP. Values are means ± s.e.m. Effects of sorbitol were significant for wild-type cells without or with a cAMP source, but less significant for myosin-II-null cells with a cAMP source. At high osmolarity, the difference between wild-type and myosin-II-null cells in the presence of cAMP was insignificant. (F) For a cell i with the centroid located at a point C(t) at time t moving to a point C'(t+
) after time period of in the gradient of chemoattractant emitted from the source placed at point N, the chemotaxis index was defined as the mean of cos
weighted by |
|, with designating the angle between and 
, i.e.
CI_|<|i|>|(|<|\tau|>|)=\frac|<||<|\sum_|<|t=0|>|^|<|T_|<|i|>|-|<|\tau|>||>||>|| |cos|<|\phi|>||>||<||<|\sum_|<|t=0|>|^|<|T_|<|i|>|-|<|\tau|>||>||>||||>|. |
The average function CI() was calculated with home-developed Perl scripts for a cell population, weighted by the data length Ti-. (G) Chemotaxis index shown as a function of time. Wild-type (WT; red and green) and myosin-II-null (MII-; blue and orange) cells in buffer without (SB; red and blue) or with (HI; green and orange) 100 mM sorbitol. The averages of the chemotaxis indices from 56 (red), 42 (green), 44 (blue), and 54 (orange) cells are shown. The line-width represents the means ± s.e.m.
