Fig. 6. Mutant S13A cells respond to a sequence of simulated temporal waves of cAMP generated in the absence of spatial gradients by increasing and decreasing velocity in a manner similar to wild-type JH10 cells. The instantaneous velocity is plotted as a function of time for a representative JH10 cell (A) and a representative S13A-1 cell (B) during four simulated waves. The estimated cAMP concentration, measured in dye experiments (Wessels et al., 2000b), is presented as a function of time through the four waves. Note that the velocity of neither JH10 nor S13A-1 cells increases in the front of the first simulated wave, a result previously reported for wild-type cells (Varnum et al., 1985). Instantaneous velocity was measured at 5 second intervals. Instantaneous velocity plots were smoothed 10 times with Tukey windows of 10, 20, 40, 20 and 10. Results similar to those for the representative JH10 and S13A-1 cells were obtained for nine additional cells of each respective cell line. Results similar to those for S13A-1 cells were obtained with S13A-2 cells.