Figure 3.

Iontophoretic injection of controlled amounts of calcium during early anaphase produces a clear effect on chromosome motion. In A and B, the injection needle was inserted into the mid plane of the cell, whereas in C, it was inserted into the spindle pole. The microinjection needle contained 20 mm CaCl₂ and 100 mm KCl. The magnitude of the current was then varied in order to produce the desired level of calcium. A, Application of positive current of 1 nA for 10 s, which produces an increase in calcium to approximately 1 µm, causes the chromosomes to increase their rate of motion from 1.1 to 2.1 µm min⁻¹ for approximately 20 s. B, However, application of 2 nA for 10 s causes a brief slowing of chromosome motion. C, Injection of calcium at 2 nA for 10 s to one of the spindle poles causes a brief slowing of chromosomes to the proximal pole while simultaneously accelerating motion to the distal pole. From Zhang et al. (1990b).