Figure 4.

Mobilisation of stores Ca²⁺ at the sperm neck/midpiece leads to modulation of flagellar activity. a shows phase image of immobilised, Oregon Green BAPTA 1-labelled human sperm. b-g are a series of pseudocoloured fluorescence images (taken at 10 s intervals) of the same cell during a Ca²⁺ transient induced by treatment with progesterone. The cell was bathed in medium with no added Ca²⁺. Ca²⁺ is liberated at the sperm neck and spreads into both the posterior head and the flagellum. During the Ca²⁺ peak a pronounced bend occurs in the proximal flagellum (e) and excursion of the flagellum increases (d,f).