Sperm's quick calcium response

Some free-swimming sperm detect the presence of an egg through chemotactic signals and respond by altering their swimming trajectory. On page 725, Wood et al. show that intact sea urchin sperm respond not to overall increases in intracellular Ca²⁺ levels, as previously thought, but to rapid changes in Ca²⁺ concentration. Ca²⁺ entry into the flagella is biphasic, with a fast and slow phase, but only the initial fast influx affects sperm trajectory.

Studies on demembranated sperm indicated that the cells change direction by asymmetrical bending of their flagella in response to overall Ca²⁺ increases and that cGMP signaling was involved. But until now scientists didn't have the tools to watch the process in real time in intact cells.

Using a...