Temperature-Dependent Immobilization and Restoration of Fowl Sperm Motility Caused by Intracellular Free Calcium

Abstract

Fowl spermatozoa maintained vigorous movement at 30°C with or without Ca²⁺. In contrast, the motility was reversibly inhibited at 40°C without Ca²⁺, but could be immediately restored by the addition of Ca2⁺. However, the addition of verapamil, a specific Ca²⁺ channel blocker, before the addition of Ca²⁺, could not obtain fully motile spermatozoa at 40°C . Under these conditions, the intracellular free Ca²⁺ concentration was lower than that of the control (no addition of verapamil), as measured by a fluorescent Ca²⁺ indicator, fura-2. The preparations of spermatozoa without Ca²⁺ were in-cubated at 30°C, and then transferred and incubated at 40°C . After that, they were re-incubated at 30°C again. During the second incubation at 30°C, high motility was obtained, even in the presence of verapamil. The addition of Sr²⁺, which appears to stimulate the release of Ca²⁺ from the mitochondria, was also effective for the stimulation of motility at 40°C, and induced a concomitant increase in the intracellular free Ca2⁺ concentrations. These results suggest that intracellular free Ca²⁺ play a pivotal role in regulating fowl sperm motility. Furthermore, it appears that fowl sperm mitochondria have a significant role in controlling intracellular free Ca²⁺ concentrations. This mech-anism, rather than Ca²⁺ fluxes through the plasma membrane, may be involved in the temperature-dependent immobilization and restoration of fowl sperm motility.