The motility of demembranated human spermatozoa is inhibited by free calcium ion activities of 500 nmol/L or more

A number of studies have demonstrated that high calcium ion activities inhibit sperm motility, but little is known about the effect of different calcium activities close to the physiological range. Therefore, we investigated whether raising calcium activities within the submicromolar range would inhibit the motility of demembranated human spermatozoa. Spermatozoa were demembranated with Triton X-100 and motility was measured objectively by computer assisted semen analysis. Motility, reactivated by 1 mol adenosine 5'-triphosphate (AlphaTauP)/L, was short lived, with maximum activity only sustained for about 1 min. Reactivated motility was not affected by 50 micromol cAMP/L. The amplitude of lateral head displacement was significantly greater at room temperature than at 37 degrees C, but there were no significant differences between the percentage of sperm motile or their velocity at the two temperatures. The calcium buffer 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) at 1 mmol/L was included in the demembranation-reactivation medium, and free calcium ion activities were calibrated using the fluorescent calcium probe Fura-2. Calcium ion activities of > or =500 nmol/L significantly inhibited the percentage of demembranated-reactivated spermatozoa that were motile, and the velocity and lateral head displacement of these cells. The range of intracellular calcium activities in spermatozoa from 24 cryopreserved ejaculates was 110-534 nmol/L; roughly twice the value in fresh spermatozoa. Therefore, calcium ion activities in the range observed in cryopreserved spermatozoa can inhibit the activity of demembranated human spermatozoa.