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 inhi bit sperm motility, but little is known about the effect of different calci um activities close to the physiological range. Therefore, we investigated whether raising calcium activities within the submicromolar range would inh ibit the motility of demembranated human spermatozoa. Spermatozoa were deme mbranated with Triton X-100 and motility was measured objectively by comput er assisted semen analysis. Motility, reactivated by 1 mol adenosine 5'-tri phosphate (A TP)/L, was short lived, with maximum activity only sustained f or about 1 min. Reactivated motility was not affected by 50 mu mol cAMP/L. The amplitude of lateral head displacement was significantly greater at roo m temperature than at 37 degreesC, but there were no significant difference s between the percentage of sperm motile or their velocity at the two tempe ratures. The calcium buffer 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraac etic acid (BAPTA) at 1 mmol/L was included in the demembranation-reactivati on medium, and free calcium ion activities were calibrated using the fluore scent calcium probe Fura-2. Calcium ion activities of greater than or equal to 500 nmol/L significantly inhibited the percentage of demembranated-reac tivated spermatozoa that were motile, and the velocity and lateral head dis placement of these cells. The range of intracellular calcium activities in spermatozoa from 24 cryopreserved ejaculates was 110-534 nmol/L; roughly tw ice the value in fresh spermatozoa. Therefore, calcium ion activities in th e range observed in cryopreserved spermatozoa can inhibit the activity of d emembranated human spermatozoa.