Calcium fractions in seminal plasma and functional properties of human spermatozoa

The concentration of ionized calcium [Ca++] was reproducibly determined in human seminal plasma with a calcium sensitive electrode (Orion Space Stat 20). Dilution of the seminal plasma gave a linear decrease in free calcium concentration. Freezing and thawning or storage of the seminal plasma under anaerobic conditions did not influence the level of ionized calcium. Storage under aerobic conditions gave a temperature dependent decrease in CA++ which parallelled a spontaneous increase in pH. The mean concentration of ionized calcium (measured after a standardized air exposition) was 0.17 mM +/- 0.05 (SD) (range 0.09-0.29 mM). The Ca++ level was not correlated to the total calcium concentration or to markers for prostatic (zinc) or seminal vesicular (fructose) secretions. There were, however, more motile spermatozoa in semen samples with an ionized calcium level less than the average (0.17 mM) than in semen samples with a higher Ca++ level (53.8% +/- 8.4, N = 17 vs 45.0% +/- 12.8, N = 15, respectively, p less than 0.05). The percentage live spermatozoa was also higher (62.4% +/- 10.4, N = 17 vs 50.7% +/- 14.2, N = 15, p less than 0.01) in the semen samples with a low [Ca++]. Spermatozoa in the low [Ca++] group did also exhibit a better progressive motility than spermatozoa in the high [Ca++] group (p less than 0.05). It is suggested that the low level of ionized calcium in seminal plasma is of importance for motility of human spermatozoa and that the transfere of spermatozoa from a high Ca++ in the epididymis to the low levels in accessory sex glands secretion might be of significans for activation of spermatozoa upon ejaculation.