Calcium fractions in seminal plasma and functional properties of human spermatozoa

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Abstract
The concentration of ionized calcium [Ca2+] was reproducibly determined in human seminal plasma with a Ca sensitive electrode (Orion Space Stat 20). Dilution of the seminal plasma gave a linear decrease in free Ca concentration. Freezing and thawing or storage of the seminal plasma under anaerobic conditions did not influence the level of ionized Ca. Storage under aerobic conditions gave a temperature dependent decrease in Ca2+ which paralleled a spontaneous increase in pH. The mean concentration of ionized Ca (measured after a standardized air exposition) was 0.17 mM .+-. 0.05 (SD) (range 0.09-0.29 mM). The Ca2+ level was not correlated to the total Ca concentration or to markers for prostatic (Zn) or seminal vesicular (fructose) secretions. There were, however, more motile spermatozoa in semen samples with an ionized Ca level less than the average (0.17 mM) than in semen samples with a higher Ca2+ level (53.8% .+-. 8.4, no. = 17 vs. 45.0% .+-. 12.8, no. = 15, respectively, P < 0.05). The percentage live spermatozoa was also higher (62.4% .+-. 10.4, no. = 17 vs. 50.7% .+-. 14.2, no. = 15, P < 0.01) in the semen samples with a low [Ca2+]. Spermatozoa in the low [Ca2+] group did also exhibit a better progressive motility than spermatozoa in the high [Ca2+] group (P < 0.05). It is suggested that the low level of ionized Ca in seminal plasma is of importance for motility of human spermatozoa and that the transfer of spermatozoa from a high Ca2+ in the epididymis to the low levels in accessory sex glands secretion might be of significance for activation of spermatozoa upon ejaculation.

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