Timing of sperm capacitation varies reproducibly among men

Sperm must mature functionally in the process of capacitation to become able to fertilize. Capacitation depends on membrane lipid changes, and can be quantitatively assessed by redistribution of the ganglioside G(M1), the basis of the Cap-Score sperm function test. Here, differences in Cap-Score were compared among and within men at two time points. Ejaculates were liquefied, washed, and incubated for 3 hr under capacitating (Cap) conditions, then fixed and analyzed immediately (Day0); after being incubated 3 hr under Cap conditions then maintained 22-24 hr in fix (Day1-fix); or after 22-24 hr incubation under Cap conditions prior to fixation (Day1). In all cases, a light fixative previously shown to allow membrane lipid movements was used. Day1-fix and Day1 Cap-Scores were greater than Day0 (p < 0.001; n = 25), whereas Day1-fix and Day1 Cap-Scores were equivalent (p = 0.43; n = 25). In 123 samples from 52 fertile men, Cap-Score increased more than 1SD (7.7; calculated previously from a fertile cohort) from Day0 to Day1-fix in 44% (54/123) of the samples. To test whether timing of capacitation was consistent within an individual, 52 samples from 11 fertile men were classified into either early or late capacitation groups. The average capacitation group concordance within a donor was 81%. Median absolute deviation (MAD; in Cap-Score units) was used to assess the tightness of clustering of the difference from Day0 to Day1-fix within individuals. The average (2.21) and median (1.98) MAD confirmed consistency within individuals. Together, these data show that the timing of capacitation differed among men and was consistent within men.