The pH dependence of motility and the acrosome reaction of guinea pig spermatozoa

The effect of pH on both motility and the acrosome reaction of guinea pig spermatozoa was examined by transferring fully capacitated spermatozoa from Ca2+ ‐free medium to Ca2+ ‐containing media with various pH values (8.2, 7.5, 7.0, 6.7, 6.4, and 6.1). When transferred to media of pH 7.5 or 8.2, the spermatozoa underwent their acrosome reactions to the maximum level within 15–20 min. Acrosome‐reacted spermatozoa were vigorously motile. The intensity of sperm motility and the incidence of the acrosome reaction declined with decreasing pH values. At pH 6.1, the motility of all the spermatozoa quickly became very weak. No acrosome reactions occurred at this low pH. The inhibition of motility and the acrosome reaction at pH 6.1 was reversed by transferring the spermatozoa back to the alkaline medium unless they were exposed to this low pH for longer than 3 hr. The inhibition of the acrosome reaction at low pH values (other than 6.1) was counteracted to some extent by increased concentrations of Ca2+ (4–10 mM). Possible mechanisms by which low pH reversibly inhibits sperm motility and the acrosome reaction are discussed.