Relationship Between Intracellular Calcium, Energy Metabolism, and Motility of Ram Sperm

Abstract

Collective sperm motility is characterized in terms of periodic aggregation or cooperation among cells, which are seen under a microscope as a continuous wave motion. In this study, sperm motility that was made dependent on mitochondrial activity (glycolysis inhibited) was significantly inhibited by mM exogenous calcium while glycolytic-dependent (mitochondrial respiration inhibited) motility was not inhibited under these conditions. At intracellular Ca²⁺ above 400 nM, sperm motility was inhibited independently of the source of ATP. At [Ca²⁺]i of-110 nM, mitochondrial- or glycolytic-dependent motility showed 75 or 0% inhibition, respectively, indicating higher sensitivity of mitochondrial-dependent motility to [Ca²⁺]i in comparison to glycolytic-dependent motility. Under the latter conditions, intracellular level of ATP was reduced by 16% only, indicating that the 75% inhibition of mitochondrial-dependent motility was not due to reduction in ATP. The inhibition of mitochondrial-dependent motility by mM extracellular Ca²⁺ can be prevented by incubating the cells at pH 6.5 instead of 7.6. At pH 7.6, calcium probably interacts with negative sites on the cell surface and interferes in cell-to-cell interactions, which are important to achieve collective motility. At more acidic pH (6.5) these negative sites are probably protonated; thus Ca²⁺ cannot interact with them and no inhibition of motility could be seen. Glycolytic-dependent motility was not inhibited by extracellular Ca²⁺, since the pH of the medium becomes acidic under these conditions. Like Ca²⁺, mersalyl, which interacts with Ca²⁺ binding sites on the cell surface, showed significant inhibition of mitochondrial-dependent motility without any effect on glycolytic-dependent motility. Collective motility was directly correlated with fertility. These data are significant for establishing better conditions for spermatozoa treatment when artificial insemination or in vitro fertilization is concerned.

Key Words:

• spermatozoa
• motility
• calcium