A relationship between extracellular Ca 2, fowl sperm phospholipase A2 activity, long-chain acylcarnitine content, and motility was demonstrated in previous work. Sperm motility appeared to depend upon Na -dependent Ca 2 cycling when sperm were incubated at body temperature without glucose. In the present work, motility decreased as a function of time when sperm were incubated in 2 mM Ca 2 prepared with either buffered isotonic sucrose or LiCl. However, this effect was less pronounced in the case of LiCl. The sparing effect of Li was attributed to the mitochondrial Na /Ca 2 exchanger. Motile concentration decreased exponentially in response to micromolar concentrations of CGP 37157, a specific inhibitor of the mitochondrial Na /Ca 2 exchanger. KB-R7943 mesylate, an inhibitor of the reverse mode of the Na /Ca 2 exchanger, prevented re-initiation of motility when exogenous Ca 2 was added to sperm rendered immotile by incubation with 1,2-bis-(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid, a high-affinity Ca 2 chelator. The presence of voltage-gated Ca 2 channels was confirmed by the effect of nifedipine on motile concentration. Neither motile concentration nor straight line velocity was affected by either ouabain or orthovanadate, which inhibit Na -K ATPase and Ca 2-ATPase, respectively. In summary, we infer that 1) fowl sperm motility is dependent upon extracellular Ca 2 cycling through mitochondria; 2) such cycling is dependent upon extracellular Na ; and 3) fowl sperm conserve ATP by moving neither Na nor Ca 2 by active transport. Understanding the relationship between mitochondrial Ca 2 cycling and ATP production may be applicable to long-term semen storage.
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