Fowl (Gallus domesticus) Sperm Motility Depends Upon Mitochondrial Calcium Cycling Driven by Extracellular Sodium1

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.