Role of sodium bicarbonate on the initiation of sperm motility in the Japanese eel [Anguilla japonica]

In order to find out the role of sodium bicarbonate (NaHC03) on the initiation of sperm motility in the Japanese eel Anguilla japonica, interactions were investigated between NaHCO3 and various reagents (KE+ channel blocker 4-aminopyridine [4-AP], ammonium chloride [NH4Cl], sodium acetate and calcium chloride (CaCl2)) that could regulate internal factors (intracellular KE+, intracellular pH [[pH]i] and intracellular CaE2+) in sperm motility. Contradictory effects of NaHC03 were observed (i.e. an inhibitory effect when 4-AP was absent and a promoting effect when 4-AP was present). Sodium bicarbonate inhibited the initiation of sperm motility in the Japanese eel. However, NaHCO3 restored the motility of immotile sperm that 4-AP inhibited. The inhibitory effect of NaHC03 disappeared with the addition of NH4CI, which raised [pH]i, but the promoting effect was not affected by [pH]i. Although NaHCO3 recovered motility in the presence of 4-AP, this recovery was also observed with the addition of CaCI2 instead of NaHCO3. In the initiation of sperm motility in the Japanese eel, two roles for NaHC03 are suggested: an inhibitory role relating to the regulation of [pH]i and a promoting role relating to the uptake of another initiation factor, which could be CaE2+.