Fertilization acid release in Urechis eggs. II. The stoichiometry of Na+ uptake and H+ release.
We tested the hypothesis that Na+ uptake and H+ release at fertilization of Urechis eggs might occur via a Na+:H+ exchange. Previous studies have shown that (1) Na+ uptake is proportional to the number of entering sperm in seawater with or without lowered Na+ and (2) H+ release is proportional to external pH. Therefore, to determine if Na+ uptake and H+ release are always proportional, we determined the effect of polyspermy on H+ release in natural and low Na+ seawater and the effect of external pH on Na+ uptake and release. Na+ uptake and H+ release do not covary in a manner consistent with a Na+:H+ exchange. H+ release under most conditions was manner consistent with a Na+:H+ exchange. H+ release under most conditions was independent of the number of sperm/egg and in low Na+ seawater was at most 53 +/- 16% of that in natural seawater. In contrast, Na+ uptake in low Na+ seawater can be more than in natural seawater (Jaffe et al., J. Gen. Physiol. 73, 469-492, 1979). In natural seawater Na+ uptake exceeded H+ release; at pH 7 Na+ uptake was 2 pmol/egg, but there was no H+ release. Since Na+ release did not increase at fertilization at pH 7, neither Na+:Na+ nor Na+:H+ exchange could account for the Na+ uptake. An alternate hypothesis is suggested: Na+ uptake is primarily via the channels responsible for the fertilization potential, while H+ release is by another route that is affected by the membrane potential during the fertilization potential.
D000818:Animals; D000845:Annelida / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism*; D005260:Female; D005306:Fertilization; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D010063:Ovum / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D013084:Sperm-Ovum Interactions
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium