SPERM AND ITS SOLUBLE EXTRACT CAUSE TRANSIENT INCREASES IN INTRACELLULAR CALCIUM-CONCENTRATION AND IN MEMBRANE-POTENTIAL OF SEA-URCHIN ZYGOTES

Fertilization is known to initiate a transient increase of intracellul ar calcium concentration and an accompanying change of membrane potent ial in sea urchin eggs. If the fertilization membrane and hyaline laye r are removed, sperm can again enter fertilized eggs (refertilization) . We have found that Ca2+ and voltage transients were repeatedly induc ed in fertilized eggs during refertilization. Similar changes were als o obtained by external application of a soluble extract of sperm to fe rtilized eggs. This sperm extract caused no changes in unfertilized eg gs. The active factor in the sperm extract survives heating (100 degre es C, 10 min) and incubation with pronase. Its molecular weight is les s than 1300. (C) 1994 Academic Press, Inc.