Calcium and a Fucose-Sulfate-Rich Polymer Regulate Sperm Cyclic Nucleotide Metabolism and the Acrosome Reaction1

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Abstract
A fucose-rich factor (FS-1) purified from the jelly coat of sea urchin eggs increased the rate of 45 Ca2+ accumulation, elevated cyclic AMP (cAMP) concentrations, and induced the acrosome reaction in sea urchin spermatozoa. The factor contained approximately 40% fucose and 36% sulfate, by weight, and its apparent molecular weight was in excess of 5 × 106. The elevation of cAMP concentrations, activation of adenylate cyclase and induction of the acrosome reaction by FS-1 all required the presence of Ca2+ in the extracellular medium, with half-maximal responses at 4–5 mM Ca2+ in all cases. In the presence of 9.6 mM Ca2+, the addition of D-600 or verapamil (100 μM) to spermatozoa at the same time as the factor completely blocked the effects of the factor. Increasing the extracellular concentration of Ca2+ to 40 mM could overcome the D-600 or verapamil inhibition. If D-600 or verapamil were added 20–50 sec after the factor, the drugs were no longer able to inhibit the activation of adenylate cyclase, the elevation of cAMP concentrations, or the induction of the acrosome reaction. FS-1 also failed to affect these three parameters in the presence of 1 μM trifluoperazine, a drug that effectively blocked 45Ca2+ uptake. Nigericin, which increased 45Ca2+ accumulation and induced the acrosome reaction in the absence of added factor, also activated the sperm adenylate cyclase. In attempts to determine the mechanism of Ca2+ activation, adenylate cyclase was solubilized with Triton X-100 and separated from detectable calmodulin on phenyl-Sepharose columns. Neither added Ca2+ nor calmodulin, however, activated the calmodulin-deficient, but detergent-solubilized enzyme. Thus, although adenylate cyclase appears to be regulated by a Ca2+-dependent event, it is not clear if a Ca2+-calmodulin complex serves as the mediator of the Ca2+ effect.