CYCLIC ADP-RIBOSE SIGNALING IN SEA-URCHIN GAMETES - METABOLISM IN SPERMATOZOA

The molecular mechanism that initiates Ca2+ signaling in sea urchin eg g fertilization has not yet been clarified. To determine whether sea u rchin sperm may generate and possibly supply cyclic ADP-ribose (cADPR) as a Ca2+-releasing factor in the course of sea urchin egg fertilizat ion, we determined cADPR content and the capacity for cADPR synthesis in sea urchin sperm. cADPR content was determined using the sea urchin egg homogenate Ca2+-release bioassay combined with high-performance l iquid chromatography (HPLC). We found that sperm homogenates synthesiz ed cADPR. from beta-NAD but did not synthesize cADPR when alpha-NAD wa s tile substrate. The identity of cADPR generated by sperm homogenates was verified by HPLC analysis, use of specific Ca2+-release antagonis ts, and homologous desensitization of the sea urchin egg homogenate Ca 2+-release bioassay. The ambient content of cADPR was similar to 0.3 n mol cADPR/g wet wt sea urchin sperm. Our results show that; sperm can synthesize cADPR and that they contain cADPR levels comparable to othe r tissues.