Abstrakt: |
We have explored the role of the recently discovered second messenger nicotinic acid adenine nucleotide phosphate (NAADP+)inCa2+swings that accompany the fertilization process in starfish oocytes. The injection of NAADP+deep into the cytoplasm of oocytes matured by the hormone 1‐methylad‐enine (1‐MA), mobilized Ca2+exclusively in the cortical layer, showing that the NAADP+‐sensitive Ca2+pool is restricted to the subplasma membrane region of the cell. At variance with this, InsP3initiated the liberation of Ca2+next to the point of injection in the center of the cell. The initial cortical Ca2+liberation induced by NAADP+was followed by a spreading of the Ca2+wave to the remainder of the cell and by a massive cortical granule exocytosis similar to that routinely observed on injection of InsP3. A striking difference in the responses to NAADP+and InsP3was revealed by the removal of the nucleus from immature oocytes, i.e., from oocytes not treated with 1‐MA. Whereas the Ca2+response and the cortical granule exocytosis induced by NAADP+were unaffected by the removal of the nucleus, the Ca2+response promoted by InsP3was significantly slowed. In addition, the cortical granule exocy‐tosis was completely abolished. When enucleated oocytes were fertilized, the spermatozoon still promoted the Ca2+wave and normal cortical exocytosis, strongly suggesting that the Ca2+response was mediated by NAADP+and not by InsP3. InsP3‐sensitive Ca2+stores may mediate the propagation of the wave initiated by NAADP+since its spreading was strongly affected by removal of the nucleus.—Lim, D., Kyozuka, K., Gragnaniello, G., Carafoli, E., Santella, L. NAADP+initiates the Ca2+response during fertilization of starfish oocytes. FASEB J.15, 2257–2267 (2001) |