Nitric oxide gates fertilization channels in ascidian oocytes through nicotinamide nucleotide metabolism.

In this paper we use the nitric oxide (NO) donor sodium nitroprusside to examine the response of the unfertilised oocyte of the ascidian Ciona intestinalis to nitric oxide. We show that the release of NO triggers an inward current that displays similar properties to the ascidian fertilisation current. Furthermore, the production of NO causes the release of intracellular calcium through a ruthenium-red sensitive mechanism. Our data suggest that these effects are due to the stimulation of nicotinamide nucleotide metabolism, but the active second messenger is not cyclic adenosine diphosphate ribose (cADPr). Finally, we show that NO production increases at fertilisation. The results suggest that ascidian sperm trigger the release of NO and this second messenger causes the breakdown of nicotinamide nucleotides leading to the production of a second messenger which induces the fertilisation current and may assist in the production of the increase in calcium.