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We report an ion channel in the plasma membrane of unfertilized oocytes of the ascidian Ciona intestinalis that is directly gated by the second messenger ADP-ribose. The ion channel is permeable to Ca2+ and Na+ and is characterized by a reversal potential between 0 and +20 mV and a unitary conductance of 140 pS. Preinjection of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) or antagonists of intracellular Ca2+ release channels into oocytes did not inhibit the ADP-ribose current, demonstrating that the channel is activated in a Ca2+-independent manner. Both the fertilization current and the current induced by the injection of nicotinamide nucleotides are blocked by nicotinamide, suggesting that the ADP-ribose channel is activated at fertilization in a nicotinamide-sensitive manner. These data suggest that ascidian sperm trigger the hydrolysis of nicotinamide nucleotides in the oocyte to ADP-ribose and that this mechanism is responsible for the production of the fertilization current.

Original publication




Journal article


The American journal of physiology

Publication Date





C1277 - C1283


Stazione Zoologica "Anton Dohrn," 80121 Naples, Italy.


Oocytes, Animals, Ciona intestinalis, Sodium, Calcium, Egtazic Acid, Niacinamide, NAD, NADP, Adenosine Diphosphate Ribose, Ion Channels, Chelating Agents, Patch-Clamp Techniques, Cell Membrane Permeability, Ion Channel Gating, Membrane Potentials, Electric Conductivity, Fertilization, Female, In Vitro Techniques