title: Primary and secondary messengers in the activation of ascidian eggs.
abstract: Two early events of activation in the ascidian egg, the surface contraction and the fertilization current, were studied. Ca ionophore induces contraction without generating a fertilization current, whereas microinjection of IP3 or soluble fractions of homogenized spermatozoa trigger both a contraction and a current. This suggests that the primary trigger of activation in ascidian eggs is a soluble component of spermatozoa that may be released into the egg subsequent to gamete fusion. IP3, or other intermediates in phosphoinositide metabolism, is a putative second messenger that activates fertilization channels directly (probably a Ca-independent process), and subsequently induces surface contraction by releasing Ca from intracellular stores.
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000502:physiology; D002938:Ciona intestinalis / Q000502:physiology*; D005306:Fertilization; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials; D010063:Ovum / Q000187:drug effects / Q000502:physiology*; D012617:Sea Urchins; D013094:Spermatozoa / Q000502:physiology; D013403:Sugar Phosphates / Q000494:pharmacology*; D014561:Urochordata / Q000502:physiology*
chemical_list: D007295:Inositol Phosphates; D013403:Sugar Phosphates; D000001:Calcimycin; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium