title: A calcium-activated sodium conductance contributes to the fertilization potential in the egg of the nemertean worm Cerebratulus lacteus.
abstract: The fertilization potential of the egg of the nemertean worm Cerebratulus lacteus consisted of a rapid shift from a resting potential of about -65 mV to a peak of about +44 mV; the peak was followed by a positive plateau at about +24 mV, lasting an average of 80 min. Reduction of extracellular calcium reduced the peak of the fertilization potential, indicating that the peak resulted from a calcium conductance, while reduction of extracellular sodium reduced the plateau potential, indicating that the plateau resulted from a sodium conductance. Microinjection of ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) or 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)/CaBAPTA buffers, having a free calcium concentration of less than or equal to about 0.1 microM lowered the fertilization potential plateau. Injection of a BAPTA/CaBAPTA mixture with a free calcium concentration of about 1 microM resulted in a prolonged positive potential at the level of the fertilization potential plateau. These observations indicated that the fertilization potential of the Cerebratulus egg depended on a calcium-activated sodium conductance. The plateau potential was reduced little, if any, when calcium-free seawater was perfused through the bath during the fertilization potential; nor was it reduced in seawater containing cadmium. These observations suggested the possibility that intracellular calcium stores could be important in producing the fertilization potential.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D004533:Egtazic Acid / Q000494:pharmacology / Q000031:analogs & derivatives; D004553:Electric Conductivity; D005306:Fertilization; D007448:Invertebrates / Q000196:embryology / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D010063:Ovum / Q000502:physiology*; D012964:Sodium / Q000502:physiology
chemical_list: D004533:Egtazic Acid; D012964:Sodium; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium