A calcium-activated sodium conductance produces a long-duration action potential in the egg of a nemertean worm.
1. The egg of the nemertean worm Cerebratulus lacteus produced an action potential having a duration of about 9 min. We investigated the ionic conductances which accounted for this long-duration action potential. 2. The peak of the action potential was about +50 mV and depended on extracellular Ca2+, while the plateau potential was about +25 mV and depended on extracellular Na+. 3. Under voltage-clamp conditions, depolarization produced two temporally separate inward currents: a fast current which reached a peak at about 10 ms, and a slow current which took up to 1 min to reach its peak and lasted for several min. 4. The fast current was independent of extracellular Na+, but was blocked by removal of extracellular Ca2+. 5. The slow current was not seen when extracellular Na+ was replaced by choline+ or K+. 6. The slow current did not develop in Ca2+-free sea water, and was reduced to about half if Ca2+ was removed after the current had been initiated. 7. Microinjection of EGTA blocked the slow current, and reduced the action potential duration to about 1 min. 8. We concluded that a voltage-activated Ca2+ conductance produced the peak of the action potential, while a Ca2+-activated Na+ conductance produced its plateau.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002794:Choline / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects; D010063:Ovum / Q000502:physiology*; D010986:Platyhelminths / Q000502:physiology*; D012964:Sodium / Q000502:physiology*; D013997:Time Factors
D007473:Ion Channels; D004533:Egtazic Acid; D012964:Sodium; D002794:Choline; D002118:Calcium