title: Optical evidence for calcium-action potentials in early embryonic precontractile chick heart using a potential-sensitive dye.
abstract: Using an optical method for monitoring membrane potential, spontaneous action potentials in the 7- to 9-somite embryonic precontractile chick hearts were measured. The optical action potential in the 7- to 9-somite embryonic heart was lacking 'phase 0' and 'phase 1' attributable to the fast Na+ current. The embryonic precontractile heart continued to generate spontaneous action potentials in a Na+-free solution or in the presence of tetrodotoxin. Such an action potential was blocked by adding Co2+, Mn2+, Ni2+, La3+, D-600 or GEDTA, and the frequency, the amplitude, and the rate of rise of the spontaneous action potentials depended closely upon the external Ca2+ concentration; reducing the external Ca2+ concentration resulted in suppression of the spontaneous excitability. From the above results, we concluded that the spontaneous action potential in the early phases of cardiogenesis is characterized as a Ca2+-dependent action potential.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002412:Cations / Q000494:pharmacology; D002642:Chick Embryo; D006321:Heart / Q000196:embryology* / Q000502:physiology; D012964:Sodium / Q000502:physiology
chemical_list: D002412:Cations; D012964:Sodium; D002118:Calcium