title: Action potential prolongation: an effect of physostigmine (eserine) upon Retzius cells in the leech C.N.S.
abstract: Physostigmine (PHY; eserine) prolongs the action potentials in the Retzius cells within leech ganglia to about 800 ms. The effect was reversible and occurred at concentrations of 1-10 mM which are several orders of magnitude greater than those required to inhibit cholinesterase. The prolonged action potentials showed an early, spike-like depolarization followed by a plateau. The initial depolarization exhibited a strong dependence on external Na+ while the amplitude of the plateau had somewhat less Na+ dependence: 52 and 24 mV/decade, respectively. The duration of the plateau was increased by elevating Na+ and decreased by elevating Ca2+. Increasing the action potential frequency, by intracellular stimulation, decreased both the duration and amplitude of the plateau. Neostigmine, di-isopropylphosphofluoridate, and acetylcholine did not prolong RZ action potentials. Thus, the membrane effects of physostigmine appear to be independent of any inhibition of cholinesterase or accumulation of acetylcholine.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000502:physiology; D005724:Ganglia / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D007531:Isoflurophate / Q000494:pharmacology; D007865:Leeches / Q000502:physiology*; D008839:Microelectrodes; D009388:Neostigmine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D010830:Physostigmine / Q000494:pharmacology*; D012964:Sodium / Q000502:physiology
chemical_list: D007531:Isoflurophate; D009388:Neostigmine; D012964:Sodium; D010830:Physostigmine; D000109:Acetylcholine; D002118:Calcium