title: Axonal adaptations to osmotic and ionic stress in an invertebrate osmoconformer (Mercierella enigmatica Fauvel). II. Effects of ionic dilution on the resting and action potentials.
abstract: The giant axon of this extreme euryhaline osmoconformer possess an unusual ability to produce action potentials of large amplitude over a wide range of ionic dilution when constant osmotic concentration is maintained by the addition of mannitol to the bathing medium. Ionic dilution under these circumstances causes a decline in the overshoot of the action potential (resulting largely from reduction in [Na+]o) and an appreciable axonal hyperpolarization (primarily as a result of decrease in [K+]O). This hyperpolarization tends to compensate for the reduction in the extent of the overshoot and so maintains the amplitude of the sodium-mediated action potentials during isosmotic dilution of the bathing medium. The axonal hyperpolarization also appears to reduce sodium inactivation so as to maintain a rapid rate of rise of the action potential despite drastic reduction in the ionic concentration of the bathing medium. Prolonged exposure to reduced ionic concentrations appears to induce a ouabain sensitive reduction in intracellular sodium concentration which increases the sodium gradient across the axon membrane during isosmotic dilution of the external medium.
mesh_terms: D000200:Action Potentials; D000818:Animals; D001369:Axons / Q000502:physiology*; D008564:Membrane Potentials; D009995:Osmosis; D011077:Polychaeta / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D012828:Silicones / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D012828:Silicones; D012965:Sodium Chloride; D012964:Sodium; D011188:Potassium