Optical studies on the kinetics of the sodium pump in mammalian non-myelinated nerve fibres.
1. A study has been made of the changes in the fluorescence of desheathed rabbit cervical vagus nerves that occur during and after electrical stimulation of its non-myelinated fibres.2. Stimulation for 5 sec at 30 shocks/sec produces a maximal decrease, of about 1% of the resting fluorescence. Stimulation for less than 0.5 sec fails to produce responses visible above the inherent noise in the recording system.3. A pharmacological dissection (with ouabain, metabolic inhibitors, and calcium) has revealed four phases of fluorescence change:(a) under conditions where the sodium pump is functioning, there is a prolonged decrease in the fluorescence following electrical activity;(b) even in the absence of pumping the mere entry of sodium into the nerve causes an initial decrease in fluorescence;(c) the entry of calcium ions with electrical activity also causes an initial rapid decrease in fluorescence;(d) following these phases of decreased fluorescence there is a phase of increased fluorescence.4. These changes in fluorescence are related to changes in the NADH concentration in the nerve resulting from:(a) the splitting of ATP during sodium extrusion;(b) the initial binding of sodium to the sodium- and potassium-dependent ATPase, which is the sodium pump;(c) the stimulation of mitochondrial respiration by calcium that has entered during the spike; and(d) an increased glycogenolysis as a result of the calcium entry during activity.
D000200:Action Potentials; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D001369:Axons / Q000378:metabolism / Q000502:physiology*; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D004558:Electric Stimulation; D005453:Fluorescence; D006003:Glycogen / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011817:Rabbits; D012119:Respiration / Q000187:drug effects; D012964:Sodium / Q000378:metabolism*; D013268:Stimulation, Chemical; D014630:Vagus Nerve / Q000502:physiology
D000963:Antimetabolites; D010042:Ouabain; D000255:Adenosine Triphosphate; D006003:Glycogen; D012964:Sodium; D000251:Adenosine Triphosphatases; D002118:Calcium