Steady-state contribution of the sodium pump to the resting potential of a molluscan neurone.
1. The electrogenic contribution of the Na(+)-K(+) exchange pump to the membrane potential of the Anisodoris giant neurone (G cell) was examined under steady-state and Na(+) loaded conditions.2. The membrane potential was variable for the first 1-4 hr after impalement, but, in the absence of experimental manipulation, remained constant thereafter. The average membrane potential for ten cells maintained at 11-13 degrees C and measured 5-36 hr after impalement was 55.8 +/- 1.0 mV (S.E. of mean).3. Low concentrations of external ACh caused a reversible increase in membrane Na(+) conductance. Brief exposure to ACh proved a fast and reversible technique to load the cell with Na(+) ions, and transiently stimulate the electrogenic Na(+) pump.4. In ten cells maintained from 5 to 36 hr at 11-13 degrees C the reduction in membrane potential produced by inhibition of the Na(+) pump with ouabain was remarkably constant between cells and averaged + 9.7 mV.5. Cells maintained under steady-state conditions (at 11-13 degrees C) for extended periods of time were shown to be relatively insensitive to changes in temperature and to small changes in external K(+).6. It is estimated that the Na(+)-K(+) exchange pump contributes approximately - 10 mV to the steady-state resting potential of the G cell, and that two Na(+) ions are extruded for every K(+) ion transported into the cell per pump cycle.
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D003470:Culture Media; D066298:In Vitro Techniques; D008564:Membrane Potentials; D008974:Mollusca / Q000502:physiology*; D009474:Neurons / Q000378:metabolism* / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D013696:Temperature
D003470:Culture Media; D010042:Ouabain; D012964:Sodium; D000109:Acetylcholine; D011188:Potassium