title: Intracellular sodium activity and the sodium pump in snail neurones.
abstract: 1. Recessed-tip Na(+)-sensitive micro-electrodes were used to measure [Na(+)](i) continuously in snail neurones for experiments lasting up to several hours. The average resting [Na(+)](i) in twenty-two cells was 3.6 mM.2. Inhibition of the Na pump by ouabain caused [Na(+)](i) to increase at an average rate of 0.54 m-mole/min. This corresponds to a passive influx of Na quantitatively similar to that observed in squid axons.3. Changing external K over the range 1-8 mM had little effect on [Na(+)](i), but K-free or 0.25 mM-K Ringer caused a rise in [Na(+)](i).4. Increasing membrane potential by up to 90 mV caused an increased influx of Na, but did not inhibit the pump.5. Reducing external Na caused a decrease in [Na(+)](i) but did not affect the pump rate at a given [Na(+)](i). The pump rate at low [Na(+)](i) was proportional to [Na(+)](i) minus a threshold value of about 1 mM.6. The Na pump appeared still to be electrogenic at subnormal rates of activity.7. It is concluded that, given sufficient external K, the rate of the Na pump depends principally on [Na(+)](i). Changes in external Na or membrane potential appear to affect the pump only indirectly, by changing the Na influx and thus [Na(+)](i).
mesh_terms: D000200:Action Potentials; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D008564:Membrane Potentials; D008839:Microelectrodes; D009474:Neurons / Q000032:analysis / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012908:Snails; D012964:Sodium / Q000032:analysis / Q000378:metabolism*
chemical_list: D010042:Ouabain; D012964:Sodium; D011188:Potassium