The extra influx and efflux of radioactive Na and K associated with nerve impulses was measured. At 20-25°C the influx is Na, 4.8; K, 0.2 p moles/cm2 impulse. The fraction lost/impulse is Na, 6 x 10-6; K, 0.8 x 10-6 impulse-1. These may be expressed as equivalent fluxes (equivalent influx = influx/conc. outside). The equivalent fluxes are Influx Na, 1.1; K, 2; Efflux Na, 6.5; K, 0.8 all in 10-8 cm/impulse. If the ions are freely diffusing through the membrane the ratio of these equivalent fluxes should be related to the average potential during the fluxes by V = (kT/e) ln ratio. The potentials calculated by this formula are for Na, +44 mV; for K, -25 mV (outside potential = 0). The peak of the action potential is about +40 mV so the average potential during the fluxes must be somewhat less. This suggests that Na is not simply diffusing down its electrochemical gradient. The value for K seems appropriate since the bulk of the potassium movement is thought to occur during the repolarization phase of the action potential. The single file model (Hodgkin and Keynes, 1955) could help explain the sodium data but would be a poorer explanation for potassium.
|Original language||English (US)|
|Pages (from-to)||No. 1528|
|Issue number||5 II|
|State||Published - Jan 1 1974|
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