Influence of Some Ions on the Membrane Potential of Ascaris Muscle

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Abstract
The influence of several ions on the membrane potential of the somatic muscle of Ascaris has been investigated by changing their concentration in the surrounding solution. When [K]o is increased at the expense of [Na]o leaving [Cl]o constant, the membrane potential is first seen to increase. [K]o higher than 45 mM reduces the membrane potential with a slope of 23 mv for a tenfold change in [K]o. However, when [K]o is increased keeping [Na]o and [Cl]o low and constant, the line relating the membrane potential with log [K]o has a slope of almost 50 mv. If [Cl]o is reduced in the absence of external Na, after the [K]o is increased to 45 mM, the membrane potential decreases with a slope of 59 mv per tenfold change in [Cl]o in close agreement with the Nernst equation. If Cl- is replaced by SO42-, a depolarization is produced, while chloride replacement by NO3-, Br-, and I- results in a hyperpolarization of the membrane. Removal of the external Na+ ions increases the average membrane potential by 17 mv.

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