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THE DIRECT CURRENT RESISTANCE OF NITELLA
1Laboratories of The Rockefeller Institute for Medical Research.
The Journal of General Physiology
|October 30, 2009
Summary
The electrical resistance of Nitella cells was measured, revealing high protoplasmic resistance indicating low ion permeability. Potassium ions significantly reduce this resistance, suggesting high mobility.
Area of Science:
- Plant physiology
- Electrophysiology
- Cell membrane biophysics
Background:
- The electrical properties of plant cells are crucial for understanding their function.
- Nitella cells, with their large size, are ideal models for studying cellular electrical resistance.
Purpose of the Study:
- To determine the electrical resistance of Nitella cells to direct current.
- To calculate the effective protoplasmic resistance and its relationship with ion permeability.
- To investigate the effect of electrical stimulation on cell resistance.
Main Methods:
- Utilized a Wheatstone bridge with a vacuum-tube detector and string galvanometer for precise resistance measurements.
- Employed minimal currents to avoid stimulating the Nitella cells.
- Measured resistance with varying contact areas and solutions to differentiate between cell wall and protoplasmic resistance.
Main Results:
- Living Nitella cells exhibited high electrical resistance, typically 1,000,000–2,000,000 ohms, increasing to 3,500,000 ohms in optimal conditions.
- Protoplasmic resistance ranged from 100,000 to 700,000 ohms/cm², with a typical value of 250,000 ohms/cm².
- Resistance decreased significantly upon cell death (to ~50,000 ohms) and was markedly reduced by KCl solutions, but not by other salt solutions.
- Electrical stimulation led to a substantial resistance reduction, possibly due to KCl exomosis.
Conclusions:
- Nitella cell membranes possess high electrical resistance, implying low permeability to most ions.
- The high mobility of potassium ions (K+) in the protoplasm is indicated by the significant resistance decrease in KCl solutions.
- Electrical stimulation disrupts membrane integrity, leading to ion efflux and reduced resistance.
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