Summary
Isolated protoplasmic droplets of the alga Nifella were investigated with microelectrodes under current clamp conditions. The following observations were made:
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1.
Long pulses of either polarity yielded almost symmetric current-voltage relations. Near the rather small resting potential (inside negative) the measuring points lay on a straight line corresponding to an apparent surface membrane resistance of 1.7±0.45 kΩ (mean ± S.E.M.,n=5).
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2.
Experiments with various pulse programs revealed no mechanism comparable to Na inactivation but stressed the electrical symmetry of the droplet with respect to the resting potential.
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3.
Changes of the [Ca2+] in the bathing medium between 0 and 10 mM as well as of the pH between 5 and 9 did not influence the responses. Replacing K+ by Na+ (or vice versa) or exchanging NO −3 for acetylglycine or Cl− was also ineffective.
These observations are not consistent with a normal excitable surface membrane. Similar responses are obtained with a RC network which is described and which may have its substrate in histological peculiarities of the protoplasmic droplet.
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Koppenhöfer, E. Electrical responses of isolated nitella protoplasm — Excitations or artifacts?. Pflugers Arch. 361, 263–267 (1976). https://doi.org/10.1007/BF00587291
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DOI: https://doi.org/10.1007/BF00587291