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The effect of the tetraethylammonium ion on the delayed currents of frog skeletal muscle
Author(s) -
Stanfield P. R.
Publication year - 1970
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1970.sp009163
Subject(s) - tetraethylammonium , chemistry , depolarization , membrane potential , conductance , biophysics , iontophoresis , membrane , potassium , time constant , biochemistry , biology , neuroscience , mathematics , combinatorics , organic chemistry , engineering , electrical engineering
1. A method which permitted control of the membrane potential near the end of a muscle fibre and measurement of an approximation of the membrane current was used to investigate the effects of the tetraethylammonium (TEA) ion on the delayed outward potassium current obtained on depolarizing. 2. Assuming R i to be 250 Ω cm and a fibre diameter of 80 μ, the mean value for the maximum potassium conductance ( ḡ K ) was 23·2 ± 3·2 mmho.cm −2 . 3. 58 m M ‐TEA, in two series of experiments, reduced ḡ K by about 90%. A concentration—effect relation for TEA in its action on the delayed rectifier could be fitted by a curve for a drug‐receptor complex assuming one molecule of TEA to combine reversibly with one receptor, and a dissociation constant of 8 × 10 −3 M . 4. TEA tended to shift the threshold for delayed rectification to slightly more negative membrane potentials. TEA caused a similar shift in the relation between n ∞ and membrane potential, but did not much alter the form of the relation. 5. The relation between n ∞ and membrane potential and between τ n −1 and membrane potential were well fitted by the model of Adrian, Chandler & Hodgkin (1970 a ) assuming that the Q 10 was 2·5. 6. TEA slowed the rate of onset of the delayed potassium currents, decreasing τ n −1 (the reciprocal of the time constant of the fourth power function which described the current's development) by about 80%. 7. The inactivation of the delayed current with time was shown to follow a complex time course. A fast phase decays with a time constant of 270 msec and a slow phase with a time constant of 2·3 sec at a membrane potential of + 10 mV. 8. The fast phase of the delayed current is much more susceptible to the action of TEA than the slow phase, and these are interpreted in terms of different potassium channels. TEA has little effect on the time constant with which either the fast current or the slow current inactivates.