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The effect of internal and external 4‐aminopyridine on the potassium currents in intracellularly perfused squid giant axons
Author(s) -
Meves H.,
Pichon Y.
Publication year - 1977
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.1977.sp011869
Subject(s) - 4 aminopyridine , depolarization , chemistry , squid , pulse (music) , current (fluid) , potassium , biophysics , potassium channel , voltage , physics , biology , thermodynamics , fishery , organic chemistry , quantum mechanics
1. The effect of 4‐aminopyridine (4‐AP) on the K outward and inward currents in perfused giant axons of Loligo forbesi has been studied with the voltage‐clamp technique. 2. Small internal or external 4‐AP concentrations (10‐100 μ M ) considerably delay the rise of the K outward current. Repetitive pulsing with a pulse interval of 0·1‐5 sec leads to a faster rise of the K current; in 10 μ M 4‐AP a small effect is visible even with a pulse interval of 60 sec. 3. The phenomenon has been studied quantitatively by using a prepulse of varying height and duration, followed after 5 sec by a constant test pulse. The effect of changing the holding potential has been investigated. 4. The effect of repetitive pulsing disappears in higher 4‐AP concentrations; 1‐10 m M 4‐AP markedly reduce the size of the K outward current; the blocking effect is less pronounced for large depolarizing pulses than for small. 5. In K‐rich sea water 4‐AP reduces both the K outward current and the K inward current; the blocking effect on the K outward current is smaller than in K‐free sea water. 6. The K outward current in fibres treated with 10 μ M 4‐AP and immersed in K‐rich sea water is increased and accelerated by repetitive depolarizing pulses. The effect of repetitive pulsing is not dependent on the size of the K outward current (which can be increased by removing K inactivation). 7. The effect of repetitive pulsing and the voltage dependence of the 4‐AP block can be explained by the hypothesis that 4‐AP molecules are displaced from their blocking sites during the pulse and slowly rebound afterwards. Removal of the 4‐AP block by a depolarizing pulse seems to be a direct effect of the potential during the pulse and not related to K current.