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Prolonged after-potentialsof myelinated nervous fibres ofamphibian after blockage of potas-sium channels by 4-aminopyridine
I.V. Kuznetzova, D.A. Evstigneev, N.V. Gluhova.
Ecological Foundation, Ulianov Region, Russia
Abstract
Myelinated nerve fibres of Rana ridibunda Pallas were studied
by using extra-cellular recording technique. 4-aminopyridine,
a blocker of fast potassium channels produced considerable
changes in duration of the after-depolarization and increase in
total membrane depolarization (evaluated by an action poten-
tial area). These effects were time-dependent. The after-depo-
larization duration under 4-aminopyridine (4-AP) treatment
changes in 3 phases: at the beginning of the exposure its dura-
tion increased; then the increase stopped; and later duration of
the after-depolarization start to decrease. The last phase was
often followed by hyperpolarizing after-potential. The inter-
change of these phases accompanies by statistically signifi-
cant increase of the action potential area (from 189.201 ±
28.437 mVЧms in normal solution to 489.945 ± 41.75 mVЧms
in 5 minutes after 4-AP application). These observations are
explained as a result of the increased activation of the slow
potassium channels and decreased portion of fast potassium
channels involved in membrane repolarization. The decrease
in post-tetanic depolarization duration, the appearance of the
post-tetanic hyperpolarization at low frequencies and increase
of post-tetanic hyperpolarization at higher frequencies of
stimulation under 4-AP treatment are dependent on activation
of slow potassium channels.
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© National Academy of Sciences of Ukraine, Bogomoletz Institute of Physiology, 2014-2024.
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