[The role of fast and slow potassium currents in electrical activity of amphibian myelinated nerve fibres].

The paper reviews the information about the role of fast and slow potassium currents in electrical activity of amphibian myelinated nerve fibres. It demonstrates the importance of discovering of fast and slow potassium currents and their following pharmacological separation (by potassium channels blockers 4-aminopyridine and tetraethylammonium) in investigation of mechanisms of biological potentials generation. The information about the existence of fast and slow potassium channels in the nerve membrane and about the properties of 4-aminopyridine and tetraethylammonium action served as a base for determination the nature of biological potentials and discovering the mechanism of potential-dependent action of 4-aminopyridine that for tens of years suffered from the lack of adequate explanation.

[Prolonged after-potentials of the myelinated nervous fibres in amphibia after 4-aminopyridine-induced blockage of potassium channels].

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 potential area). These effects were time-dependent. The after-depolarization duration under 4-aminopyridine (4-AP) treatment changes in 3 phases: at the beginning of the exposure its duration 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 interchange of these phases accompanies by statistically significant increase of the action potential area (from 189.201 +/- 28.437 m x ms in normal solution to 489.945 +/- 41.75 m x ms 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.

[Transformation of electrical activity in the myelinated nerve fibres of amphibia by 4-aminopyridine].

Using the extracellular recording we studied the effect of 4-aminopyridine (4-AP), a potassium channel blocker on the electrical activity of the myelinated nerve fibres of amphibia Rana ridibunda Pallas. Two main types of the reaction on 4-AP were established: extension of the action potential and multi-spike response. In some cases the nerve fibres with multi-spike response generated spontaneous activity without stimulation in the form of bursts of action potentials. During repetitive stimulation 4-AP decreased after-depolarization (at the beginning of the stimulation), the posttetanic after-depolarization and the development of posttetanic after-hyperpolarization. Using the paired stimulation it was established that the spike and after-depolarization of the second action potential depended on the size of after-depolarization after the first action potential. The effects of 4-AP were strongly time-dependent.

[Postcatelectrotonic potentials and trace changes in the nerve fiber excitability]. / Postkatélektrotonicheskie potentsialy i sledovye izmeneniia vozbudimosti nervnykh volokon.

When cathode subthreshold impulse was turned off, excitable membranes of isolated nerve fibres and nervous trunk show postelectrotonic depolarisation (PED), that is a slow recovery of membrane potential to the resting level. PED of the single nodes of Ranvier and nervous trunk is registered not only in normal conditions, but also after complete block of sodium channels. The size and duration of nervous trunk PED under subthreshold depolarising current increase along with duration of applied depolarisation: when cathode current 1 ms in duration was used, they were 0.093 +/- +/- 0.004 mV and 7.123 +/- 0.576 ms, respectively; when current was 5 ms in duration, they were 0.189 +/- 0.005 mV and 23.212 +/- 1.186 ms, whereas a 10-ms depolarisation yields values of 0.220 +/- 0.011 mV and 68.721 +/- 3.389 ms. Application of the train of catelectrotonic impulses leads to PED built-up. As PED is found not only in normal conditions but also after complete block of sodium channels, it is reasonable to suggest that the most probable reason for PED is an outward potassium current.