[Efferent potential-dependent ionic currents developing in frog myoblast culture].

Variety of outward voltage-dependent currents in cultured frog myoblasts were registered by means of whole cell voltage clamp. Six types of potassium currents (Ik) which reach the peak value (-10 mV) in 5, 12, 20, 30, 50 ms (fast) and do not reach the maximum in 7 s (slow) were established. High sensitivity to low temperature (+5 degrees) was shown for channels of very fast and of slow non-inactivated Ik.

[The potential-dependent incoming ionic currents of myoblasts from the frog Rana temporaria developing in culture].

Voltage-dependent inward ionic currents in 1-6-day cultured skeletal myoblasts have been studied using whole-cell patch clamp technique. Sodium (INa) and two types of calcium (ICa) currents were recorded at all stages. INa did not differ from that described in frog striated muscle fibres.

[The effect of N-bromoacetamide on the components of sodium channel inactivation in the membrane of Ranvier's node].

In voltage clamp experiments on the frog Ranvier node, the specific protein reagent, N-bromacetamide, significantly decelerates the sodium inactivation kinetics and makes it incomplete. After treatment with N-bromacetamide, both fast and slow inactivation time constants are increased and the proportion of inactivation components is changed favouring the slowly inactivating one in the wide range of membrane potentials. The results are consistent with a single channel population following the 3-state model of inactivation.

[Effect of niflumic acid on the components of inactivation of the sodium channels of the Ranvier node membrane].

In voltage clamp experiments on the frog Ranvier node, niflumic acid did not alter fast or slow inactivation time courses in the wide range of membrane potentials but reduced the amplitude of the fast phase of inactivation. Fast and slow currents, corresponding respectively to fast and slow phases of inactivation, reversed at the same voltage, revealed different activation- and inactivation-voltage dependences both in intact fibre and after application of niflumic acid. The latter induced a shift of the steady-state inactivation curves for both components of inactivation towards more negative potentials without changing their steepness.

[Analog-spike conversion in myelinated fibers. Role of potassium channels in digital coding].

Possible role of Ranvier node membrane fast and slow potassium channels in analog-to-digital transformation was studied. Rhythmic activity was computed in modified mathematical Dodge-Hill's model. Taking into account the slow channels contribution makes it possible to reproduce a special type of transformation in the model: numeric coding, whereas on account of varying the reversal potential for current through the slow channels, an optimal setting of the electrically excitable membrane to a certain range of stimulating current is possible.

[Kinetics of sodium current inactivation in Ranvier's node membrane].

The possibility to describe the inactivation kinetics of sodium current in the Ranvier node membrane in terms of models with independent processes of activation and inactivation, was experimentally tested. Dependence of kinetic characteristics on the potential suggested the existence of three types of nerve fibers with different models of inactivation system. The models with independent systems of activation and inactivation were concluded to be not quite adequate.

[Kinetic model of the gating system of the sodium channel in a Ranvier node membrane].

A kinetic model of the sodium channel gating system consisting of four subunits with three states--closed (X), open (Y) and inactivated (Z)--is proposed. For the channel to conduct, all the four subunits must be in the open state. The transitions between states X and Y are independent, while those between states X and Z are coupled, so that for the particle considered transition of one of two neighbouring particles into state Z increases the activation energy of the step by kT.

The Cole-Moore effect in nodal membrane of the frog Rana ridibunda: evidence for fast and slow potassium channels.

The K conductance (gK) kinetics were studied in voltage-clamped frog nodes (Rana ridibunda) in double-pulse experiments. The Cole-Moore translation for gK--t curves associated with different initial potentials (E) was only observed with a small percentage of fibers. The absence of the translation was found to be caused by the involvement of an additional, slow, gK component.

[2-component nature of the displacement currents in a nerve fiber membrane: a kinetic and pharmacological analysis].

Asymmetrical displacement currents in the Ranvier node membrane were recorded in the normal Ringer and under the action of a neurotoxin from the scorpion Buthus eupeus venom and of the alcaloid aconitine. In the total displacement current (DC) at the beginning of the pulse (Ion), two-exponentially decaying components were extracted: a rapid component with the maximum time constant of decay about 70 microns, and a slower one with the time constant of decay--300 microns. At high negative levels of conditioning prepulse (Vc) (-130 divided by -145 mV), the maximum value of the charge transferred by the fast and slow components was estimated to be 2.

[Effect of aconitine on asymmetric displacement currents in the membrane of a node of Ranvier].

The effect of aconitine on the asymmetrical displacement currents in Ranvier node membrane was studied. Aconitine evokes a shift of the charge displacement and time constant (tauon) membrane potential plots for the displacement currents in the direction of hyperpolarization by 50 mV. Maximum value of tauon in aconitine is twice as high as in norm and the reversal potentials for the displacement currents was estimated to be about--90 mV.

[Displacement currents of the sodium channels of the membranes of Ranvier's nodes].

A method to record the displacement current in nodal membrane is described and results obtained on nerve fibres from the frog Rana ridibunda are presented. This current is shown to be due to displacement of charges from an initial state, associated with a large negative membrane potential, to a final state. The dependence of the charge displacement on the membrane potential and degree of inactivation of the sodium channels suggests that the displacement current observed in these experiments is associated with activation of m-gates of the sodium channels.