Reliability of ionic current measurements in Ranvier nodes.

A mathematical formalism was developed comprising four performance parameters to analyse electronic feedback systems for voltage clamp measurements in myelinated nerve fibres. The effects of the so-called Schmidt-Lanterman incisures and of the nodal series resistance were of particular interest here. Starting from passive standard data from myelinated nerve fibres, we calculated the frequency dependence of the above mentioned parameters for the measuring systems according to Nonner, to Dodge and Frankenhaeuser, and to Bohuslavizki and coworkers. It turned out that the latter system is clearly preferable to the two remaining systems for ionic current measurements in Ranvier nodes.

Electrical noise of axon membrane and its behaviour as an adaptive system.

Spectral analysis of stimuli in the excitation processes has revealed interesting correlations between macroscopical events (reflected in the excitation threshold of the nerve membrane) and microscopical events (reflected in electrical noise associated to the ionic currents) accompanying the generation of the nerve impulse. According to our analysis, the threshold function of nerve excitable membrane can be modelled by satisfying; (a) the energetic condition at low frequency and (b) the condition of spectral covering. One of the most important predictions of this model concerns the behaviour of axon membrane only in hyperpolarization as filters adapted to signals commonly used as physiological stimuli (rectangular, sinusoidal, or ramp stimuli). This prediction has generated two new theoretical objectives formulated as follows: What is the functional model of a filter adapted to a signal having the shape of an action potential; what is the signal adapted to a filter with a frequency characteristic similar to that obtained when applying white noise to the membrane biased near the excitation threshold. Our most recent studies performed by computer simulation allowed us to approach these problems.

Problems concerning the measurements of electrical events in myelinated nerve fibers.

As only the availability of strictly accurate data enables the realistic theoretical modelling of the ionic channel behaviour, the most important and topical problems concerning the measurements of the electrical events at the level of the myelinated nerve fiber are analysed. Thus, the following aspects are examined: (a) morphological characteristics of the myelinated nerve fiber and problems arising from the membrane currents measurements: (b) problems induced by use of the insulating layers on the myelin surface: air gap or vaseline seal insulation; (c) effect of the nodal gap resistance on the ionic currents measurements in the node of Ranvier membrane.

The structure-function relationships in the ionic channels of the axonal membranes as revealed by deuteration.

The present study has two purposes: c) to summarize our most important experimental results concerning the deuteration effects on the Ranvier node membrane as well as those obtained by others on the giant axons; ii) to reveal the significance of the macroscopic-microscopic correlations reflected in the excitation processes which underlie the ionic channel behaviour and for which deuteration has provided a new alternative of investigating the molecular mechanisms.

Abolishment of the Ranvier node excitability under quasi-total deuteration and rhythmic stimulation.

The isolated nerve fibre, when quasi-totally deuterated, loses its excitability after about 15' of rhythmic stimulation at frequencies of 150-200 Hz. It is only on internal rehydration that excitability is recovered at high frequencies of stimulation. An excitation-energy coupling is suggested to exist, which appears to be more obvious at high frequencies of stimulation and strongly affected by the proton-deuteron exchange in the intracellular medium.

Computer simulation of the effect of the nodal gap resistance on ionic current measurements in the Ranvier node membrane.

Results are presented of a computer simulation of the effect of the irreducible resistance introduced by the nodal gap, in series with the impedance of the axon membrane. A clamp potential is applied to a structure modeled as an electric circuit composed of a resistance in series with the membrane impedance, and modified nerve equations describing membrane currents are solved to predict the effect of nodal series resistance on these currents. These studies reveal changes in the absolute values and kinetics of the ionic currents (errors greater than 10-20%) for selected values of series resistance.

2H2O effects on ATP pool in frog stimulated nerve.

On stimulation a decrease of ATP pool was observed in the nerve immersed in 2H2O as compared to that of the nerve in H2O. Among the phenomena possible to account for this decrease, we are tempted to attach weight to the transfer rate of protons which finds expression in an increased raising time of the action potential, a stage in which the energy system is stressed.

Contributions to the perfecting of the enzymatic method used for the determination of ATP in biological systems.

The improvement of methods for the determination of ATP, that is the increasing of their sensitivity is extremely useful for the study of excitation-energy coupling in excitable membranes. Such investigations from the object of the present work in which there is proved that the microanalytical method for the dosing of ATP, based on the enzymatic reaction with luciferin-luciferase system, may be converted into a ultramicroanalytical method and therefore used also in other fields of research, as for example the ATP biosynthesis in cell cultures.