E. Ujec

Work-induced potassium changes in skeletal muscle and effluent venous blood assessed by liquid ion-exchanger microelectrodes

SummaryUsing liquid ion-exchanger semimicroelectrodes with a side pore, we measured changes of extracellular potassium concentration (Ke+) in adult rabbit and cat gastrocnemius muscles and in venous effluent blood flowing from the cat gastrocnemius muscle during various bouts of activity induced by sciatic nerve stimulation.1.Isometric tetanic contractions (at 50 Hz) of various durations caused transient accumulation of Ke+ which was non-linearly related to the duration of muscle activity. The peak values of Ke+ in response to muscle stimulation were analogous in rabbits and cats, attaining values, e.g. after a 20-s isometric tetanus, between 8–9 mEq/lK+ in both species.2.Potassium concentration in venous effluent blood (Kven+) was transiently increased after isometric tetani. Since blood flow was measured at the same time, it was possible to calculate the amount of K+ lost by the muscle after tetani of various durations. A 32 g gastrocnemius muscle of the cat, for example, loses 9.36±1.52 μEqK+ after a 20-s isometric tetanus, which corresponds roughly to 0.5% of the total muscle potassium content. The loss of K+ in this muscle was 29.3 pEq K+/impulse/100 g fresh muscle tissue.3.There was no evident difference between the amount of K+ released during isometric tetani, or tetanic contractions performed under isotonic conditions. Single twitches evoked by indirect stimulation at 1 Hz for several minutes also induced a small rise in Kven+.4.If the loss of K+ from the muscle into the blood stream is transiently prevented by arterio-venous occlusion installed immediately before a 10-s isometric tetanus, most K+ is released subsequently when blood flow is renewed, if the occlusion lasts for 20–25 s. It is not until blood flow is occluded for 40–60 s that most K+ is apparently resorbed and only a minor portion is released and is to be found in the venous blood.5.The transient accumulation of muscle extracellular potassium may locally affect nerve endings, skeletal and smooth muscle cells.

The measurement of K e + concentration changes in human muscles during volitional contractions

Changes of extracellular potassium concentration ([K+]e) were measured in human muscles during volitional isometric contractions using liquid ion-exchanger electrodes. In principle, an intramuscular injection needle containing a microelectrode with a side-pore was inserted into the brachioradialis muscle. After insertion of the needle, the glass ion-selective microelectrode (ISM) could be moved out of the protective trocar shield into the muscle tissue. The average values of [K+]e in human muscles during maximal effort rose from 4.5 mmol/l K+ to 9.5 mmol/l K+. These values correspond closely to those previously found in muscles of experimental animals.

Low impedance coaxial K+ selective microelectrodes.

A procedure for preparing coaxial K+ selective microelectrodes with a low longitudinal resistance (Re) of the liquid ion exchanger selective barrel is described.The low resistance was attained by inserting another microelectrode filled with 0.5 mol·l−1 KCl into the ion-exchanger column (Corning 477317).The lower longitudinal resistance decreases the noise level and consequently increases the resolving power five times. This modification makes it possible to measure small and rapid K+ concentration changes.

Work-induced potassium changes in muscle venous effluent blood measured by ion-specific electrodes.

SummaryModified Walkers liquid ion-exchanger microelectrodes were employed for measuring changes of K+ concentration in venous effluent blood from the cat gastrocnemius muscle during and after isometric tetani of various duration induced by indirect stimulation. The time course of these changes was obtained and the overall loss of K+ from a working muscle could thus be estimated. By comparing present results in the venous blood and previous findings of K+ concentration changes in the muscle extracellular space, a concentration gradient was found between the muscle and venous effluent blood.

335 - Low-impedance, coaxial, ion-selective, double-barrel microelectrodes and their use in biological measurements

Abstract The transfer properties of the currently used double-barrel, ion-sensitive microelectrodes which are filled with liqui ion-exchangers may be substantially improved by decreasing the resistance of the ion-sensitive channel and by adjusting the geometry of the latter to that of the reference barrel. The dual purpose is achieved by using a thin micropipette as the reference barrel and by introducing a similar thin micropipette coaxially into the column of the ion-exchanger contained in the thicker ion-sensitive channel. The adjusted distance between the inner and outer tips results in decreased electrode resistance (to one tenth) and electrical time constant as well and noise reduction (to one fifth). It is demonstrated that such electrodes are suitable for recording fast and small changes in ion activities.

Response to stretch of proprioceptors in adult rat muscles de-efferented at brith

SummaryHind-limb muscles of new-born rats were de-efferented by removing the lumbosacral spinal cord. Spinal ganglia remained intact, together with their peripheral axon. The presence of sensory terminals in limb spindles, induces the full ultrastructural differentiation of muscle spindles, as has been shown previously. In the present paper we have shown by integrating the sensory discharges in the whole nerve from chronically de-efferented muscles that even several months after birth, muscle proprioceptors (probably mostly spindles) still maintain their basic mechanoreceptor properties. Although the limbs were completely immobilized throughout the whole experimental period, spindles from these chronically de-efferented muscles still responded as slowly adapting receptors. The dynamic component was also present in the integrated neurogram response during stretching. It thus appears that basic functional properties of rat muscle proprioceptors persist even when these receptors differentiate and survive without motor innervation and any adequate functional stimuli, i.e. under conditions of permanent disuse.

Double-Barrel Ion Selective [K+, Ca2+, Cl−] Coaxial Microelectrodes (ISCM) for Measurements of Small and Rapid Changes in Ion Activities

Double-barrel liquid ion-exchanger microelectrodes (ISM) are used at present to measure concentration changes in biological tissues (Lux et al., 1972; Vyklický et al., 1972; VyskoCil et al., 1972; Hnik et al., 1972; Lux and Neher, 1973; Oehme et al., 1976). The ISM (K+, Ca2+, Cl−) have a longitudinal resistance (Re) from 200 MΩ to 2 GΩ.

Potassium Changes Elicited in the Feline Somatosensory Cortex by a Single Stimulus to the Peripheral Nerve

In previous studies we measured changes in extracellular potassium concentration ([K+]e) elicited by repetitive stimulation in the cerebral cortex. Cortical K+ responses to single stimuli were buried in the noise to such a degree that they could not be differentiated for accurate measurements (Machek et al., 1975; 1976). This drawback of conventional double-barrel electrodes which were used in these studies was overcome by low-noise K+ selective, coaxial, double-barrel microelectrodes (ISCM) (Ujec et al., 1979; 1980 and in this volume) which make it possible to measure very small and rapid changes in K+ concentration.

Slow potential changes in experimental neocortical propagated foci

During and following interhemispheric stimulation (HS), characteristic negative slow potential changes (NSPCs) appeared which coincided with defined patterns of epileptic phasic field potentials (PFPs). Stimulus time-locked, high-amplitude, interhemispheric responses (IHRs), interictal and ictal patterns were accompanied by typical moderate NSPCs. In the wake of the latter, giant NSPCs occurred, concurrent with Van Harrevelds convulsions and/or either total or partial spreading, or local depressions. Partial depression of the PFPs and spreading of the moderate NSPCs were also present in the IHR stage. It is suggested that the moderate and giant NSPCs characterize two distinct types of experimental epileptogenesis which differ in the extent of alteration of the extracellular ion activities.

The Use of ISMs in Working Skeletal Muscles and Venous Effluent Blood

Even before the introduction of ion-selective microelectrodes (ISMs), it was known that K+ is released from contracting muscles. Loss of muscle K+ during contraction was described by Fenn (1936), and increased levels of K+ were subsequently demonstrated in the venous effluent blood by a number of authors (e.g. Kjellmer, 1965; Lind et al., 1966). Hinke (1959, 1961) was the first to employ ion-selective glass electrodes for measuring Na+ and K+ activities in muscle fibres. Since the tips of these electrodes were rather large, only giant muscle fibres could be impaled. Sorokina in 1964 succeeded in making microelectrodes selective for Na+ and K+ with tip diameters below 0.5 μm. It was not until 1972, however, that Gebert (1972) used K+ and Na+ ion-selective glass electrodes and our group (Hnik, Vyskocil, Křiž and Holas 1972) used the liquid ion-exchanger potassium ISMs to measure the time course and the extent of potassium accumulation in the contracting muscles and to assess potassium losses into venous effluent blood. In 1977, Hirche reported results on K+ changes and Friedman (1973) and Hirche (1977) have also measured pH changes in contracting muscles with microelectrodes.