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

Using liquid ion-exchanger semimicroelectrodes with a side pore, we measured changes of extracellular potassium concentration (K_e ⁺) 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.

Slow potential changes in experimental neocortical propagated foci

During and following interhemispheric stimulation (IHS), 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 occured, 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.     

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

Summary Modified Walker's 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.The authors wish to acknowledge the assistance of Dr. J. L. Walker in developing the ion-specific microelectrodes and for supplying them with silicone oil and Corning ion-exchanger.     

Changes of extracellular potassium concentration induced by neuronal activity in the sinal cord of the cat

1. Changes of extracellular K(+) concentration, [K](e), arising in the spinal cord of the cat in response to an afferent stimulation were studied by means of K(+)-specific micro-electrodes.2. In the most active areas of the spinal cord a single volley in a large afferent input like the common peroneal nerve or the posterior tibial nerve produced a transient increase in [K](e) of 0.05-0.1 mM, which reached its peak in 0.2-0.3 sec and it declined in about 3 sec.3. Much higher increases in [K](e) were found during repetitive stimulation of an afferent input. The highest increase (by 3 mM) was at 100 Hz, but even at 1 Hz a significant increase of 0.25 mM was observed. Equilibration of accumulated K(+) was slow with a time constant of about 6 sec, which is much longer than could be expected for the same process in free solution.4. A characteristic distribution of increased [K](e) was found in the spinal cord in response to 100 Hz afferent stimulation. The highest increase of 3 mM was found in and around the intermediate nucleus, but at depths between 0.9-1.8 mm the [K](e) increase exceeded 1 mM.5. In the ventral horns afferent stimulation (100 Hz) increased [K](e) by 0.25 mM, while the same stimulation of the ventral root resulted in a [K](e) increase of less than 0.05 mM.6. The consequences of K(e) (+) accumulation after neuronal discharge are discussed in respect to its possible role in the depolarization of primary afferent terminals.     

Projection of tooth pulp afferents to the brainstem and to the cortex in the cat

The projection of tooth pulp afferents in the spinal trigeminal nucleus (N.V.sp.) and the effect of dorsolateral medullotomy on cortical potentials evoked by electrical stimulation of Adelta tooth pulp nerve fibres were studied in cats. It was confirmed that antidromic responses were recorded in the tooth pulp nerve to stimulation of the ipsilateral but not the contralateral N.V.sp.[11]. Dorsolateral medullotomy at the level of the obex did not alter the cortical potentials induced by single pulses applied to the tooth pulp. It is concluded that Adelta tooth pulp afferents project exclusively to the ipsilateral trigeminal nucleus and that the impulse transmission to the cortex persists after transection of the pars caudalis of the N.V.sp.     

Evidence that excitatory amino acids not only activate the receptor channel complex but also lead to use-dependent block

The effects of fast application of excitatory amino acids N-methyl-D-aspartate (NMDA), L-aspartate (ASP), L-glutamate (GLU), quisqualate (QU) and kainate (KAIN) were studied in neurons from the embryonic spinal cord of the chick in monolayer cultures by employing the 'patch clamp' technique in the 'whole cell' mode. It was found that NMDA, ASP, GLU and QU, but not KAIN, induced responses that exhibited several components. The early component decayed with a time constant of 2 s to a lower level of membrane current and discontinuation of the application was followed by an after-current which returned to the base-line with a time constant of about 7 s. It is suggested that NMDA, ASP, GLU and QU, but not KAIN, not only activate the receptor channel complex but also induce use-dependent block.