Work-induced potassium changes in skeletal muscle and effluent venous blood assessed by liquid ion-exchanger microelectrodes |
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| Authors: | Hník P Holas M Krekule I K?í? N Mejsnar J Smie?ko V Ujec E Vysko?il F |
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| Institution: | 1.Institute of Physiology, Czechoslovak Academy of Sciences, Budějovická 1083, 14220, Prague 4, Kr?, Czechoslovakia
;2.Department of Zoology, Charles University, 1200, Prague, Czechoslovakia
;3.Institute of Normal and Pathological Physiology, Slovak Academy of Sciences, Sienkiewiczova 1, 88423, Bratislava, Czechoslovakia
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| Abstract: | Using 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 (K
ven
+
) 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  EqK+ 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 K
ven
+
.
| | 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.
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