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Evoked electrical and mechanical activities of pregnant human myometrium were recorded by the single sucrose-gap method. Each muscle strip has an individual rhythm of membrane excitability and the evoked activity was affected by spontaneous membrane fluctuation. However, high-frequency stimulation caused changes in the rhythm of fluctuation and the pattern of action potential converted from plateau to spike type. Twitch contractions evoked by spike potentials were summated and became fused tetanus in accordance with shortening of the pulse interval. This method is suitable for clarifying the excitation contraction relationship in human myometrium.

Der Wirkungsmechanismus von „muskulotropen“ Relaxantien der glatten Muskulatur ist bisher nicht genugend physiologisch definiert. Es ist daher von Interesse, das Iproveratril (Isoptin) und sein nachster Verwandter D 600 [1] (α-Isopropyl-α-[(N-methyl-N-homoveratryl)-γ-aminopropyl]-3, 4, 5-trimethoxyphenylacetonitril) sowie Prenylamin (Segontin) am isolierten Uterus von virginellen Ratten in Tyrodelosung eine 10–30mal starkere muskulotrop-relaxierende Wirkung als Papaverin besitzen. Die genannten Stoffe blockieren dabei die elektromechanische Koppelung in den glatten Muskelzellen spezifisch durch einen Ca++ -antagonistischen Effekt; sie heben infolgedessen schon in einem Konzentrationsbereich von etwa 5 ° 10−6 M/l die Contractilitat der glatten Muskelzellen so weitgehend auf, das sie bei Depolarisation durch isotonische KCl-Losung, kathodische Gleichstromapplikation, Acetylcholin, Carbaminoylcholin, Oxytocin und Bariumchlorid kaum mehr mit einer Verkurzung reagieren. Bei Reduktion des Ca++ -Gehalts der Tyrodelosung auf ein Viertel (0, 45 mM/l) der Norm (1, 8 mM/l) werden die Effekte der Ca++ -Antagonisten betrachtlich verstarkt. Umgekehrt wird die Ansprechbarkeit der Uterus-Muskulatur auf die genannten Kontrakturstoffe bzw. auf kathodische Gleichstrom-Polarisation wieder hergestellt, sobald man in die Iproveratril, D 600 oder Prenylamin enthaltende Tyrodelosung CaCl2 im Uberschus zusetzt und dadurch die elektro-mechanische Koppelungsfunktion restituiert.

THE problem of the excitation-contraction link in muscle cells has long been one of the chief fields of modern muscle physiology1–4. Of many reports in this field, one of the most interesting was the demonstration of the inhibition of the linking function due to the osmotically hypertonic condition, as demonstrated by Hodgkin and Horowicz3. Though this demonstration is striking, it does not help to analyse the linking system, since the condition used is rather unspecific. It seems to be of importance to search for substances which may remove the inhibitory effect of the hypertonic condition. This communication deals with the problem and demonstrates that the potassium ion has the aforementioned removing effect.

Dantrolene sodium, a skeletal muscle relaxant, inhibits the twitch response by direct action on the muscle. The action potentials from dantrolene sodium depressed muscles have been examined by taking their first derivative, and membrane capacitance has been measured with cable analysis techniques. It is concluded that dantrolene sodium has no effect on the electrical excitability of the muscle and uncouples excitation-contraction mechanisms.

The authors consider the use of the evoked EMG (EEMG) signal that is obtained using surface electrodes, to track changes in the torque generated at the knee when the vastus-lateralis muscle in paraplegic subjects is stimulated via percutaneous intramuscular electrodes. This was done under isometric conditions, during six minutes of sustained stimulation at constant amplitude, pulse width and pulse frequency. The authors show that there are three states in muscle behavior during prolonged stimulation potentiation, fatigue and maximal fatigue. These three states can be characterized from time-domain and frequency-domain parameters of the EEMG signal. It was observed that the amplitude of the EEMG increases during potentiation, decreases during fatigue, and begins to increase during maximal fatigue. During maximal fatigue, the firing rate of motor unit action potentials decreases. In all three states, there is a high correlation between the generated torque and the EEMG.

In the rat hemidiaphragm, in vitro dantrolene sodium irreversibly reduced twitch tension up to 20% of the original value in 20 minutes of exposure. The phenomenon was dose related. Dantrolene sodium did not affect (1) resting membrane potential (IMP); (2) miniature endplate potential frequency of amplitude; or (3) endplate potential amplitude decrement of repetitively stimulated partially curarized muscle. A combination of hyperosmolar solutions of glycerol and dantrolene sodium abolished contraction of mammalian muscle with no demonstrable effect on neuromuscular transmission or muscle fiber RMP. With this technique, prolonged recording from repetitively activated muscle fibers is possible.