In vitro human masseter muscle hypersensitivity: a possible explanation for increase in masseter tone.

To determine whether a difference in fiber-type caffeine and Ca2+ sensitivities exists between human masseter and vastus lateralis skeletal muscle, we compared the fiber-type caffeine sensitivities in chemically skinned muscle fibers from 13 masseter and 18 vastus lateralis muscles. Caffeine sensitivity was defined as the threshold concentration inducing > 10% of the maximal tension obtained after the fiber was loaded with a 1.6 x 10(-2) mM Ca2+ solution for 30 s. Significant difference in the mean caffeine sensitivity was found between type I masseter fibers [2.57 +/- 1.32 (SD) mM] vs. type I (6.02 +/- 1.74 mM) and type II vastus lateralis fibers (11.25 +/- 3.13 mM). Maximal Ca(2+)-activated force per cross-sectional area was significantly different between masseter and vastus lateralis fibers. However, the Ca2+ concentration corresponding to half-maximal tension (pCa50) was not significantly different between type I masseter (pCa50 5.9 +/- 0.02) and type I vastus lateralis muscle (pCa50 6.01 +/- 0.08). These results suggest that the increase in caffeine sensitivity of masseter muscle reflects the presence of a low reactivity threshold of the sarcoplasmic reticulum.

Shortening velocity of skeletal muscle from humans with malignant hyperthermia susceptibility: effects of halothane.

The aim of this investigation was to assess the effect of halothane on the velocity of shortening and lengthening of muscle from normal subjects and from patients with malignant hyperthermia susceptibility. Strips were mounted horizontally at optimal length in normal Krebs-Ringer's solution and mechanical parameters were obtained before and after exposure to 3 vol.% halothane. The maximun shortening velocity at zero load (V(max)) was determined by using Hill's characteristic equation. The contraction and relaxation indices were measured under isotonic and isometric conditions: maximum shortening and lengthening velocities (maxV(c) and maxV(r), respectively); isometric peak twitch tension; peak of the positive (+dP/dt(max)) and negative (-dP/dt(max)) twitch tension derivative; ratio R1=maxV(c)/maxV(r) and ratio R2=(+dP/dt(max))/(-dP/dt(max)). In normal muscle, halothane markedly increased V(max), maxV(c) and peak twitch tension by 30+/-10%, 30+/-5% and 40+/-15%, respectively. The maxV(r) values increased concomitantly with the maxV(c) values, such that no change in the ratio R1 was observed. Both +dP/dt(max) and -dP/dt(max) increased such that the ratio R2 did not vary. In malignant hyperthermia susceptibility muscle, halothane induced a significant decrease in V(max) (-30+/-10%) and maxV(r) (-45+/-15%) without changing maxV(c). The decrease in maxV(r) was greater than that of maxV(c), such that the ratio R1 increased significantly. Peak twitch tension and +dP/dt(max) remained unchanged whereas -dP/dt(max) decreased significantly; the ratio R2 increased by 40+/-10%. These results suggest that halothane alters the contractile properties of malignant hyperthermia susceptibility muscle.

Effects of halothane on mechanical response of skeletal muscle from malignant hyperthermia susceptible patients.

The purpose of this investigation was to compare the effects of halothane on malignant hyperthermia (MH) and normal isolated muscle bundle performance during isometric contraction and relaxation phases. Mechanical parameters were measured: peak tension (PT), time to peak tension (TPT) and positive peak of isometric tension derivative (+dP/dtmax) characterized the contraction phase. Half-relaxation time (RT1/2) and negative peak of isometric tension derivative (-dP/dtmax) characterized the relaxation phase. The ratio R = (+dP/dtmax)/(-dP/dtmax) was used to study the coupling between contraction and relaxation under isometric condition. In normal muscle, halothane increased PT by nearly 40% without altering TPT. The +dP/dtmax value increased concomitantly with the -dP/dtmax values, thus no changes in R was observed. In MH muscle, PT was first potentiated (0.5-1.0 vol% halothane) and then depressed (2.0-3.0 vol% halothane). TPT and +dP/dtmax were not altered whereas RT1/2 increased progressively with concomitant decrease in -dP/dtmax, thus R increased by nearly 40%. The amplitude of MH muscle contracture with stepwise concentrations of halothane was correlated with the increase of RT1/2 and R, and the decrease of -dP/dtmax. These results suggest that halothane alters the relaxation phase more than the contraction phase in MH human skeletal muscle compared to normal muscle.

[Caffeine skinned fiber tension test: application to the diagnosis of susceptibility to malignant hyperthermia]. / Test à la caféine sur fibres pelées: application au diagnostic de la susceptibilité à l'hyperthermie maligne.

OBJECTIVE: To assess the reactivity of sarcoplasmic reticulum to caffeine, using the skinned muscle fibre tension test and to compare it with the reference in vitro contracture test in the diagnosis of malignant hyperthermia (HM) susceptibility. STUDY DESIGN: Laboratory investigation. MATERIAL: Muscle biopsies from 63 patients, including 29 classified as susceptible to MH (MHS) and 34 classified as non-susceptible (MHN) according to criteria of the European and the North American MH groups. METHOD: The reactivity to caffeine and halothane of skinned muscle fibres was compared, according to the type of fibres, with the data of the in vitro contracture test. The type of fibres (type I: oxidative, slow; type II: glycolytic, fast) were determined with strontium dose-response curves. RESULTS: The reactivity to caffeine was significantly lower in the MHS group, for both type I and type II skinned fibres. However, in comparison with the data of the in vitro contracture tests, using the ROC curve analysis, the best sensitivity-specificity compromise was 90%-71% and 74%-84% for type I and type II skinned fibres respectively. CONCLUSION: The skinned muscle fibre tension test cannot be used instead of the in vitro contracture test for the diagnostic of MHS. However, it may strengthen the data of the latter.

[Contraction-relaxation coupling of skeletal muscle in patients susceptible to malignant hyperthermia]. / Etude du couplage contraction-relaxation du muscle squelettique de patients susceptibles à l'hyperthermie maligne.

OBJECTIVE: To assess whether halothane exposure could influence contraction-relaxation coupling of human skeletal muscle with malignant hyperthermia susceptibility. STUDY DESIGNED: Laboratory investigation. MATERIAL AND METHODS: Muscle biopsies from 14 patients, including six classified as susceptible to MH (MHS) and eight as classified as non-susceptible (MHN) according to criteria of the European MH group. Mechanical parameters of strips were obtained before and after 3 vol% halothane exposure. The contraction and relaxation parameters were measured under isotonic and isometric conditions: maximum shortening and lengthening velocities (respectively maxVc and maxVr); peak of the positive (+dP/dtmax) and negative (-dP/dtmax) twitch tension derivative; ratio R1 = maxVc/maxVr and ratio R2 = (+dP/dtmax) (-dp/dtmax). RESULTS: In MHN muscle, halothane markedly increased maxVc and maxVr, so that the ratio R1 was unchanged. Both +dP/dtmax and -dP/dtmax increased such that the ratio R2 did not vary. In MHS muscle, halothane induced a significant decrease in maxVr (p < 0.05) without changes in maxVc, so that the ratio R1 increased significantly. +dP/dtmax remained unchanged whereas -dP/dtmax decreased significantly; the ratio R2 increased (p < 0.05). CONCLUSION: Our results indicated that, in MHN muscle the contractility property is improved with halothane exposure. In MHS muscle, halothane caused an impairment of relaxation. The mechanical abnormalities observed in this study might be related to sarcoplasmic reticulum dysfunction in MH diseases.

[Inward currents of crab striated muscle fiber measured by the voltage clamp technique with microelectrodes]. / Le courant entrant de la fibre musculaire striée de crabe mis en évidence par la technique du potentiel imposé avec micro-électrodes

Membrane currents during depolarisation steps were determined by a method in which three electrodes were inserted near the end of the crab's striated muscular fibre. The value of the reversal potential for the early current appears to be consistent with the calcium equilibrium potential. This early transient inward current is abolished by manganese. The value of about +120mV is consistent with the level of internal free Ca++ ions, as generally tested by different authors.

[The effect of tetraethylammonium and the decrease in the extracellular chloride concentration on membrane depolarization and contraction of skeletal muscle fiber induced by a hyperpotassium solution]. / Influence du tétraéthylammonium et de la diminution de la concentration extracellulaire en chlore sur la dépolarisation membranaire et la contracture de la fibre squelettique induites par un milieu hyperpotassique.

1.--The tetraethylammonium (TEA) effects on K+ contracture and membrane depolarization are compared in both crab and frog skeletal muscle fibres. 2.--The mechanical tension of the contracture is reduced by the TEA in frog skeletal muscle fibre; it is increased in crab skeletal fibre. 3.--When no mechanical phenomenon is observed in frog skeletal muscle, the amplitude and the velocity of membrane depolarization induced by an increase of outward K+ concentration is reduced by the TEA. These effects are in opposition in crab muscle fibre. 4.--In crab muscle fibre, the results obtained tend to show that the C1-ions are not distributed on each side of the membrane according to Donnan equilibrium.

[Modification of the affinity of actomyosin calcium sites by anions]. / Modification de l'affinité des sites calciques de l'actomyosine par les anions.

ATP hydrolysis-pCa and isometric tension-pCa relationships were determined for isolated myofibrils under a variety of ionic conditions i.e. in presence of Cl- ions (normal conditions), in presence of CH3COO- or CH3OSO3- (ions replacing all or a part of Cl- ions). In all ionic conditions, these relationships have a S-shape. For each ionic condition, the relationships between isometric tension or ATP hydrolysis and pCa were parallel, but the isometric tension-pCa was shifted towards a smaller value of pCa. The relation between ATP hydrolysis and pCa has been analysed by means of the enzymatic reaction described by Michaelis-Menten. The analysis of isometric tension-pCa relationship can be also described by using the consecutive scheme of reaction for the co-operative action of two Ca2+ ions in the process of tension activation given by Ashley & Moisescu (1977) for barnacle myofibrils. The dissociation constant (k1) equal to the one that we determined for the ATP hydrolysis probably corresponds to the Ca2+ binding site of troponin (M1). This association (M1-Ca) would lead to the phosphorylation of the second site (M2) localized on myosin, which can bind a Ca2+ ion. In presence of CH3COO-, ATP hydrolysis (V) was increased with no change of the affinity of the first site for the Ca2+ ion. At the opposite, V did not change but the affinity of M1 site was decreased in presence of CH3OSO3-. CH3OSO3- must be considered as a competitive inhibitor whereas CH3COO- must be considered as an activator ion of the ATP hydrolysis reaction. In all cases, the relationship between isometric tension and ATP hydrolysis was hyperbolic.

[Inhibition, by an amphiphilic substance, niflumic acid, of the inward rectification of the crustacean muscle fiber]. / Inhibition par une substance amphiphile, l'acide niflumique, de la rectification dans le sens entrant de la fibre musculaire de Crustacé.

Agents such as TEA+ or CS+ ions, these last ions instead of K+ ions in poor K extracellular solution, known to reduce or abolish the inwardly rectifying channel in many preparations produced no effect in crayfish muscle membrane By contrast, poor Cl extracellular solution (Cl- ions were replaced by CH3OSO3- ions) blocked the inward current activated by hyperpolarizing pulses and produced an increase of the resting potential. Niflumic acid is a agent which inhibited the inward going rectification of the crayfish muscle membrane. Apparent dissociation constant of niflumic acid with membrane sites was equal to about 6 X 10(-8) M; this value corresponds to that given by Cousin & Motais (1979) concerning translocation of Cl- ions in the membrane of red cells. Activation of the inward going rectification in the crayfish membrane is responsible of an inward current carried by Cl- ions.

[Effects of hypertonic solutions on the excitation-contraction coupling of the skeletal muscle fibre of the crab. II. Ultrastructural aspects (author's transl)]. / Effets de l'hypertonie sur le couplage excitation-contraction de la fibre musculaire squelettique de crabe. II. Aspects ultrastructuraux.

Experiments were performed to investigate the modifications of electrical activity and the loss of contraction by examination of the ultrastructure. These alterations were obtained with a control physiological solution (artificial sea water, ASW) which was made hypertonic by adding sucrose, glycerol, choline chloride or urea. 1. Under these conditions, the ultrastructural results show that: a) all those substances induce a modification of the coupling junction (either diad or triad). This modification can explain the inhibition of the mechanical phenomenon; b) sucrose (Figs. 6C and 6D) and glycerol (Figs. 4A and 4B) induce alterations of the surface membrane and of the tubular system (less important with glycerol). They can explain the decrease of the resting potential and the abolishment or the modification of the action potential; c) in contrast, choline chloride (Figs. 7A to 7E) and urea (Figs. 9A to 9F) only modify the organisation of the coupling junction. The action potential is maintained. 2. A short exposure of the fibre in an isotonic sucrose solution (Figs. 5A to 5D) deeply modifies the tubular system, particularly, in cutting it off from the sarcolemma. 3. Choline chloride and urea produce similar changes in the ultrastructure but as urea is not ionized, it can be added to the ASW to investigate the electrical phenomenon which cannot be modified by contraction.

Effects of calcium-free solution, calcium antagonists, and the calcium agonist BAY K 8644 on mechanical responses of skeletal muscle from patients susceptible to malignant hyperthermia.

The purpose of this investigation was to determine if alteration in the function of the dihydropyridine receptor may in turn modify halothane-induced contractures in muscle bundles from patients susceptible to malignant hyperthermia (MH). The effects of Ca(2+)-free Krebs Ringer (KR) solution, 5 microM verapamil, 5 microM nifedipine, and 10 microM of the Ca2+ agonist BAY K 8644 on halothane-induced contracture were therefore investigated. The halothane-induced contracture was prevented in the absence of extracellular Ca2+ and significantly reduced in the presence of verapamil or nifedipine. BAY K 8644 significantly enhanced the 0.5-, 1.0-, and 1.5-vol % halothane-induced contracture in MH-susceptible muscle bundles. When BAY K 8644 was dissolved in Ca(2+)-free KR solution, no contracture was observed in MH-susceptible muscle bundles. These results on cut MH-susceptible human muscle bundles support the hypothesis that halothane-induced contracture in MH can be modified by the binding of Ca2+ agonists or antagonists to the dihydropyridine receptor. The role of Ca2+ entry phenomena remains unclear, but the results suggest that extracellular Ca2+ is required to reprime or to bind to some sites of the dihydropyridine receptors.

Effect of Bay K 8644 on the magnitude of isoflurane and halothane contracture of skeletal muscle from patients susceptible to malignant hyperthermia.

Isoflurane has a lesser ability than halothane to induce contracture in malignant hyperthermia (MH) muscle in vitro. This does not necessarily imply that isoflurane is not as potent an MH trigger as halothane in vivo. A hypothesis was tested that in vitro treatment with Bay K 8644, an activator of both the dihydropyridine receptors as well as the sodium channels of the T-tubules, potentiates isoflurane-induced MH-susceptible skeletal muscle contracture. In addition to the usual halothane-caffeine test, other muscle bundles were exposed to 10 microM Bay K 8644-halothane and equipotent anesthetic concentrations (expressed in multiple minimum alveolar concentration [MAC]) of isoflurane either alone or combined with Bay K 8644. In 14 MH-susceptible muscle bundles, the mean maximum contracture induced by 2 MAC isoflurane was 0.20 +/- 0.22 g (mean +/- SD), and this value was significantly less than that obtained with 2 MAC halothane (0.68 +/- 0.40 g). Bay K 8644 did not induce muscle contracture on its own but consistently enhanced both the 0.5 MAC isoflurane and halothane to the same maximal isometric tension (1.09 +/- 0.35 g and 1.11 +/- 0.37 g, respectively). Such an effect was not observed in the MH-nonsusceptible group. Under the conditions of this in vitro study, 0.5 MAC isoflurane appears to be as potent as halothane in inducing muscle contracture in skeletal muscle bundles from individuals susceptible to MH.

Is resting membrane potential a possible indicator of viability of muscle bundles used in the in vitro caffeine contracture test?

In 22 patients susceptible to and 34 patients not susceptible to malignant hyperthermia, we examined which muscle conditions may influence the degree of sensitivity of skeletal muscle to the in vitro caffeine contracture test: predrug resting membrane potential, predrug twitch tension, and maximum contracture induced by 32 mM caffeine in two caffeine tests performed respectively at 30 and 75 min after biopsy. No differences in the measured variables were observed between the first and the second caffeine tests in the 34 patients susceptible to malignant hyperthermia. The first caffeine test was found to be positive in all of the 22 patients susceptible to malignant hyperthermia. However, in eight patients, the second caffeine test was negative and the muscle fibers were found to be significantly depolarized. Resting membrane potential was -73.4 +/- 7.9 mV before the first caffeine test and -65.8 +/- 8.8 mV before the second test. We suggest that when time-induced partial depolarization of malignant hyperthermia-susceptible fibers occurs, fibers may become less sensitive to caffeine.

Effects of veratridine on mechanical responses of human malignant hyperthermic muscle fibers.

BACKGROUND: To determine if alteration in the function of the sodium channel may in turn modify halothane-induced changes in mechanical responses of muscle bundles from patients susceptible to malignant hyperthermia (MH). METHODS: Mechanical responses of muscle bundles from 12 MH-susceptible and 20 MH non-susceptible patients were measured prior to and during administration of halothane alone and in the presence of 10 microM veratridine, an inhibitor of sodium channel inactivation. Peak tension (PT), time to peak tension (TPT), positive peak of isometric tension derivative (+dP/dtmax) were used to characterize the inotropic state. Analysis of relaxation process was performed using half relaxation time (RT 1/2) and the negative peak of isometric tension derivative (-dP/dtmax). The ratio (R) = (+dP/dtmax)/(-dP/dtmax) was used to measure the coupling between contraction and relaxation under isometric condition. RESULTS: Veratridine significantly enhanced the 0.5, 1, 2 and 3 vol% halothane-induced contracture and induced a negative inotropic effect in MH-susceptible muscle bundles. R increased by nearly 90% indicating that the combined effects were more pronounced in the relaxation phase. In MH non-susceptible muscle, veratridine did not significantly enhance the effects of halothane. CONCLUSIONS: These results on cut MH-susceptible human muscle bundles support the hypothesis that halothane-induced contracture in MH can be modified by the binding of an inhibitor of sodium channel inactivation.

Halothane induces calcium release from human skinned masseter muscle fibers.

BACKGROUND: An increase in masseter muscle tone in response to halothane or succinylcholine anesthesia (or both) can be observed in healthy persons. Thus the authors compared the fiber-type halothane and succinylcholine sensitivities in human masseter and vastus lateralis muscles. METHODS: Masseter and vastus lateralis muscle segments were obtained from 13 and 9 healthy persons, respectively. After chemical skinning of a single fiber and loading the sarcoplasmic reticulum with Ca++ 0.16 microM solution, halothane (0.5-4 vol% bubbled in the incubating solution), succinylcholine (0.1 microM to 10 mM), or both sensitivities were defined as the concentration inducing more than 10% of the maximum tension obtained by application of 16 microM Ca++ solution. The myofilament response to Ca++ was studied with and without halothane by observing the isometric tension of skinned masseter fibers challenged with increasing concentrations of Ca++. Muscle fiber type was determined by the difference in strontium-induced tension measurements. RESULTS: A significant difference in halothane sensitivity was found between type 1 masseter fibers (0.6+/-0.2 vol%; mean +/- SD) versus type 1 (2.7+/-0.6 vol%) and type 2 vastus lateralis muscle (2.5+/-0.4 vol%). Succinylcholine did not induce Ca++ release by the sarcoplasmic reticulum. In the masseter muscle, 0.75 vol% halothane decreased the maximal activated tension by 40% but did not change the Ca++ concentration that yields 50% of the maximal tension. CONCLUSIONS: The very low halothane threshold for Ca++ release from the masseter muscle usually could be counteracted by a direct negative inotropic effect on contractile proteins. However, halothane may increase the sensitivity of the sarcoplasmic reticulum Ca++ release to succinylcholine-induced depolarization, leading to an increase in masseter muscle tone.

Diltiazem and nifedipine reduce the in vitro contracture response to halothane in malignant hyperthermia-susceptible muscle.

The effects of diltiazem (1 microM) and nifedipine (1 microM) were examined separately on the in vitro halothane tests for malignant hyperthermia (MH) susceptibility. Eighteen patients with MH susceptibility were diagnosed as MH-susceptible (MHS) according to the protocol of the European MH Group. In addition, halothane tests were carried out in the presence of either diltiazem (ten patients) or nifedipine (eight patients). These two calcium channel blockers significantly reduced the halothane contracture. Furthermore, in five of the ten MHS patients tested in the presence of diltiazem as well as in five of the eight MHS patients tested in the presence of nifedipine the halothane contracture test could be classified as negative. It is concluded that the presence of clinical concentrations of either diltiazem or nifedipine in the muscle bath affects the in vitro discrimination for MH susceptibility to halothane.