Skeletal muscle sarcoplasmic reticulum in porcine malignant hyperthermia

Abnormal uptake and release of Ca 2+ ions from human malignant hyperthermia-susceptible sarcoplasmic reticulum 1 1Abbreviations: CICR, Ca2+-induced Ca2+ release; HEK-293, human embryonic kidney; HSR, heavy sarcoplasmic reticulum; IVCT, in vitro caffeine halothane contracture test; MH, malignant hyperthermia; MHS, malignant hyperthermia-susceptible; MHN, malignant hyperthermia normal; MOPS, 3-[N-Morpholino]propanesulphonic acid; RYR1, ryanodine receptor skeletal muscle gene; and TFP, trifluoperazine

Malignant hyperthermia (MH) is a pharmacogenetic myopathy that occurs in humans and several other mammalian species. There has been limited investigation of Ca2+ transport by human heavy sarcoplasmic reticulum (HSR) vesicles despite the fact that mutations of the ryanodine receptor Ca2+ release channel have been linked to inheritance of MH. In this study, the Ca2+ release and uptake mechanisms in human MH-susceptible HSR (MHS) vesicles were investigated and the kinetics and sensitivity compared to normal vesicles. Alterations in Ca2+ regulation were thereby elucidated. HSR vesicles from 6 normal (MHN) and 5 MHS patients were compared using a dual-wavelength continuous Ca2+ flux assay in the presence of pyrophosphate. The loading capacity and loading rate of Ca2+ in MHS vesicles were reduced by almost 50%. These parameters were restored to normal when the Ca2+ channel blocker ruthenium red was added. Calcium-induced calcium release, halothane-induced calcium release, and trifluoperazine-induced calcium release were clearly elevated in MHS HSR vesicles compared to MHN vesicles. The results suggest that MH ryanodine receptors exist in a more open resting state than those in normal muscle.

Xenon does not induce contracture in human malignant hyperthermia muscle

Xenon has many characteristics of an ideal anaesthetic agent. It is not known whether xenon is a safe alternative to the potent inhalational anaesthetics in patients susceptible to malignant hyperthermia (MH). We investigated the effect of xenon, halothane and caffeine on muscle specimens of 31 individuals, referred to the MH Unit of the University of Ulm, and performed genetic epidemiology. Thirteen individuals were classified as MH susceptible and 18 as MH negative. Xenon 70% did not cause an increase in baseline tension of any MH-susceptible muscle specimen in contrast to halothane and caffeine. The evoked twitch response increased transiently in MH-susceptible and normal specimens indicating a mechanism independent of MH susceptibility. These results suggest that xenon, in concentrations up to 70% may be a safe anaesthetic for MH-susceptible patients.

Hexanol and lidocaine affect the oligomeric state of the Ca-ATPase of sarcoplasmic reticulum

Hexanol at 7 degrees C stimulates the activity of the Ca-ATPase of sarcoplasmic reticulum (SR). Time-resolved phosphorescence spectroscopy studies of SR whose Ca-ATPase is covalently labeled with erythrosin isothiocyanate (ERITC) indicate that at 7 degrees C hexanol (1) cause a concentration-dependent increase in the rate of decay of phosphorescence anisotropy, (2) causes larger oligomers of Ca-ATPase to dissociate into smaller oligomers, and (3) increases the rotational mobility of Ca-ATPase in all its oligomeric states. Electron paramagnetic resonance (EPR) spectroscopy of spin-labeled stearic acid (SASL) in SR suggests that at 7 degrees C hexanol diminishes the fraction of SR lipids in the boundary lipid domain and disorders and fluidizes both the boundary lipid and the unrestricted lipid domain. In protein-free liposomes of extracted SR lipids hexanol increases fluidity and decreases order to a greater extent near the center of the lipid bilayer than near the polar head groups. At 25 degrees C hexanol has biphasic effects on Ca-ATPase activity: at 10 and 20 mM hexanol increases activity, but at 30 mM and especially at 40 mM there is inhibition of Ca-ATPase activity. The influence of hexanol at 25 degrees C on the oligomeric state of Ca-ATPase is also biphasic. At 10 and 20 mM, hexanol promotes the dissociation of larger oligomers into smaller ones, whereas at higher concentrations, 30 and 40 mM, hexanol causes larger oligomers to be formed from smaller ones. Lidocaine at 25 degrees C inhibits Ca-ATPase activity and causes dramatic slowing of the decay of phosphorescence anisotropy of ERITC-labeled SR by causing the formation of larger oligomers of Ca-ATPase from smaller ones. In protein-free liposomes of SR lipids at 25 degrees C, lidocaine disorders and fluidizes the acyl chains near the center of the bilayer (as did hexanol), but has opposite effects near the polar head groups. The opposite effects of hexanol and lidocaine on the oligomeric state of the SR Ca-ATPase provide a new molecular explanation for the opposite effects of hexanol and lidocaine on the activity of the Ca-ATPase. We conclude that the biphasic effects of hexanol on the activity of Ca-ATPase can be accounted for by biphasic effects of hexanol on the oligomeric state of the Ca-ATPase. This study supports the view that anesthetics can alter interactions between membrane proteins.

Impairment of ATP-linked reactions in mitochondria isolated from skeletal muscle of halothane-sensitive pigs

Oxygen consumption was depressed in mitochondria isolated from halothane sensitive pig (HP) muscle. The calculation of the respiratory control ratio (RCR) indicated that mitochondria were more affected at the site-I level of the respiratory chain. Calcium accumulation in these mitochondria was not altered when driven by the oxidation of succinate. This process was abolished when linked to ATP as a source of energy. ATP transport was completely inhibited in (HP) mitochondria.

Uptake and release of calcium ions by heavy sarcoplasmic reticulum fraction of normal and malignant hyperthermia-susceptible human skeletal muscle

1. Ca2+ uptake, Ca2(+)-dependent ATPase activity and halothane-induced Ca2+ release from the heavy sarcoplasmic reticulum fraction of muscle from malignant hyperthermia susceptible individuals are similar to those of normal human muscle. 2. Ca2(+)-induced Ca2+ release from the diseased muscle was increased by 13%.

Malignant hyperthermia: effects of halothane on the surface membrane

We studied the electrical properties of intact muscle fibers from normal and malignant hyperthermia-susceptible (MHS) pigs. Resting membrane potentials, action potentials, and current-voltage relationships were measured with and without the presence of halothane. There were no changes in the resting potentials or the specific membrane conductances at any concentration of halothane in either the normal or MHS fibers. The current-voltage relationships of normal and MHS fibers did not differ. Contractures were observed in MHS muscle when the concentration of halothane was greater than or equal to 0.8%. These halothane-induced contractures were not associated with depolarization of the surface membrane. Contractures were not observed in normal muscle even at concentrations of 6.0% halothane. In contrast, halothane altered the shape of the action potentials of both MHS and normal fibers. However, these changes were significantly greater in MHS fibers, occurred at much lower concentrations, and were partially prevented by preincubation in 10 microM dantrolene.

Porcine malignant hyperthermia: halothane effects on force generation in skeletal muscles

Halothane-induced malignant hyperthermia (MH) is thought to result from a defect in the regulation of cytosolic calcium concentration in MH-susceptible (MHS) skeletal muscle. Such a defect might be expected to alter the time course of contractile responses. To test this hypothesis, isolated intact cell bundles from external intercostal and common digital extensor muscles of normal and MHS pigs were stimulated electrically to elicit twitch and tetanic tension in the presence and absence of halothane (2.5%). Time intervals measured for both twitches and tetani were (1) the latent period between the stimulus and tension increase, (2) the time to peak tension, and (3) the half-relaxation time. In contrast to previous reports, halothane had no effect on any measured time course parameter of twitches of either type of normal or MHS muscle, nor did the twitches of MHS and normal muscles differ in any parameter in the absence of halothane. However, the tetanic tension relaxation in both types of MHS muscle was markedly slowed by halothane, whereas in normal muscles there was little change. The slower rate of relaxation induced by halothane in MHS muscles suggests that halothane, either directly or indirectly, enhances the release or slows the removal of calcium in intact MHS muscles following maximal activation. This slowed tetanus relaxation could be of use in identification of MHS individuals.

Involvement of the 60 kDa phosphoprotein in the regulation of Ca2+ release from sarcoplasmic reticulum of normal and malignant hyperthermia susceptible pig muscles

Junctional sarcoplasmic reticulum (SR) vesicles isolated from back muscles of normal and malignant hyperthermia susceptible (MHS) pigs were phosphorylated by addition of MgATP in the presence of 5 mM Ca2+ and 1 microM calmodulin (CaM). The major site of phosphorylation was a 60 kDa protein both in normal and MHS SR. The maximal amount of phosphorylation in MHS SR (5 pmol P/mg SR) was significantly lower than that in the normal SR (12 pmol P/mg SR). The phosphorylated 60 kDa protein was spontaneously dephosphorylated both in normal and MHS SR. Ca2+ release from the passively loaded SR was induced by a Ca2+-jump, and monitored by stopped-flow fluorometry using chlorotetracycline. In the absence of preincubation with MgATP, no significant difference was found in any of the kinetic parameters of Ca2+ release between normal and MHS SR. Upon addition of 20 microM MgATP to the passively loaded SR to phosphorylate the 60 kDa protein, the initial rate of Ca2+ release in normal SR significantly decreased from 659 +/- 102 to 361 +/- 105 nmol Ca2+/mg SR per s, whereas in MHS SR the rate decreased from 749 +/- 124 to 652 +/- 179 nmol Ca2+/mg SR per s. Addition of 20 microM adenosine 5'-[beta, gamma-imido]triphosphate (p[NH]ppA) did not significantly alter the initial rate of Ca2+ release both in normal and MHS SR. These results suggest that the previously reported higher Ca2+ release rate in MHS SR (Kim et al. (1984) Biochim. Biophys. Acta 775, 320-327) is at least partly due to the reduced extent of the Ca2+/CaM-dependent phosphorylation of the 60 kDa protein. Two-dimensional gel electrophoresis study showed that amount of a protein with Mr = 55,000 was significantly lower in MHS SR than in normal SR suggesting that the abnormally lower amount of 55 kDa protein would cause the lower amount of phosphorylation of the 60 kDa protein in MHS SR.

Fura-2 detected myoplasmic calcium and its correlation with contracture force in skeletal muscle from normal and malignant hyperthermia susceptible pigs

Fura-2 was used to estimate myoplasmic [Ca2+] in intact intercostal muscle fibers from normal and malignant hyperthermia susceptible (MHS) pigs. Small muscle bundles (20-50 fibers) were loaded with the membrane-permeant form of the dye. Resting myoplasmic [Ca2+] were not significantly different in normal and MHS muscles. Halothane produced increases in myoplasmic Ca2+ with associated contractures in MHS muscles, but not in normal muscles. These halothane effects were reversible. Caffeine produced increases in myoplasmic Ca2+ and contractures in both MHS and normal muscles. The threshold concentrations were lower in the MHS muscles. The correlations between myoplasmic [Ca2+] and force in MHS and normal muscles were similar.

Skeletal muscle contraction characteristics in vivo in malignant hyperthermia susceptible subjects

Ten malignant hyperthermia susceptible (MHS) subjects were investigated, all of them positive in in vitro tests. As a control group 12 healthy subjects were investigated. The investigation was done in a blind fashion during strictly standardized conditions. Electromechanical delay of contraction and half contraction time to tetanus were faster (P less than 0.05) while half relaxation time was shorter in the MHS subjects (P less than 0.05). Skin and intramuscular temperature were significantly higher in the MHS subjects (P less than 0.05). This indicates that MHS subjects differ in various skeletal muscle characteristics during "normal" conditions. Further studies to define the temperature level at which the test of muscle function is most discriminating are needed before it can be used for diagnostic purposes.

Ligand and lipid domain stabilization of a membraneous Ca2+-ATPase during hyperthermia

The susceptibility of the membranous Ca2+-ATPase of sarcoplasmic reticulum to enzymatic inactivation at hyperthermic temperatures was investigated. Inactivation produced a break in the Arrhenius plot at 45-46 degrees C and was accompanied by an increased mobility of spin label, covalently attached to the Ca2+-ATPase. MgADP and MgATP exerted a markedly stabilizing effect on inactivation, both at pH 7.0 and in acidic media. By contrast, high-affinity Ca2+ or Mg2+ binding only moderately stabilized Ca2+-ATPase (inactivation rates were decreased 2-3 times), and this effect was non-additive, i.e., only observed in the absence of the other divalent cation. But withdrawal of K+ and Na+ gave rise to a pronounced destabilization that could be reversed efficiently by high concentrations of Ca2+ or Mg2+. These results are compared with a previous study on detergent solubilized Ca2+-ATPase (Møller, J.V., Lind, K.E. and Andersen, J.P. (1980) J. Biol. Chem. 255, 1912-1920) which showed the enzyme to be markedly stabilized by Ca2+ as well as by nucleotide. It is concluded that, due to the presence of nucleotide, inactivation of Ca2+-ATPase is not likely to occur during malignant hyperthermia and that the native environment of the lipid bilayer provides stabilization of the membrane-embedded and Ca2+-translocating domain of the Ca2+-ATPase.

Malignant hyperthermia

Malignant hyperthermia is a hereditary trait characterized by hypercatabolic reactions induced by anesthetic drugs, or physical or emotional stress. Patients must be treated quickly and efficiently in order to prevent irreversible organ damage and death.

The effects of chlorbutol on skeletal muscle sarcoplasmic reticulum function in porcine malignant hyperpyrexia

1. Chlorbutol, a muscle relaxant, inhibits the in vitro muscle hypercontractility which is characteristic of the anaesthetic complication, malignant hyperpyrexia (MH). 2. Studies on isolated sarcoplasmic reticulum vesicles have shown that this effect of chlorbutol in MH is not due to a modification of Ca2+-transport mechanisms.

The effects of calmodulin antagonist drugs on isolated sarcoplasmic reticulum from malignant hyperpyrexia susceptible swine

1. Because calcium antagonist drugs increase contracture in both control and malignant hyperpyrexia susceptible (MHS) skeletal muscle, the effect of these drugs on the sarcoplasmic reticulum (SR) was investigated. 2. The calmodulin antagonist drugs inhibited the Ca2+ dependent ATPase activity and the ATP-dependent Ca2+ uptake, and accelerated the efflux of Ca2+ from isolated SR preparations from both control and MHS skeletal muscle. These effects of calmodulin antagonist drugs on SR Ca2+ transport functions were consistent with their in vitro pharmacological effects on control and MHS muscle.

Thiophosphorylation of skeletal muscle sarcoplasmic reticulum in porcine malignant hyperpyrexia

1. The basal, Ca2+-dependent and Mg2+-dependent thiophosphorylation of malignant hyperpyrexia-susceptible (MHS) porcine skeletal muscle was investigated. 2. Seven major proteins of Mr 100,000-11,000 were substrates for thiophosphorylation. 3. Sodium molybdate significantly elevated all levels of thiophosphorylation in control sarcoplasmic reticulum, but did not effect the Ca2+-dependent thiophosphorylation of MHS samples. 4. These results suggest that MHS sarcoplasmic reticulum may have altered sensitivity to protein phosphatase inhibition.

Enhanced Ca2+-induced calcium release by isolated sarcoplasmic reticulum vesicles from malignant hyperthermia susceptible pig muscle

To further define the possible involvement of sarcoplasmic reticulum calcium accumulation and release in the skeletal muscle disorder malignant hyperthermia (MH), we have examined various properties of sarcoplasmic reticulum fractions isolated from normal and MH-susceptible pig muscle. A sarcoplasmic reticulum preparation enriched in vesicles derived from the terminal cisternae, was further fractionated on discontinuous sucrose density gradients (Meissner, G. (1984) J. Biol. Chem. 259, 2365-2374). The resultant MH-susceptible and normal sarcoplasmic reticulum fractions, designated F0-F4, did not differ in yield, cholesterol and phospholipid content, or nitrendipine binding capacity. Calcium accumulation (0.27 mumol Ca/mg per min at 22 degrees C), Ca2+-ATPase activity (0.98 mumol Pi/mg per min at 22 degrees C), and calsequestrin content were also similar for MH-susceptible and normal sarcoplasmic reticulum fraction F3. To examine sarcoplasmic reticulum calcium release, fraction F3 vesicles were passively loaded with 45Ca (approx. 40 nmol Ca/mg), and rapidly diluted into a medium of defined Ca2+ concentration. Upon dilution into 1 microM Ca2+, the extent of Ca2+-dependent calcium release measured after 5 s was significantly greater for MH-susceptible than for normal sarcoplasmic reticulum, 65.9 +/- 2.8% vs. 47.7 +/- 3.9% of the loaded calcium, respectively. The C1/2 for Ca2+ stimulation of this calcium release (5 s value) from MH-susceptible sarcoplasmic reticulum also appeared to be shifted towards a higher Ca2+-sensitivity when compared to normal sarcoplasmic reticulum. Dantrolene had no effect on calcium release from fraction F3, however, halothane (0.1-0.5 mM) increased the extent of calcium release (5 s) similarly in both MH-susceptible and normal sarcoplasmic reticulum. Furthermore, Mg2+ was less effective at inhibiting, while ATP and caffeine were more effective in stimulating, this Ca2+-dependent release of calcium from MH-susceptible, when compared to normal sarcoplasmic reticulum. Our results demonstrate that while sarcoplasmic reticulum calcium-accumulation appears unaffected in MH, aspect(s) of the sarcoplasmic reticulum Ca2+-induced calcium release mechanism are altered. Although the role of the Ca2+-induced calcium release mechanism of sarcoplasmic reticulum in situ is not yet clear, our results suggest that an abnormality in the regulation of sarcoplasmic reticulum calcium release may play an important role in the MH syndrome.

Porcine malignant hyperthermia: cell injury enhances halothane sensitivity of biopsies

A possible relationship between muscle cell injury or deterioration and enhanced halothane sensitivity was studied by monitoring mechanical responses of skeletal muscles from normal pigs and pigs susceptible to malignant hyperthermia (MH). Increased time postbiopsy and decreased maximum control tetanic tension both correlated significantly with enhanced sensitivity to halothane. In both normal and MH-susceptible (MHS) muscles, greater halothane sensitivity was observed in cut cell than in intact cell bundles and in low tetanic tension as compared to high tension preparations. Subsequent to halothane exposure, twitches of high tension (greater than or equal 1.75 kg . cm-2) intact bundles of both normal and MHS muscles were potentiated. Tetani of normal intact bundles were not altered, whereas those of MHS bundles were depressed after halothane exposure. Control twitch-to-tetanus ratios (twitch ratios) were higher in MHS (0.23) than in normal (0.12) intact bundles. According to discriminant analysis, the best distinction between normal and MHS muscles, either cut or intact, was obtained by comparing halothane-induced changes in tetanic tension and control twitch ratios.

Effect of halothane on Ca2+-induced Ca2+ release from sarcoplasmic reticulum vesicles isolated from rat skeletal muscle

Halothane induces the release of Ca2+ from a subpopulation of sarcoplasmic reticulum vesicles that are derived from the terminal cisternae of rat skeletal muscle. Halothane-induced Ca2+ release appears to be an enhancement of Ca2+-induced Ca2+ release. The low-density sarcoplasmic reticulum vesicles which are believed to be derived from nonjunctional sarcoplasmic reticulum lack the capability of both Ca2+-induced and halothane-induced Ca2+ release. Ca2+ release from terminal cisternae vesicles induced by halothane is inhibited by Ruthenium red and Mg2+, and require ATP (or an ATP analogue), KCl (or similar salt) and extravesicular Ca2+. Ca2+-induced Ca2+ release has similar characteristics.

Malignant hyperthermia: molecular defects in membrane permeability

Malignant hyperthermia (MH), a genetically inherited disorder of skeletal muscle, is due to molecular defect in membrane permeability. The alteration in membrane permeability is suggested to be due to enhanced phospholipase A2 activity which is responsible for the increased level in sarcoplasmic Ca2+. The excess Ca2+ is responsible for muscle hyper-rigidity and enhanced rate of glycolysis, resulting in a rapid rate of lactic acid production and a low pH in MH muscle.

Kinetic studies of Ca2+ release from sarcoplasmic reticulum of normal and malignant hyperthermia susceptible pig muscles

The time-course of Ca2+ release from sarcoplasmic reticulum isolated from muscles of normal pigs and those of pigs susceptible to malignant hyperthermia were investigated using stopped-flow spectrophotometry and arsenazo III as a Ca2+ indicator. Several methods were used to trigger Ca2+ release: (a) addition of halothane (e.g., 0.2 mM); (b) an increase of extravesicular Ca2+ concentration ([Ca2+0]); (c) a combination of (a) and (b), and (d) replacement of ions (potassium gluconate with choline chloride) to produce membrane depolarization. The initial rates of Ca2+ release induced by either halothane or Ca2+ alone, or both, are at least 70% higher in malignant hyperthermic sarcoplasmic reticulum than in normal. The amount of Ca2+ released by halothane at low [Ca2+0] in malignant hyperthermic sarcoplasmic reticulum is about twice as large as in normal sarcoplasmic reticulum. Membrane depolarization led to biphasic Ca2+ release in both malignant hyperthermic and normal sarcoplasmic reticulum, the rate constant of the rapid phase of Ca2+ release induced by membrane depolarization being significantly higher in malignant hyperthermic sarcoplasmic reticulum (k = 83 s-1) than in normal (k = 37 s-1). Thus, all types of Ca2+ release investigated (a, b, c and d) have higher rates in malignant hyperthermic sarcoplasmic reticulum than normal sarcoplasmic reticulum. These results suggest that the putative Ca2+ release channels located in the sarcoplasmic reticulum are altered in malignant hyperthermic sarcoplasmic reticulum.

Dantrolene and calcium uptake by the sarcoplasmic reticulum of malignant hyperpyrexia-susceptible pigs

Sarcoplasmic reticulum membranes were isolated from the skeletal muscle of pigs susceptible or resistant to the anaesthetic complication malignant hyperpyrexia. The skeletal muscle relaxant dantrolene was shown to be without effect on the Ca2+ -dependent ATPase activity of either sarcoplasmic reticulum preparation. The active transport of calcium by sarcoplasmic reticulum from both sources was also unaffected by the presence of dantrolene. These findings indicate that dantrolene does not exert its pharmacological action in skeletal muscle by stimulating calcium uptake by the sarcoplasmic reticulum.

Calcium-induced Ca2+ release from sarcoplasmic reticulum of pigs susceptible to malignant hyperthermia. The effects of halothane and dantrolene

Calcium-induced calcium release and halothane-induced calcium release from pig sarcoplasmic reticulum (SR) were studied. The SR prepared from pigs susceptible to malignant hyperthermia (MH) was shown to release calcium at a much lower level of calcium content than in normal pig SR. The concentration above which halothane can release calcium is 40 microM for both MH-SR and normal SR, although the latter required a high calcium content to demonstrate the calcium release. Dantrolene was shown to inhibit the halothane-induced calcium release. Results suggest that SR plays an important role in pathogenesis of MH.

Abnormality in calcium release from skeletal sarcoplasmic reticulum of pigs susceptible to malignant hyperthermia

Two fractions of sarcoplasmic reticulum, one light (LSR) and one heavy (HSR), were isolated from gracilis muscle of control and malignant hyperthermia (MH)-susceptible pigs. Part of the gracilis muscle biopsy was used to compare the contracture sensitivity of the muscle to the calcium-releasing effects of caffeine on isolated SR membranes. Gracilis muscle of MH pigs was more sensitive to the contracture-producing effects of caffeine than control pig muscle. The caffeine dose-cumulative contracture response curve for MH muscle was shifted left of that for controls. The amount of caffeine-induced calcium released from SR is a function of the amount of calcium preload and this did not differ between LSR of MH and control muscle. When LSR fractions were optimally loaded with calcium for caffeine-induced calcium release, no difference in calcium-releasing effects of varying caffeine doses was observed between MH and control LSR. At calcium preloads below optimal, the MH-LSR appeared to be more sensitive to caffeine-induced calcium release. The HSR fractions could not be loaded with calcium in a manner similar to the LSR fractions because of an apparent calcium-induced calcium release phenomenon. Therefore, calcium threshold for calcium-induced calcium release was compared between MH and control HSR fraction. The effect of caffeine on the calcium-induced calcium release was also studied. The average calcium concentration threshold for calcium-induced calcium release was markedly lower for MH vs. control HSR; 20 vs. 63 nmol Ca2+/mg, respectively. Caffeine decreased the threshold for calcium-induced calcium release more in the MH than in control HSR. Under all conditions studied, the amount of calcium released did not differ between the two groups. Ruthenium red increased the threshold calcium concentration for calcium-induced calcium release while it reduced the amount of calcium released. Increasing concentrations of Mg2+ increased the Ca2+ threshold for release and the amount of Ca2+ released but did not significantly affect rate of Ca2+ release. Results of the study suggest a defect in the mechanisms causing calcium release from SR in MH-affected muscle.

The effect of dantrolene on skeletal-muscle sarcoplasmic-reticulum function in malignant hyperpyrexia in pigs

The effect of the muscle relaxant dantrolene on isolated sarcoplasmic reticulum was studied in control and malignant-hyperpyrexia-susceptible Landrace pigs. The membranes prepared from both sources showed similar Ca2+-dependent ATPase activities, had comparable phospholipid/protein ratios, and their sodium dodecyl sulphate/polyacrylamide-gel patterns were indistinguishable. Membranes from both sources appeared to bind similar amounts of dantrolene. The drug did not stimulate Ca2+-dependent ATPase activity in preparations from either source. The rates of Ca2+ exchange and Ca2+ efflux appeared to be similar in sarcoplasmic reticulum of control and malignant-hyperpyrexia-susceptible pigs. Dantrolene did not affect either the rates or the amount of Ca2+ lost from the vesicles. These results suggest that dantrolene does not directly affect the movement of Ca2+ across the sarcoplasmic-reticulum membrane.

The isolation and chemical characterization of skeletal muscle microsomes from swine susceptible to malignant hyperpyrexia

1. The anaesthetic complication malignant hyperpyrexia (MH) occurs in individuals and swine with a muscle membrane abnormality. 2. In an attempt to characterize this abnormality, the lipid and protein composition of muscle membranes from MH-susceptible swine was examined and compared with controls. 3. No significant abnormality in the membrane protein or lipid content of MH-susceptible muscle was detected.

Porcine muscle responses to carbachol, alpha- and beta-adrenoceptor agonists, halothane or hyperthermia

1. Whole body trans-section at the level of the first or second lumbar vertebra of stress-susceptible or normal Poland China swine provided a preparation of isolated perfused caudal muscle that was without nervous or hormonal influences. Metabolic responses to halothane anaesthesia were exaggerated in the susceptible preparation. 2. Carbachol (10(-4) M) increased O2 consumption threefold and elevated blood lactate levels from 3 to 8 mumole/ml. in susceptible but not in normal muscle preparations. 3. Isoprenaline in a continuous infusion (2.5 micrograms/kg caudal wt. per min for 12 min, subsequently diminished to 1.2 microgram/kg per min) did not increase O2 consumption of susceptible or normal muscle but did increase blood lactate by 2 mumole/ml. in both. 4. Simultaneous administration of carbachol and isoprenaline resulted in additive increases in blood lactate. 5. Incremental increases in temperature above 41 degrees C initiated exaggerated increases in O2 consumption and blood lactate in susceptible but not normal muscle; these were similar to whole body responses. 6. Phenylephrine (0.2-25 micrograms/kg per min continuous) produced (i) hypertension, (ii) no observed effects upon aerobic or anaerobic metabolism and (iii) progressive tissue oedema; these effects were similar in susceptible and normal muscle. 7. Skeletal muscle from stress-susceptible swine is evidently inherently capable of metabolic responses to cholinergic agonists and increased temperature; these responses are greater than those in normal muscle. This suggests that initiation of stress responses in intact swine is related to somatic motor and sympathetic stimulation of abnormal skeletal muscle, and not to a disorder of the somatic or sympathetic nervous system.