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We have cloned and sequenced the cDNA encoding triadin, a junctional terminal cisternae protein from human skeletal muscle. The cDNA, 2941 base pairs in length, encodes a protein of 729 amino acids with a predicted molecular mass of 81,545 Da. Hydropathy analysis indicates that triadin of human skeletal muscle has the same topology in the myoplasmic, transmembrane and sarcoplasmic reticulum luminal domains as that of triadin from rabbit skeletal muscle. The number and relative position of potential modulation sites are also conserved between the human and rabbit proteins. The cDNA sequence of the predicted sarcoplasmic reticulum luminal domain of human triadin diverged from that of rabbit, with an observed similarity of 82%, translating to an identity of 77% in amino acid sequence. Two insertions of 9 and 12 residues in the amino acid sequence were observed in the predicted luminal domain of triadin, although the structural and functional consequences of such insertions are expected to be minimal. Using fluorescence in situ hybridisation, we have assigned the gene encoding human triadin to the long arm of chromosome 6 in the region 6q22-6q23. Our structural analysis of human triadin supports a central role for this protein in the mechanism of skeletal muscle excitation/contraction coupling.

In soluble and particulate extracts from muscle D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and D-myo-inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] are metabolised stepwise to inositol. Ins(1,4,5)P3 is rapidly dephosphorylated to D-myo-inositol 1,4-bisphosphate then to D-myo-inositol 4-phosphate and finally inositol. In soluble extracts Ins(1,3,4,5)P4 is dephosphorylated to D-myo-inositol 1,3,4-trisphosphate then sequentially to D-myo-inositol 3,4-bisphosphate, D-myo-inositol 3-phosphate and inositol, while in particulate extracts D-myo-inositol 1,3-bisphosphate is the predominant inositol bisphosphate formed. Dephosphorylation of these inositol polyphosphates is Mg2+ dependent and inhibited by D-2,3-bisphosphoglyceric acid. Ins(1,4,5)P3 is also phosphorylated to form Ins(1,3,4,5)P4 in soluble extracts by Ins(1,4,5)P3 3-kinase. Ins(1,4,5)P3 3-kinase activity is Mg2+ and ATP dependent and is stimulated by Ca2+ and calmodulin. Particulate (sarcotubular) inositol polyphosphate 5-phosphatase (5-phosphatase) is found in membranes which are intimately involved in excitation-contraction coupling and the generation of the primary Ca2+ signal of muscle cells. Particulate 5-phosphatase had the highest specific activity in the transverse-tubule membrane, when compared to the terminal cisternae and longitudinal-tubule membranes of the sarcoplasmic reticulum. Particulate Ins(1,3,4,5)P4-3-phosphatase activity was also detected after fractionation of solubilised sarcotubular membranes by DEAE-Sephacel. Particulate 5-phosphatase activity was purified 25,600-fold to a specific activity of 25.6 mumol Ins(1,4,5)P3 hydrolysed.min-1.mg protein-1, after DEAE-Sephacel and novel affinity chromatography using D-2,3-bisphosphoglycerate/agarose and Sepharose-4B-immobilised Ins(1,4,5)P3-analog matrices. Purified particulate 5-phosphatase had apparent Km of 46.3 microM and 1.9 microM and Vmax of 115 and 0.046 mumol substrate hydrolysed.min-1.mg protein-1, for Ins(1,4,5)P3 and Ins(1,3,4,5)P4, respectively. In contrast, purified soluble type I 5-phosphatase had apparent Km of 8.9 microM and 1.1 microM and Vmax of 3.55 and 0.13 mumol substrate hydrolysed.min-1.mg protein-1, for Ins(1,4,5P3 and Ins(1,3,4,5)P4, respectively. As in other cells, muscle 5-phosphatases have a lower affinity, but a higher capacity to metabolise Ins(1,4,5)P3 than Ins(1,3,4,5)P4. Soluble type I 5-phosphatase may have a functional role in the metabolism of both inositol polyphosphates, while particulate 5-phosphatase may primarily metabolise Ins(1,4,5)P3. Purified Ins(1,4,5)P3 3-kinase had an apparent Km of 0.42 microM and a Vmax of 4.12 nmol Ins(1,4,5)P3 phosphorylated.min-1.mg protein-1. The profile of inositol polyphosphate metabolism in muscle is similar to that reported in other tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

The ability of the novel D- myo -inositol 1,4,5-trisphosphate [Ins(1,4,5)P 3 ] analogues, L- chiro -inositol 1,4,6-trisphosphate [L- chr Ins(1,4,6)P 3 ] and the corresponding trisphosphorothioate compound [L- chr Ins(1,4,6)PS 3 ] to inhibit soluble inositol (1,4,5)P 3 /(1,3,4,5)P 4 -polyphosphate 5-phosphatase, potently and selectively, has been investigated. L- chr Ins(1,4,6)P 3 competitively inhibited 5-phosphate specific dephosphorylation of Ins(1,4,5)P 3 and inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P 4 ] with apparent K i values of 6.35 and 1.76 μM, respectively. L- chr Ins(1,4,6)PS 3 competitively inhibited hydrolysis of Ins(1,4,5)P 3 and noncompetitively inhibited dephosphorylation of Ins(1,3,4,5)P 4 with apparent K i values of 0.67 and 0.44 μM, respectively. L- chr Ins(1,4,6)PS 3 did not affect Ins(1,4,5)P 3 3-kinase activity. In the present investigation L- chr Ins(1,4,6)P 3 and L- chr Ins(1,4,6)PS 3 have been shown to be the most potent and selective inhibitors of inositol polyphosphate metabolism yet described.

The diagnosis of an acute malignant hyperthermia reaction by clinical criteria can be difficult because of the nonspecific nature and variable incidence of many of the clinical signs and laboratory findings. Development of a standardized means for estimating the qualitative likelihood of malignant hyperthermia in a given patient without the use of specialized diagnostic testing would be useful for patient management and would promote research into improved means for diagnosing this disease.Using the Delphi method and an international panel of 11 experts on malignant hyperthermia, a multifactor malignant hyperthermia clinical grading scale comprising standardized clinical diagnostic criteria was developed for classification of existing records and for application to new patients.This scale ranks the qualitative likelihood that an adverse anesthetic event represents malignant hyperthermia (malignant hyperthermia event rank) and that, with further investigation of family history, an individual patient will be diagnosed as malignant hyperthermia susceptible (malignant hyperthermia susceptibility rank). The assigned rank represents a lower bound on the likelihood of malignant hyperthermia. The clinical grading scale requires the anesthesiologist to judge whether specific clinical signs are appropriate for the patient's medical condition, anesthetic technique, and surgical procedure.The malignant hyperthermia clinical grading scale is recommended for use as an aid to the objective definition of this disease. It use may improve malignant hyperthermia research by allowing comparisons among well-defined groups of patients. This clinical grading system provides a new and comprehensive clinical case definition for the malignant hyperthermia syndrome.

SUMMARY 1. Azumolene sodium is a new water-soluble derivative of dantrolene sodium that also acts as a skeletal-muscle relaxant. 2. Azumolene (6 μmol/L) inhibited the hypercontractility induced separately by 3% halothane, 2 mmol/L caffeine and 80 mmol/L potassium chloride in isolated malignant hyperpyrexia (MH)-susceptible muscle. Azumolene was equipotent with dantrolene in inhibiting the abnormal responses. 3. Like dantrolene, azumolene (6 μmol/L) not only prevented but reversed the abnormal contractures induced by halothane and caffeine. Contracture responses to caffeine were also modified by azumolene in control preparations. 4. In the presence of maximal effective concentrations of dantrolene, azumolene failed to further relax caffeine-induced contractures, and the converse was also true. This was observed in both MH-susceptible and control preparations. 5. Sarcoplasmic reticulum Ca2+-dependent ATPase activity from MH-susceptible and control muscle was not affected by azumolene. 6. Like dantrolene, azumolene may inhibit Ca2+ release directly from the sarcoplasmic reticulum and be of therapeutic value for the treatment of MH.

Seven out of eight piglets which were susceptible to malignant hyperthermia (MHS) died when subjected to a heat challenge which was well tolerated by controls. The piglets which succumbed developed the classical clinical and biochemical changes of malignant hyperthermia before they died. These results show that overheating alone can trigger malignant hyperthermia in susceptible animals. Because the biochemical basis of malignant hyperthermia is similar in both humans and pigs, these observations suggest that overheating can also trigger malignant hyperthermia in humans. The susceptibility to overheating in malignant hyperthermia susceptible humans and animals probably explains why the myopathy which predisposes to this condition has also been reported to predispose to heat-stroke and the sudden infant death syndrome. In view of this, particular care to prevent overheating should be taken in infants of parents who are susceptible to malignant hyperthermia.

We classify malignant hyperthermia (MH) into the three myopathies that predispose to the anesthetic complication. These are as follow.

A myoplasmic 3-kinase was detected in porcine skeletal muscle that phosphorylated [3H]Ins(1,4,5)P3 [D-myo-inositol(1,4,5)trisphosphate] to [3H]Ins(1,3,4,5)P4 [D-myo-inositol(1,3,4,5)tetrakisphosphate]. The Ins(1,4,5)P3 3-kinase activity was ATP- and Mg(2+)-dependent, and was activated by Ca2+ and calmodulin. Ins(1,4,5)P3 3-kinase activity was purified 2632-fold from soluble extracts of skeletal muscle by a combination of DEAE-Sephacel, heparin-Agarose and Ins(1,4,5)P3 structural-analogue affinity chromatography. The highest specific activity obtained was 10.6 nmol of Ins(1,4,5)P3 phosphorylated/min/mg protein. The partially purified enzyme had a mean Km and Vmax of 0.46 microM and 3.15 nmol/min/mg protein for Ins(1,4,5)P3 metabolism, respectively. After analytical gel filtration two forms of soluble Ins(1,4,5)P3 3-kinase were observed with M(r) of 39,000 and 62,000. As in other cell types, muscle Ins(1,4,5)P3 3-kinase was soluble, and had a higher affinity but a lower capacity to metabolize Ins(1,4,5)P3 in comparison to Ins(1,4,5)P3 5-phosphatase.

1. The calcium channel antagonists verapamil (100 microM) and nifedipine (100 microM) inhibited twitch response and KCl induced hypercontractility in malignant hyperpyrexia (MH)-susceptible porcine skeletal muscle. These calcium channel antagonists did not effect hypercontractility induced by 3% halothane or 2 mM caffeine. 2. The calcium channel agonist BAY K 8644 (50 microM) induced contracture in MH-susceptible muscle but did not potentiate contracture response induced by 2 mM caffeine or 3% halothane. BAY K 8644 did not increase the resting tension of control muscle or increase the sensitivity of control muscle to 4 mM caffeine, 3% halothane or 80 mM KCl. 3. The sarcoplasmic reticulum (SR) from MH-susceptible and control porcine skeletal muscle was separated into vesicular fractions enriched in the membrane elements of the terminal cisternae and longitudinal tubules. 4. Verapamil and diltiazem [which has been previously shown to inhibit the hypercontractility of MH-susceptible porcine muscle to caffeine, halothane and KCl (Foster and Denborough, 1989 Br. J. Anaesth. 62, 566-572)] did not effect Ca2+ uptake or Ca(2+)-dependent ATPase activities of SR longitudinal tubule membranes, from MH-susceptible or control muscle. These calcium channel antagonists did not effect Ca2+ release from terminal cisternae preparations. 5. The skeletal muscle relaxant dantrolene inhibited Ca2+ efflux and equilibrium-Ca2+ exchange associated with the terminal cisternae membrane of MH-susceptible and control skeletal muscle. 6. Calcium channel antagonists modify Ca2+ fluxes in MH-susceptible and control muscle by acting at a site distal to the SR. Calcium channel antagonists may inhibit contractile response by modifying events of excitation-contraction coupling associated with the voltage sensor molecule (dihydropyridine-receptor) of the transverse-tubule membrane, whereas dantrolene directly acts on the terminal cisternae membrane to inhibit Ca2+ efflux and equilibrium Ca2+ exchange. Different calcium channel antagonists seem to modify the voltage-sensor mechanism in different ways in MH-susceptible muscle. 7. An abnormality in the coupling mechanism of the voltage sensor-SR calcium release channel may exist in MH-susceptible muscle. This dysfunction may be an adaptation to the elevated levels of myoplasmic Ca2+ and/or the molecular defect described in the Ca2+ release channel of the SR of MH-susceptible porcine muscle. In view of these results it is unlikely that nifedipine or verapamil would be of therapeutic value for the treatment of MH.

1. Malignant hyperpyrexia (MH) is an inherited muscle abnormality that presents clinically as a syndrome of life-threatening complications during general anaesthesia. 2. Propofol is a new sedative hypnotic used for the induction and maintenance of anaesthesia. 3. Propofol did not induce MH in five susceptible pigs. Propofol did not induce contracture in isolated MH susceptible muscle but did modify halothane, caffeine and KCl contractures.

The molecular defect predisposing to the majority of malignant hyperthermia (MH) cases is unknown, although various point mutations in the ryanodine receptor gene (RYR1) have been associated with susceptibility in a small proportion of cases. We report here that one of these, the Arg163Cys substitution, does not cosegregate with MH susceptibility. Comparison of cDNA sequences encoding the skeletal muscle specific components of the dihydropyridine receptor alpha 1 subunit between MH susceptible (MHS) and MH non-susceptible (MHN) patients was made in subjects without the reported MH linked RYR1 mutations. There were no differences within the sequence encoding the II-III loop or the IS3/IS3-IS4 segment, excluding defects in these functional segments of the alpha 1 subunit as frequent causes of MH.

SUMMARY 1. Diltiazem (10 μmol/L) and verapamil (10 μmol/L) inhibited the hypercontractility induced by 3% halothane and 2 mmol/L caffeine in malignant hyperpyrexia susceptible (MHS) muscle. Diltiazem also inhibited 80 mmol/L KCl contractures. 2. Like the skeletal muscle relaxant dantrolene sodium (6 μmol/L), diltiazem not only prevented but reversed the abnormal contractures induced by halothane and caffeine. 3. The effect on caffeine contractures of diltiazem and dantrolene in combination was additive. 4. The ability of diltiazem and verapamil to inhibit the hypercontractility of MHS muscle suggests that Ca2+ influx across the transverse tubular membrane may be important in the aetiology of the malignant hyperpyrexia syndrome. 5. These results also suggest an abnormality in transverse tubule—sarcoplasmic reticulum communication.

The isoenzyme pattern and activity of adenylate kinase was studied in muscle and red blood cells from individuals and swine shown to be susceptible to malignant hyperpyraria. No abnormality in adenylate kinase isoenzyme pattern or activity was found.

1. The interactions between some drugs that contract and relax airways smooth muscle have been investigated in the cat isolated trachea. 2. Isoprenaline and theophylline inhibited serotonin-elicited contractions more than acetylcholine-mediated responses. This was observed both in terms of the degree of inhibition and the concentration of the relaxant drug producing this inhibition. 3. The acetylcholine- and serotonin-induced contractions were inhibited more by theophylline than by isoprenaline displaced acetylcholine and serotonin response curves to the right whereas theophylline caused a flattening of the curves. 4. Isoprenaline was more effective in hibiting serotonin contractions than acetylcholine contractions when the tracheas were bathed in K+ depolarizing solution, suggesting that the difference in the suscepbibility of serotonin and acetylcholine contractions to isoprenaline was not dependent on the electrical membrane potential. 5. Isoprenaline inhibited the tonic component of acetylcholine contractions more than the phasic component. 6. The differences in the pharmacological responses to the contractile and relaxant drugs in cat tracheal preparations provide further examples in smooth muscle of different mechanisms by which acetylcholine and serotonin induce contraction and isoprenaline and theophylline relaxation.

The contributions made by histamine, prostaglandins (PG) and slow reacting substances (SRS-A) to anaphylactic contractions in isolated guinea-pig lung were investigated. Histamine, PGF 2α and SRS-A induced isometric contractions in lung parenchymal strips and in tracheal smooth muscle. The effective concentrations of the autacoids were the same in lung strips and tracheas. Anaphylactic contractions in lung strips from bovine serum albumin sensitised animals were not affected by mepyramine (5 × 10 −6 M), or indomethacin (3 × 10 −5 M) but were markedly reduced by FPL 55712 (5 × 10 −5 M) suggesting that SRS-A plays a major role in the anaphylactic response. The effect of isoprenaline on anaphylactic histamine release and contractions was also examined. Anaphylactic contractions in lung strips were inhibited by isoprenaline (10 −10 – 10 −7 M). Isoprenaline also inhibited anaphylactic histamine release from lung parenchyma. 10 −7 M isoprenaline inhibited contractions by 85.6% and reduced histamine release by 27.9%. The results suggest that histmaine release does not contribute markedly to anaphylaxis in peripheral airways.

1. Contractile responses of guinea-pig tracheal smooth muscle to KCl, histamine, acetylcholine and prostaglandins were reduced after the removal of extracellular Ca2+ from the bathing medium. 2. KCl-induced contractures were more dependent on extracellular Ca2+ than acetylcholine-induced responses, but less so than histamine-induced contractures. 3. Responses to high concentrations of contractile agents were less dependent on extracellular Ca2+ than those to low concentrations. 4. Repeated additions of histamine or acetylcholine in the absence of extracellular Ca2+ resulted in progressively smaller contractile responses. 5. Treatment of tracheal muscle with EGTA considerably inhibited drug-induced contractures and abolished the response to KCl. 6. It is concluded that contractile responses of guinea-pig tracheal smooth muscle involve both the influx Ca2+ from the extracellular space and release of Ca2+ from intracellular sites. The relative contributions of these two Ca2+ sources depend on both the contractile agent and its concentration. Intracellular Ca2+ stores may be depleted by treatment with EGTA, or by repeated drug additions in the absence of extracellular calcium.

Skeletal muscle from normal human subjects produced linear contracture responses in vitro to caffeine at concentrations of between 4 and 32 mmol/litre. In the presence of 0.4% halothane, caffeine contractures were greater but the magnitude of halothane potentiation decreased as the caffeine concentration was increased. The contractures produced by caffeine 4 and 8 mmol/litre at 37 degrees C were significantly reduced by decreasing the temperature of the incubation solution to 25 degrees C. Among 57 normal subjects, 18% had fibres which responded to halothane treatment with contracture. On the basis of these findings, it is suggested that screening for malignant hyperpyrexia by in vitro pharmacological testing of skeletal muscle should be carried out at 37 degrees C, and should include exposure of the sample to halothane, caffeine, suxamethonium and potassium rather than to halothane alone.

1. 1. Malignant hyperpyrexia (MH) is an anaesthetic complication which is due to an underlying muscle membrane abnormality. 2. 2. One- and two-dimensional electrophoresis of skeletal muscle proteins were carried out to study the abnormality. 3. 3. No defect in MH susceptible muscle was found.

Histamine (10 −5 −3 × 10 −4 M) increased the cyclic AMP content of guinea-pig tracheal smooth muscle, the maximal effect being a 3-fold increase after 2 min incubation with 10 −4 M histamine. Histamine-induced accumulation of cyclic AMP was not affected by propanolol or atropine, but was reduced by mepyramine. Aspirin and indomethacin abolished the cyclic AMP response to histamine and potentiated histamine-induced contractions of the smooth muscle. These resuls suggest that the elevation of cyclic AMP levels in response to histamine is mediated by prostaglandins, and represents an important negative feedback regulatory mechanism which modulates the contractile response of guinea-pig tracheal smooth muscle to histamine.

SUMMARY 1. Imidazole contracted guinea-pig isolated tracheal smooth muscle, and at low concentrations (50 μnol/1 to 2 mmol/1) also enhanced contractions induced by histamine. 2. Imidazole had no effect on contractile responses to potassium chloride, acetylcholine, prostaglandin F2α, or the ionophore A23187; nor did it affect anaphylactic contractions in tracheal strips from guinea-pigs sensitized to ovalbumin. 3. Imidazole had no effect on the content of cyclic AMP in guinea-pig tracheal smooth muscle, nor did it affect the accumulation of cyclic AMP induced by histamine, isoprenaline, theophylline plus isoprenaline, or prostaglandin E1. 4. Imidazole-induced contractions were partially antagonized by atropine, mepyramine maleate and the omission of extracellular calcium ions. 5. Imidazole-induced hyperreactivity to histamine was not affected by atropine or indomethacin, and was more pronounced in the absence of extracellular calcium ions. 6. It is concluded that imidazole does not affect cyclic nucleotide phosphodiesterase activity in guinea-pig trachea, and its effects on contractile responses of the smooth muscle are unrelated to any action on cyclic AMP metabolism. The potentiating effect of imidazole may involve inhibition of histaminase, or the facilitation of calcium ion release from intracellular storage sites.

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

MH occurs in people who have a generalized membrane abnormality. Two clinical myopathies are known to be associated with this membrane defect. One is usually subclinical and is inherited as a mendelian dominant characteristic. The other occurs in boys who have a number of striking physical abnormalities, and is inherited as a recessive trait. When the abnormal muscle cell membrane is exposed to anesthetic agents such as halothane or succinylcholine there is a rapid, excessive release of calcium into the myoplasm. The raised myoplasmic calcium concentration leads to all the clinical features of the syndrome, predominant among which are: metabolic acidosis, a rise in body temperature, and rigidity--particularly in the muscles of the limbs. The exact site and nature of the lesion in the muscle cell membrane are still to be determined, but recent evidence suggests that it may lie in the E-C coupling mechanism. Understanding of the pathophysiology of MH has led to the development of an appropriate drug treatment for this syndrome, the aim of which is to restore the elevated myoplasmic calcium level to normal. Dantrolene sodium promises to be the most effective drug in achieving this result.

The effect of adenylate cyclase activation on the in vitro contractures of control and malignant hyperpyrexia susceptible (MHS) porcine muscle was investigated. While fluoride and molybdate ions potentiated drug-induced contractures in control muscle, other activators of adenylate cyclase (forskolin and noradrenaline) did not. Furthermore, fluoride and molybdate had no effect on MHS skeletal muscle contractility. Cyclic AMP content, basal adenylate cyclase activity and molybdate-stimulated adenylate cyclase activity of MHS skeletal muscle was not significantly different from that of control muscle. It is concluded that increased activity of adenylate cyclase does not represent the primary skeletal muscle defect which predisposes to porcine MH.

31Phosphorus-NMR spectroscopy may have the potential to help in the noninvasive diagnosis of malignant hyperpyrexia (MH). Changes in the phosphate-metabolite profile of MH-susceptible (MHS) skeletal muscle occur more readily under conditions of anoxia than in control muscle. Induction of anoxia caused a rapid fall in intracellular phosphocreatine, an elevation of inorganic phosphate, and finally a diminution of ATP in MHS muscle. The onset of metabolic change was slower in control tissue. Increased oxygen consumption may occur in anoxic MHS muscle, which leads to accelerated glycolysis and a rapid fall in the intracellular high-energy phosphates. In MHS muscle an abnormality may exist in carbohydrate metabolism linked with poor resynthesis of the high-energy phosphates, which may be precipitated under anaerobic conditions. Accelerated muscle metabolism is also observed in the presence of 2 mM caffeine and 3% halothane in MHS muscle. Changes in the concentrations of metabolites could be mapped noninvasively under anoxic conditions using topical 31P-NMR.

In both control pigs and pigs susceptible to malignant hyperpyrexia (MH), the size of the calcium current (ICa) and the amount of asymmetric charge movement varied considerably between different gracilis muscle fibers but appeared to vary in parallel. The mean amount of both ICa and charge movement were slightly but significantly smaller in MH-susceptible (MHS) muscle compared with normal muscle. Halothane (1% v/v) reduced both parameters by almost 50%. One interpretation of the data is that the signal, which couples depolarization to calcium release from the sarcoplasmic reticulum, is abnormal in MHS muscle.

SUMMARY The effects of i.v. and local anaesthetics on guineapig tracheal smooth muscle have been investigated in vitro. Diazepam, propanidid and ketamine induced relaxation and antagonized histamine-, acetylcholine- and potassium chloride-induced contractures in the tracheal smooth muscle. The relaxing effects of the anaesthetics were not affected by propranoioi. Thiopentone, at concentrations which would be used clinically, caused contracture of the tracheal smooth muscle. Morphine induced relaxation and antagonized histamine-induced contracture, but did not antagonize acetyicholine- or potassium chloride-induced contractures. Lignocaine and procaine, at clinical concentrations, induced contracture of tracheal smooth muscle. Large doses of lignocaine relaxed the tracheal muscle, but large doses of procaine induced spontaneous rhythmical movements. Lignocaine and procaine antagonized contractures induced by histamine, acetylcholine and potassium chloride.

1. 1. The anaesthetic complication malignant hyperpyrexia (MH) is due to an elevation myoplasmic Ca2+ concentration. 2. 2. Examination of calmodulin isolated from MH susceptible swine suggests that the disorder in calcium regulation in MH is not due to an abnormality in calmodulin.

The sarcoplasmic reticulum from muscle of swine which are susceptible to malignant hyperpyrexia is deficient in inositol 1,4,5-trisphosphate phosphatase (InsP35-ase) activity, which leads to high intracellular concentrations of inositol 1,4,5-trisphosphate (InsP3) and of calcium ions. Halothane inhibits InsP35-ase and further increases myoplasmic InsP3 and calcium ion concentrations, and produces the clinical features of malignant hyperpyrexia.

1. The effects of dantrolene on pharmacologically-induced contractures and potentiated isometric twitches in normal human skeletal muscle have been studied in vitro. 2. Dantrolene sodium, at concentrations of 3 mumol/l or less, attenuates basal twitch, inhibits halothane potentiation of basal twitch and inhibits halothane-potentiated potassium contractures, but has less effect on twitch potentiation by 2 mmol/l caffeine. 3. Caffeine contractures are attenuated by dantrolene concentrations of 12 mumol/l or greater. The effect of dantrolene on caffeine contracture is characterized by decreased contracture tension and by prolonged time to peak contracture. 4. The results indicate that halothane and 2 mmol/l caffeine have agonistic effects on the excitation-contraction (E-C) coupling mechanism, and suggest that they may act at separate E-C coupling sites. The relationships of these findings to the pathopharmacology of malignant hyperpyrexia are discussed.

Contractures induced by halothane, caffeine, suxamethonium chloride and potassium in malignant hyperpyrexia-susceptible (MHS) and control swine skeletal muscle preparations were temperature-dependent, but differed in their temperature response profiles. Increasing the temperatures from 20 degrees C to 37 degrees C increased drug-induced contractures in MHS muscle. At 5 degrees C drug-induced contractures were not inhibited by dantrolene sodium, deuterium oxide or glycerination in either MHS or control muscle. These observations give further support to the view that the abnormality in MHS skeletal muscle is associated with the mechanism of excitation-contraction coupling.

1. Landrace swine were identified as malignant hyperpyrexia susceptible (MHS) or control by the contracture responses of gracilis muscle fibre bundles to 3% halothane, 2 mmol/l caffeine and 80 mmol/l KCl. The effects of calmodulin-antagonist drugs on the contractile behaviour of control and MHS preparations were investigated in vitro. 2. Calmodulin-antagonists at micromolar concentrations induced contracture in both control and MHS muscle. Pretreatment of MHS muscle with calmodulin-antagonist drugs potentiated its response to halothane and caffeine. 3. These results suggest that calmodulin-antagonist drugs cause an increase in myoplasmic Ca2+ concentration in both control and MHS muscle.

1. 1. The anaesthetic complication malignant hyperpyrexia (MH) occurs in individuals and swine with a muscle membrane abnormality. 2. 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. 3. No significant abnormality in the membrane protein or lipid content of MH-susoeptible muscle was detected.

The caffeine contracture of normal human muscle, which has been used as a model for malignant hyperpyrexia, is greatly potentiated by halothane. Prior administration of procaine markedly reduces the halothane-potentiated caffeine contracture, and procaine given at the height of the contracture induces relaxation. Lignocaine, on the other hand, produces a variable response and sometimes increases the contracture.The muscle from a patient with an inherited susceptibility to malignant hyperpyrexia contracted spontaneously with halothane alone, and this contracture was reversed by procaine.These experiments support the therapeutic use of procaine in malignant hyperpyrexia.

Malignant hyperthermia (hyperpyrexia) (MH) was first described in 19601 in dramatic circumstances, when an injured 21-year-old man nearly died following anesthesia with halothane. He had given a history that 10 of his close relatives had died as a result of anesthesia with ether. Since then, MH has come to be recognized as an important cause of anesthetic induced death, and has been the subject of extensive investigation.

Adenylate kinase has been implicated as a key factor in malignant hyperpyrexia, a complication of general anaesthesia which is usually triggered by the anaesthetic drug, halothane. Because of this, the enzyme was purified from both malignant hyperpyrexia susceptible and control porcine muscle. Electrophoretic studies, amino acid analysis, and peptide mapping of the purified enzymes revealed no significant differences between the two preparations. Both enzymes responded similarly to halothane and to the three sulfhydryl reacting reagents which were tested and they also showed an identical affinity for the substrate AMP. It is concluded that porcine MH is not due to an abnormality in the enzyme AK.

The mechanisms involved in the anti-asthmatic action of combined bronchodilator therapy was studied by determining the effects of combined salbutamol and theophylline on anaphylactic contractions, histamine release, prostaglandin (PG)F2 ALha release, cyclic 3',5'-adenosine monophosphate (c-AMP) and smooth muscle tone in guinea-pig peripheral airways in vitro. Combined, salbutamol (3 X 10(=8) M) and theophylline (3 X 10(-4) M) markedly inhibited anaphylactic contractions (85.8%) in lung strips. The inhibition of anaphylactic contractions was significantly greater than inhibition of histamine and PGF2 alpha-induced contractions. Histamine release was reduced by 66.1% but PGF2 alpha was not significantly altered. Increased c-AMP was observed with combined salbutamol (3 X 10(-8) M) and theophylline (3 X 10(-4) M) in the absence of antigen. The combined effect of salbutamol and theophylline was always greater than the sum of their individual effects. The results demonstrate that in peripheral airways theophylline potentiates the action of salbutamol both directly via smooth muscle relaxation and indirectly via inhibition in mediator release.

SUMMARY 1. The effects of caffeine, halothane, potassium chloride and procaine have been studied on normal human skeletal muscle in vitro. Particular emphasis has been given to the role played by extracellular calcium ions in producing these effects. 2. Caffeine produces a concentration-dependent contracture probably by stimulating the release of calcium ions from the calcium storing membranes of the muscle cell. 3. Halothane potentiates the contractures produced by caffeine and potassium chloride probably by facilitating the release of calcium from the storage membranes. 4. Potassium chloride produces a contracture only in the presence of caffeine or halothane. 5. Procaine inhibits all the contractures studied.

Of the various drugs currently suggested for the treatment of malignant hyperpyrexia, dantrolene sodium was the most effective in reversing and inhibiting drug induced contractures in vitro, both in normal muscle and in muscle from patients who are susceptible to malignant hyperpyrexia. It is suggested that dantrolene sodium is the drug of choice for lowering the raised myoplasmic calcium concentrations in malignant hyperpyrexia.

Summary: An interaction of bile with erythromycin lactobionate in vitro has been demonstrated. The major bile components involved in this interaction have been shown to be the bile salts. The nature of the bile salt-erythromycin interaction has been investigated. The way in which an interaction between bile salts and erythromycin in vivo might lead to the hepatic dysfunction and cholestasis associated with some instances of erythromycin therapy is discussed.