A case of discordance between genotype and phenotype in a malignant hyperthermia family.
(17/1763)
Malignant hyperthermia (MH) is an inherited autosomal dominant pharmacogenetic disorder and is the major cause of anaesthesia-induced death. Malignant hyperthermia susceptibility is usually diagnosed by the in vitro contracture test (IVCT) performed on fresh muscle biopsies exposed to caffeine and halothane, respectively. Around 50% of affected families are linked to the ryanodine receptor (RYR1) gene. The human RYR1 gene maps to chromosome 19q13.1 and encodes a protein that associates as a homotetramer and acts as a calcium-release channel from the sarcoplasmic reticulum. To date, 17 mutations have been identified in the coding region of the RYR1 gene and appear to be associated to the MH-susceptible phenotype. Here we describe a rare case of discordance between genotype (characterised by the presence of the Arg614Cys mutation in the RYR1 gene) and MH-normal typed phenotype. Although the IVCT remains a very reliable procedure for the assessment of MH status, genetic data can provide in some cases an additional aid to clinical diagnosis. (+info)
Effects of halothane and isoflurane on fast and slow inactivation of human heart hH1a sodium channels.
(18/1763)
BACKGROUND: Cloning and heterologous expression of ion channels allow biophysical and molecular studies of the mechanisms of volatile anesthetic interactions with human heart sodium channels. Volatile anesthetics may influence the development of arrhythmias arising from cardiac sodium channel dysfunction. For that reason, understanding the mechanisms of interactions between these anesthetics and cardiac sodium channels is important. This study evaluated the mechanisms of volatile anesthetic actions on the cloned human cardiac sodium channel (hH1a) alpha subunit. METHODS: Inward sodium currents were recorded from human embryonic kidney (HEK293) cells stably expressing hH1a channels. The effects of halothane and isoflurane on current and channel properties were evaluated using the whole cell voltage-clamp technique. RESULTS: Halothane at 0.47 and 1.1 mM and isoflurane at 0.54 and 1.13 mM suppressed the sodium current in a dose- and voltage-dependent manner. Steady state activation was not affected, but current decay was accelerated. The voltage dependence of steady state fast and slow inactivations was shifted toward more hyperpolarized potentials. The slope factor of slow but not fast inactivation curves was reduced significantly. Halothane increased the time constant of recovery from fast inactivation. The recovery from slow inactivation was not affected significantly by either anesthetic. CONCLUSIONS: In a heterologous expression system, halothane and isoflurane interact with the hH1a channels and suppress the sodium current. The mechanisms involve acceleration of the transition from the open to the inactivated state, stabilization of the fast and slow inactivated states, and prolongation of the inactivated state by delayed recovery from the fast inactivated to the resting state. (+info)
Halothane presynaptically depresses synaptic transmission in wild-type Drosophila larvae but not in halothane-resistant (har) mutants.
(19/1763)
BACKGROUND: General anesthetics produce important changes in neural function, but the relation between the many individual changes produced by anesthetics in neural components and the responsiveness of the whole organism is uncertain. An analysis of genetically altered animals that have modified responses to volatile anesthetics may help to allay this uncertainty. METHODS: The authors evaluated the effect of halothane on synaptic transmission at the larval neuromuscular junction in wild-type (Ore-R) and halothane-resistant (har) mutants of Drosophila melanogaster. The body wall muscles, which are innervated by glutamatergic nerves, were voltage clamped at -60 mV using the patch-clamp technique in the whole cell configuration. Nerve-evoked excitatory junctional currents and miniature excitatory junctional currents were recorded. The effects of halothane on the amplitude of these currents were compared in Ore-R and two bar mutants derived from the Ore-R strain. The time course and frequency of miniature excitatory junctional currents also were analyzed in the presence of halothane. RESULTS: In Ore-R, halothane (1.8%; 1.01 mM) significantly reduced the amplitude of nerve-evoked excitatory junctional currents (61.9+/-17% of control, mean +/- SD; n = 7), but not that of miniature excitatory junctional currents. Conversely, in two har mutants, halothane had no effect on the amplitude of either nerve-evoked excitatory junctional currents or miniature excitatory junctional currents. In Ore-R, the frequency of miniature excitatory junctional currents was decreased significantly in the presence of halothane (0.9-2.7%; 0.52-1.46 mM), whereas halothane did not change the frequency in two har mutants. The miniature excitatory junctional current decay time constant, thought to reflect the kinetic properties of junctional glutamate receptor channels, was not changed by halothane in either the Ore-R strain or the har mutants. CONCLUSIONS: Halothane depresses synaptic transmission at the wild-type Drosophila neuromuscular junction, most likely by affecting presynaptic properties. The absence of an effect by halothane in the har mutants provides evidence that the depression of presynaptic function at the glutamate-mediated synapses is an important contributor to the way halothane alters the responsiveness of the whole animal. (+info)
Halothane enhances exocytosis of [3H]-acetylcholine without increasing calcium influx in rat brain cortical slices.
(20/1763)
1. The effect of halothane on the release of [3H]-acetylcholine ([3H]-ACh) in rat brain cortical slices was investigated. 2. Halothane (0.018 mM) did not significantly affect the basal and the electrical field stimulation induced release of [3H]-ACh. However, halothane (0.063 mM) significantly increased the basal release of [3H]-ACh and this effect was additive with the electrical field stimulation induced release of [3H]-ACh. 3. The release of [3H]-ACh induced by 0.063 mM halothane was independent of the extracellular sodium and calcium ion concentration and was decreased by tetracaine, an inhibitor of Ca(2+)-release from intracellular stores or dantrolene, an inhibitor of Ca(2+)-release from ryanodine-sensitive stores 4. Using 2-(4-phenylpiperidino)-cyclohexanol (vesamicol), a drug that blocks the storage of ACh in synaptic vesicles, we investigated whether exocytosis of this neurotransmitter is involved in the effect of halothane. Vesamicol significantly decreased the release of [3H]-ACh evoked by halothane. 5. It is suggested that halothane may cause a Ca2+ release from intracellular stores that increases [3H]-ACh exocytosis in rat brain cortical slices. (+info)
Bactericidal activity of rat lung lavage fluid against Bordetella pertussis.
(21/1763)
Cell-free lung lavage fluid (LLF) from healthy normal rats killed phase I (wild-type, virulent) Bordetella pertussis at 37 degrees C in vitro. B. parapertussis was also killed by the LLF, but phase IV (avirulent mutant) B. pertussis and some other common bacterial species, including B. bronchiseptica, were not. Transmission electron microscopy of thin sections of the phase I B. pertussis showed extensive structural damage and cell lysis. None of the other mammalian species tested had LLF with bactericidal activity against B. pertussis as high as that of the rat. Rats killed with halothane yielded LLF with higher bactericidal activity than when CO2 was used. Ultracentrifugation of LLF at 55,000 g gave a surfactant (pellet) fraction that had c. 95% of the bactericidal activity and which was biochemically distinct from the 5% of activity in the supernate fraction. Phospholipids and fatty acids appeared to be involved in LLF bactericidal activity, but not complement or lysozyme. Arachidonic acid was the most active of the fatty acids tested. Artificial surfactant, as used in premature infants, had no bactericidal effect on B. pertussis. (+info)
Differential effects of sevoflurane, isoflurane, and halothane on Ca2+ release from the sarcoplasmic reticulum of skeletal muscle.
(22/1763)
BACKGROUND: Although malignant hyperthermia after application of sevoflurane has been reported, little is known about its action on intracellular calcium homeostasis of skeletal muscle. The authors compared the effect of sevoflurane with that of isoflurane and halothane on Ca2+ release of mammalian sarcoplasmic reticulum and applied a novel method to quantify Ca2+ turnover in permeabilized skeletal muscle fibers. METHODS: Liquid sevoflurane, isoflurane, and halothane at 0.6 mM, 3.5 mM, and 7.6 mm were diluted either in weakly calcium buffered solutions with no added Ca2+ (to monitor Ca2+ release) or in strongly Ca2+ buffered solutions with [Ca2+] values between 3 nM and 24.9 microm for [Ca+]-force relations. Measurements were taken on single saponin skinned muscle fiber preparations of BALB/c mice. Individual [Ca2+]force relations were characterized by the Ca2+ concentration at half-maximal force that indicates the sensitivity of the contractile proteins and by the steepness. Each force transient was transformed directly into a Ca2+ transient with respect to the individual [Ca2+]-force relation of the fiber. RESULTS: At 0.6 mM, single force transients induced by sevoflurane were lower compared with equimolar concentrations of isoflurane and halothane (P < 0.05). Similarly, calculated peak Ca2+ transients of sevoflurane were lower than those induced by equimolar halothane (P < 0.05). The Ca2+ concentrations at half maximal force were decreased after the addition of sevoflurane, isoflurane, and halothane in a concentration-dependent manner (P < 0.05). CONCLUSION: Whereas sevoflurane, isoflurane, and halothane similarly increase the Ca2+ sensitivity of the contractile apparatus in skeletal muscle fibers, 0.6 mM sevoflurane induces smaller Ca2+ releases from the sarcoplasmic reticulum than does equimolar halothane. (+info)
Molecular dynamics simulation of a synthetic four-alpha-helix bundle that binds the anesthetic halothane.
(23/1763)
The structural features of binding sites for volatile anesthetics are examined by performing a molecular dynamics simulation study of the synthetic four-alpha-helix bundles (Aalpha2)2, which are formed by association of two 62-residue di-alpha-helical peptides. The peptide bundle (Aalpha2)2 was designed by Johansson et al. [Biochemistry 37 (1998) 1421-1429] and was shown experimentally to have a high affinity for the binding of the anesthetic halothane (CF3CBrCIH) in a hydrophobic cavity. Since (Aalpha2)2 can exhibit either the anti or syn topologies, the two distinct bundles are simulated both in the presence and in the absence of halothane. Nanosecond length molecular dynamics trajectories were generated for each system at room temperature (T = 298 K). The structural and dynamic effects of the inclusion of halothane are compared, illustrating that the structures are stable over the course of the simulation; that the (Aalpha2)2 bundles have suitable pockets that can accommodate halothane; that the halothane remains in the designed hydrophobic cavity in close proximity to the Trp residues with a preferred orientation; and that the dimensions of the peptide are perturbed by the inclusion of an anesthetic molecule. (+info)
Specific actions of halothane, isoflurane, and desflurane on sympathetic activity and A delta and C somatosympathetic reflexes recorded in renal nerves in dogs.
(24/1763)
BACKGROUND: This was a study of the relative effects on directly recorded sympathetic activity of desflurane, isoflurane, and halothane. METHODS: Renal sympathetic nerve activity (RSNA) was recorded with bipolar electrodes in renal nerves exposed retroperitoneally in anesthetized (alpha-chloralose), paralyzed (succinylcholine), and artificially ventilated dogs. Somatosympathetic responses were evoked by supramaximal electrical stimulation of radial nerves (0.33 Hz, 30 V, 0.5 ms). Spontaneous and evoked activity were rectified, averaged, and integrated to allow quantitative comparison of the effects of 3-12% desflurane, 0.6-2.4% isoflurane, and 0.4-1.6% halothane. RESULTS: Increasing concentrations of isoflurane progressively depressed mean RSNA, Adelta, and C reflexes by 40% (P < 0.01), 50% (P < 0.01) and 70% (P < 0.001) respectively at 2.4% concentration. Halothane depressed both reflexes equally by approximately 60% (P < 0.01) at 1.6% concentration, without significant depression of spontaneous RSNA. Desflurane increased and subsequently decreased RSNA by 37% (P < 0.02) and 65% (P < 0.001) at concentrations of 6% and 12% respectively, and although somatosympathetic reflexes remained unchanged up to 9%, both were depressed equally by 70% (P < 0.01) at 12% concentration. CONCLUSION: After equilibration, lower concentrations of desflurane remained excitatory, but, like isoflurane, higher concentrations depressed RSNA. The effect of halothane on RSNA was insignificant. Isoflurane depressed C more than Adelta somatosympathetic reflexes, which is uncorrelated with lipid solubility because desflurane and halothane, which have the highest and lowest minimum alveolar concentration, respectively, depressed both equally. (+info)