Voltage modulates halothane-triggered Ca2+ release in malignant hyperthermia-susceptible muscle

Сhanges of trace elements in the cerebellum and their influence on the rats behavior in elevated plus maze in the acute period of mild blast-induced brain injury

BACKGROUND

In connection with the widespread use of explosive devices in military conflicts, in particular in Ukraine, is relevant to detect the biometals changes in the cerebellum and determine the presence of their influence on the behavior changes of rats in the elevated plus maze in the acute period of a mild blast-traumatic brain injury (bTBI).

METHODS

The selected rats were randomly divided into 3 groups: Group I - Experimental with bTBI (with an excess pressure of 26-36 kPa), Group II - Sham and Group III - Intact. Behavior studies was in the elevated plus maze. Brain spectral analysis was with using of energy dispersive X-ray fluorescence analysis, after obtaining the quantitative mass fractions of biometals, the ratios of Cu/Fe, Cu/Zn, Zn/Fe were calculated and the data between the three groups were compared.

RESULTS

The results showed an increase in mobility in the experimental rats, which indicates functional disorders of the cerebellum in the form of maladaptation in space. Changes in cognitive activity also is an evidence of cerebellum suppression, which is indicated by changes in vertical locomotor activity. Grooming time was shortened. We established a significant increase in Cu/Fe and Zn/Fe ratios in the cerebellum, a decrease in Cu/Zn.

CONCLUSIONS

Changes in the Cu/Fe, Cu/Zn, and Zn/Fe ratios in the cerebellum correlate with impaired locomotor and cognitive activity in rats in the acute posttraumatic period. Accumulation of Fe on the 1st and 3rd day leads to disturbance of the Cu and Zn balance on the 7th day and starts a "vicious cycle" of neuronal damage. Cu/Fe, Cu/Zn, and Zn/Fe imbalances are secondary factors in the pathogenesis of brain damage as a result of primary bTBI.

Distinct pathophysiological characteristics in developing muscle from patients susceptible to malignant hyperthermia

BACKGROUND

Most patients with malignant hyperthermia susceptibility diagnosed by the in vitro caffeine-halothane contracture test (CHCT) develop excessive force in response to halothane but not caffeine (halothane-hypersensitive). Hallmarks of halothane-hypersensitive patients include high incidence of musculoskeletal symptoms at rest and abnormal calcium events in muscle. By measuring sensitivity to halothane of myotubes and extending clinical observations and cell-level studies to a large group of patients, we reach new insights into the pathological mechanism of malignant hyperthermia susceptibility.

METHODS

Patients with malignant hyperthermia susceptibility were classified into subgroups HH and HS (positive to halothane only and positive to both caffeine and halothane). The effects on [Ca2+]cyto of halothane concentrations between 0.5 and 3 % were measured in myotubes and compared with CHCT responses of muscle. A clinical index that summarises patient symptoms was determined for 67 patients, together with a calcium index summarising resting [Ca2+]cyto and spontaneous and electrically evoked Ca2+ events in their primary myotubes.

RESULTS

Halothane-hypersensitive myotubes showed a higher response to halothane 0.5% than the caffeine-halothane hypersensitive myotubes (P<0.001), but a lower response to higher concentrations, comparable with that used in the CHCT (P=0.055). The HH group had a higher calcium index (P<0.001), but their clinical index was not significantly elevated vs the HS. Principal component analysis identified electrically evoked Ca2+ spikes and resting [Ca2+]cyto as the strongest variables for separation of subgroups.

CONCLUSIONS

Enhanced sensitivity to depolarisation and to halothane appear to be the primary, mutually reinforcing and phenotype-defining defects of halothane-hypersensitive patients with malignant hyperthermia susceptibility.

Anesthetics and Cell-Cell Communication: Potential Ca2+-Calmodulin Role in Gap Junction Channel Gating by Heptanol, Halothane and Isoflurane

Cell–cell communication via gap junction channels is known to be inhibited by the anesthetics heptanol, halothane and isoflurane; however, despite numerous studies, the mechanism of gap junction channel gating by anesthetics is still poorly understood. In the early nineties, we reported that gating by anesthetics is strongly potentiated by caffeine and theophylline and inhibited by 4-Aminopyridine. Neither Ca²⁺ channel blockers nor 3-isobutyl-1-methylxanthine (IBMX), forskolin, CPT-cAMP, 8Br-cGMP, adenosine, phorbol ester or H7 had significant effects on gating by anesthetics. In our publication, we concluded that neither cytosolic Ca²⁺_i nor pH_i were involved, and suggested a direct effect of anesthetics on gap junction channel proteins. However, while a direct effect cannot be excluded, based on the potentiating effect of caffeine and theophylline added to anesthetics and data published over the past three decades, we are now reconsidering our earlier interpretation and propose an alternative hypothesis that uncoupling by heptanol, halothane and isoflurane may actually result from a rise in cytosolic Ca²⁺ concentration ([Ca²⁺]_i) and consequential activation of calmodulin linked to gap junction proteins.

Heat-hypersensitive mutants of ryanodine receptor type 1 revealed by microscopic heating

Malignant hyperthermia (MH) is a life-threatening disorder caused largely by mutations in ryanodine receptor type 1 (RyR1) Ca²⁺-release channels. Enhanced Ca²⁺ release through the mutant channels induces excessive heat development upon exposure to volatile anesthetics. However, the mechanism by which Ca²⁺ release is accelerated at an elevated temperature is yet to be identified. Fluorescence Ca²⁺ imaging with rapid heating by an infrared laser beam provides direct evidence that heat induces Ca²⁺ release through the RyR1 channel. And the mutant channels are more heat sensitive than the wild-type channels, thereby causing an increase in the cytosolic Ca²⁺ concentration in mutant cells. It is likely that the heat-induced Ca²⁺ release participates as an enhancer in the cellular mechanism of MH.

Thermoregulation is an important aspect of human homeostasis, and high temperatures pose serious stresses for the body. Malignant hyperthermia (MH) is a life-threatening disorder in which body temperature can rise to a lethal level. Here we employ an optically controlled local heat-pulse method to manipulate the temperature in cells with a precision of less than 1 °C and find that the mutants of ryanodine receptor type 1 (RyR1), a key Ca²⁺ release channel underlying MH, are heat hypersensitive compared with the wild type (WT). We show that the local heat pulses induce an intracellular Ca²⁺ burst in human embryonic kidney 293 cells overexpressing WT RyR1 and some RyR1 mutants related to MH. Fluorescence Ca²⁺ imaging using the endoplasmic reticulum–targeted fluorescent probes demonstrates that the Ca²⁺ burst originates from heat-induced Ca²⁺ release (HICR) through RyR1-mutant channels because of the channels’ heat hypersensitivity. Furthermore, the variation in the heat hypersensitivity of four RyR1 mutants highlights the complexity of MH. HICR likewise occurs in skeletal muscles of MH model mice. We propose that HICR contributes an additional positive feedback to accelerate thermogenesis in patients with MH.

T lymphocytes from malignant hyperthermia-susceptible mice display aberrations in intracellular calcium signaling and mitochondrial function

Gain-of-function RyR1-p.R163C mutation in ryanodine receptors type 1 (RyR1) deregulates Ca²⁺ signaling and mitochondrial function in skeletal muscle and causes malignant hyperthermia in humans and mice under triggering conditions. We investigated whether T lymphocytes from heterozygous RyR1-p.R163C knock-in mutant mice (HET T cells) display measurable aberrations in resting cytosolic Ca²⁺ concentration ([Ca²⁺]_i), Ca²⁺ release from the store, store-operated Ca²⁺ entry (SOCE), and mitochondrial inner membrane potential (ΔΨ_m) compared with T lymphocytes from wild-type mice (WT T cells). We explored whether these variables can be used to distinguish between T cells with normal and altered RyR1 genotype. HET and WT T cells were isolated from spleen and lymph nodes and activated in vitro using phytohemagglutinin P. [Ca²⁺]_i and ΔΨ_m dynamics were examined using Fura 2 and tetramethylrhodamine methyl ester fluorescent dyes, respectively. Activated HET T cells displayed elevated resting [Ca²⁺]_i, diminished responses to Ca²⁺ mobilization with thapsigargin, and decreased rate of [Ca²⁺]_i elevation in response to SOCE compared with WT T cells. Pretreatment of HET T cells with ryanodine or dantrolene sodium reduced disparities in the resting [Ca²⁺]_i and ability of thapsigargin to mobilize Ca²⁺ between HET and WT T cells. While SOCE elicited dissipation of the ΔΨ_m in WT T cells, it produced ΔΨ_m hyperpolarization in HET T cells. When used as the classification variable, the amplitude of thapsigargin-induced Ca²⁺ transient showed the best promise in predicting the presence of RyR1-p.R163C mutation. Other significant variables identified by machine learning analysis were the ratio of resting cytosolic Ca²⁺ level to the amplitude of thapsigargin-induced Ca²⁺ transient and an integral of changes in ΔΨ_m in response to SOCE. Our study demonstrated that gain-of-function mutation in RyR1 significantly affects Ca²⁺ signaling and mitochondrial fiction in T lymphocytes, which suggests that this mutation may cause altered immune responses in its carrier. Our data link the RyR1-p.R163C mutation, which causes inherited skeletal muscle diseases, to deregulation of Ca²⁺ signaling and mitochondrial function in immune T cells and establish proof-of-principle for in vitro T cell-based diagnostic assay for hereditary RyR1 hyperfunction.

Preclinical model systems of ryanodine receptor 1-related myopathies and malignant hyperthermia: a comprehensive scoping review of works published 1990-2019

BACKGROUND

Pathogenic variations in the gene encoding the skeletal muscle ryanodine receptor (RyR1) are associated with malignant hyperthermia (MH) susceptibility, a life-threatening hypermetabolic condition and RYR1-related myopathies (RYR1-RM), a spectrum of rare neuromuscular disorders. In RYR1-RM, intracellular calcium dysregulation, post-translational modifications, and decreased protein expression lead to a heterogenous clinical presentation including proximal muscle weakness, contractures, scoliosis, respiratory insufficiency, and ophthalmoplegia. Preclinical model systems of RYR1-RM and MH have been developed to better understand underlying pathomechanisms and test potential therapeutics.

METHODS

We conducted a comprehensive scoping review of scientific literature pertaining to RYR1-RM and MH preclinical model systems in accordance with the PRISMA Scoping Reviews Checklist and the framework proposed by Arksey and O'Malley. Two major electronic databases (PubMed and EMBASE) were searched without language restriction for articles and abstracts published between January 1, 1990 and July 3, 2019.

RESULTS

Our search yielded 5049 publications from which 262 were included in this review. A majority of variants tested in RYR1 preclinical models were localized to established MH/central core disease (MH/CCD) hot spots. A total of 250 unique RYR1 variations were reported in human/rodent/porcine models with 95% being missense substitutions. The most frequently reported RYR1 variant was R614C/R615C (human/porcine total n = 39), followed by Y523S/Y524S (rabbit/mouse total n = 30), I4898T/I4897T/I4895T (human/rabbit/mouse total n = 20), and R163C/R165C (human/mouse total n = 18). The dyspedic mouse was utilized by 47% of publications in the rodent category and its RyR1-null (1B5) myotubes were transfected in 23% of publications in the cellular model category. In studies of transfected HEK-293 cells, 57% of RYR1 variations affected the RyR1 channel and activation core domain. A total of 15 RYR1 mutant mouse strains were identified of which ten were heterozygous, three were compound heterozygous, and a further two were knockout. Porcine, avian, zebrafish, C. elegans, canine, equine, and drosophila model systems were also reported.

CONCLUSIONS

Over the past 30 years, there were 262 publications on MH and RYR1-RM preclinical model systems featuring more than 200 unique RYR1 variations tested in a broad range of species. Findings from these studies have set the foundation for therapeutic development for MH and RYR1-RM.

Excessive Accumulation of Ca2 + in Mitochondria of Y522S-RYR1 Knock-in Mice: A Link Between Leak From the Sarcoplasmic Reticulum and Altered Redox State

Mice (Y522S or YS), carrying a mutation of the sarcoplasmic reticulum (SR) Ca2+ release channel of skeletal muscle fibers (ryanodine receptor type-1, RyR1) which causes Ca2+ leak, are a widely accepted and intensively studied model for human malignant hyperthermia (MH) susceptibility. Since the involvement of reactive oxygen species (ROS) and of mitochondria in MH crisis has been previously debated, here we sought to determine Ca2+ uptake in mitochondria and its possible link with ROS production in single fibers isolated from flexor digitorum brevis (FDB) of YS mice. We found that Ca2+ concentration in the mitochondrial matrix, as detected with the ratiometric FRET-based 4mtD3cpv probe, was higher in YS than in wild-type (WT) fibers at rest and after Ca2+ release from SR during repetitive electrical stimulation or caffeine administration. Also mitochondrial ROS production associated with contractile activity (detected with Mitosox probe) was much higher in YS fibers than in WT. Importantly, the inhibition of mitochondrial Ca2+ uptake achieved by silencing MCU reduced ROS accumulation in the matrix and Ca2+ release from SR. Finally, inhibition of mitochondrial ROS accumulation using Mitotempo reduced SR Ca2+ release in YS fibers exposed to caffeine. The present results support the view that mitochondria take up larger amounts of Ca2+ in YS than in WT fibers and that mitochondrial ROS production substantially contributes to the increased caffeine-sensitivity and to the enhanced Ca2+ release from SR in YS fibers.

Abnormal calcium signalling and the caffeine-halothane contracture test

BACKGROUND

The variable clinical presentation of malignant hyperthermia (MH), a disorder of calcium signalling, hinders its diagnosis and management. Diagnosis relies on the caffeine-halothane contracture test, measuring contraction forces upon exposure of muscle to caffeine or halothane (FC and FH, respectively). Patients with above-threshold FC or FH are diagnosed as MH susceptible. Many patients test positive to halothane only (termed 'HH'). Our objective was to determine the characteristics of these HH patients, including their clinical symptoms and features of cytosolic Ca2+ signalling related to excitation-contraction coupling in myotubes.

METHODS

After institutional ethics committee approval, recruited patients undergoing contracture testing at Toronto's MH centre were assigned to three groups: HH, doubly positive (HS), and negative patients (HN). A clinical index was assembled from musculoskeletal symptoms and signs. An analogous calcium index summarised four measures in cultured myotubes: resting [Ca2+]cytosol, frequency of spontaneous cytosolic Ca2+ events, Ca2+ waves, and cell-wide Ca2+ spikes after electrical stimulation.

RESULTS

The highest values of both indexes were found in the HH group; the differences in calcium index between HH and the other groups were statistically significant. The principal component analysis confirmed the unique cell-level features of the HH group, and identified elevated resting [Ca2+]cytosol and spontaneous event frequency as the defining HH characteristics.

CONCLUSIONS

These findings suggest that HH pathogenesis stems from excess Ca2+ leak through sarcoplasmic reticulum channels. This identifies HH as a separate diagnostic group and opens their condition to treatment based on understanding of pathophysiological mechanisms.