Ryanodine receptor activity and store-operated Ca2+ entry: Critical regulators of Ca2+ content and function in skeletal muscle

Store-operated Ca2+ entry (SOCE) is critical to cell function. In skeletal muscle, SOCE has evolved alongside excitation-contraction coupling (EC coupling); as a result, it displays unique properties compared to SOCE in other cells. The plasma membrane of skeletal muscle is mostly internalized as the tubular system, with the tubules meeting the sarcoplasmic reticulum (SR) terminal cisternae, forming junctions where the proteins that regulate EC coupling and SOCE are positioned. In this review, we describe the properties and roles of SOCE based on direct measurements of Ca2+ influx during SR Ca2+ release and leak. SOCE is activated immediately and locally as the [Ca2+ ] of the junctional SR terminal cisternae ([Ca2+ ]jSR ) depletes. [Ca2+ ]jSR changes rapidly and steeply with increasing activity of the SR ryanodine receptor isoform 1 (RyR1). The high fidelity of [Ca2+ ]jSR with RyR1 activity probably depends on the SR Ca2+ -buffer calsequestrin that is located immediately behind RyR1 inside the SR. This arrangement provides in-phase activation and deactivation of SOCE with a large dynamic range, allowing precise grading of SOCE flux. The in-phase activation of SOCE as the SR partially depletes traps Ca2+ in the cytoplasm, preventing net Ca2+ loss. Mild presentation of RyR1 leak can occur under physiological conditions, providing fibre Ca2+ redistribution without changing fibre Ca2+ content. This condition preserves normal contractile function at the same time as increasing basal metabolic rate. However, higher RyR1 leak drives excess cytoplasmic and mitochondrial Ca2+ load, setting a deleterious intracellular environment that compromises the function of the skeletal muscle.

Tiny changes in cytoplasmic [Ca2+] cause large changes in mitochondrial Ca2+: what are the triggers and functional implications?

Ca²⁺ is an integral component of the functional and developmental regulation of the mitochondria. In skeletal muscle, Ca²⁺ is reported to modulate the rate of ATP resynthesis, regulate the expression of PGC1α following exercise and drive the generation of reactive oxygen species (ROS). Due to the latter, mitochondrial Ca²⁺ overload is recognized as a pathophysiological event but the former events represent important physiological functions in need of tight regulation. Recently, we described the relationship between [Ca²⁺]_mito and resting [Ca²⁺]_cyto and other mitochondrial Ca²⁺-handling properties of skeletal muscle. An important next step is to understand the triggers for Ca²⁺ redistribution between intracellular compartments, which determine the mitochondrial Ca²⁺ load. These triggers in both physiological and pathophysiological scenarios can be traced to the coupled activity of the ryanodine receptor 1 (RyR1) and store-operated Ca²⁺ entry (SOCE) in the resting muscle. In this piece we will discuss some issues regarding Ca²⁺ measurements relevant to mitochondrial Ca²⁺-handling, the steady state relationship between cytoplasmic and mitochondrial Ca²⁺ and the potential implications for Ca²⁺ handling by muscle mitochondria and cellular function.

Ryanodine receptor leak triggers fiber Ca2+ redistribution to preserve force and elevate basal metabolism in skeletal muscle

Muscle contraction depends on tightly regulated Ca²⁺ release. Aberrant Ca²⁺ leak through ryanodine receptor 1 (RyR1) on the sarcoplasmic reticulum (SR) membrane can lead to heatstroke and malignant hyperthermia (MH) susceptibility, as well as severe myopathy. However, the mechanism by which Ca²⁺ leak drives these pathologies is unknown. Here, we investigate the effects of four mouse genotypes with increasingly severe RyR1 leak in skeletal muscle fibers. We find that RyR1 Ca²⁺ leak initiates a cascade of events that cause precise redistribution of Ca²⁺ among the SR, cytoplasm, and mitochondria through altering the Ca²⁺ permeability of the transverse tubular system membrane. This redistribution of Ca²⁺ allows mice with moderate RyR1 leak to maintain normal function; however, severe RyR1 leak with RYR1 mutations reduces the capacity to generate force. Our results reveal the mechanism underlying force preservation, increased ATP metabolism, and susceptibility to MH in individuals with gain-of-function RYR1 mutations.

Pre-Operative Embolisation of Musculoskeletal Tumours - A Single Centre Experience

Introduction

The management of musculoskeletal tumours is complex and requires a multi-disciplinary approach. Preoperative embolisation can be often employed to reduce intra-operative blood loss and complication rates from surgery. We report our experience with the safety, technical success and efficacy of pre-operative embolisation in musculoskeletal tumours.

Materials and Methods

Thirteen consecutive patients who underwent pre-operative embolisation of a musculoskeletal tumour followed by surgical intervention at our institution from May 2012 to January 2016 were enrolled into the study. Patient demographics, tumour characteristics, embolisation techniques and type of surgery were recorded. Technical success of embolisation, amount of blood loss during surgery and transfusion requirements were estimated.

Results

There were five female and eight male patients who underwent pre-operative embolisation during the study period. The age ranged between 16 to 68 years, and the median age was 54. Technical success was achieved in all patients. Mean intra-operative blood loss was 1403ml, with a range of 150ml to 6900ml. Eight patients (62%) required intra-operative blood products of packed red blood cells and fresh frozen plasma. No major complications occurred during embolisation.

Conclusion

Pre-operative trans-arterial embolisation is feasible and safe for a variety of large and hypervascular musculoskeletal tumours. Our small series suggests that preoperative embolisation could contribute to the reduction of the intra-operative and post-operative blood product transfusion. It should be considered as a pre-operative adjunct for major tumour resections with a high risk of bleeding. The use of the haemoglobin gap complemented the assessment of perioperative blood loss.

Survey of neonatal unit outbreaks in North London: identifying causes and risk factors

BACKGROUND

This survey was undertaken after a number of neonatal unit (NNU) outbreaks were reported to the North London health protection teams (HPTs).

AIM

To determine the diversity of the outbreaks, ascertain potential sources and contributing factors, and identify the investigative procedures followed and control measures implemented.

METHODS

Using a structured questionnaire, information from the HPT database was collected for all NNU outbreaks reported between January 2010 and February 2011.

FINDINGS

Ten outbreaks were identified from seven hospitals in 14 months. There was one para-influenza outbreak, seven Staphylococcus aureus [including six meticillin-resistant S. aureus (MRSA)] outbreaks, and two Gram-negative outbreaks. Potential sources of transmission identified for the MRSA outbreaks were healthcare worker (HCW)-assisted transmission (N = 2) and mother-to-baby transmission with onward HCW-assisted transmission (N = 3). An environmental source with onward HCW-assisted transmission was documented for one of the Gram-negative outbreaks. Interventions included patient screening and enhanced cleaning (N = 10), isolating/cohorting affected neonates (N = 9), barrier nursing (N = 6), staff movement restrictions (N = 5), hand hygiene audits (N = 4), staff screening (N = 4), household contact screening (N = 3) and environmental sampling (N = 3). Potential contributing factors included inadequate staffing levels, cluttered unit, inadequate sterilization of communal milk-expressing equipment and inappropriate follow-up of MRSA results.

CONCLUSION

This survey determined the diversity of NNU outbreaks in North London, and highlighted the importance of a multi-faceted approach to outbreak control. These data will assist in the development of clinical standards for the prevention, control and reporting of NNU outbreaks, and guidance for best practice in NNUs.

Structures of proteins and cofactors: X-ray crystallography

Protein crystallography is the predominately used technique for the determination of the three-dimensional structures of proteins and other macromolecules. In this article, the methodology utilized for the measurement and analysis of the diffraction data from crystals is briefly reviewed. As examples of both the usefulness and difficulties of this technique, the determination of the structures of several photosynthetic pigment-protein complexes is described, namely, the reaction center from purple bacteria, photosystem I and photosystem II from cyanobacteria, the light-harvesting complex II from purple bacteria, and the FMO protein from green bacteria.

Specialist vaccination advice and pockets of resistance to MMR vaccination: lessons from an outbreak of measles

An outbreak of measles was associated with a private nursery school in north west London. Sixteen cases were identified of whom 13 were laboratory confirmed. The majority of cases were aged three years or younger. Older cases were siblings of younger cases. None of the cases had been vaccinated against measles. In the nursery school 33% of the children had not received MMR vaccination. Based on specialist advice from the Health Protection Agency the outbreak control team recommended that children with no history of MMR vaccination should have a first MMR dose as soon as possible and that children with one MMR dose should receive the second dose as soon as possible (minimum of one month between doses). Some parents had strong negative views about MMR and represented 'pockets of resistance' to vaccination advice. The specialist vaccination advice, which was different to national immunisation guidelines, also caused some confusion amongst other health professionals. With a decrease in MMR vaccination uptake and resulting increased potential for future measles outbreaks, clinicians should be aware of and understand specialist vaccination advice intended to deal with outbreaks.

Study on bionomics of principal malaria vectors in Kratie province, Cambodia

A cross-sectional study on bionomics of malaria was carried out in Kamlek village, Snuol rubber plantation, Kratie Province where the population had a high prevalence of malaria. Mosquitos were collected monthly between April to September 1998 from 18.00 hr to 6.00 hr by human bait and animal bait. Survey for larva breeding places was also performed. A total of 13 species of Anopheline mosquitos was collected, manly Anopheles philipinensis, An. aconitus, An. annularis, Ain. barbirostris, An. hyrcanus gr, An. jamesii, An. kawari, An. tesselatus, An. umbrosus and An. vagus. They were in various densities with the latter species being the most abundance. Among the vector species. An. maculatus was the most commonly collected with a density of 0.55 per man per night and peak biting was between 20.00 hr and 21.00 hr. The density of An. minimus and An. dirus were 0.11 and 0.74 per man per night with the peak biting time 24.00-01.00 hr and 20.00-21.00 hr respectively. Observation of host preference and feeding habit revealed An. maculatus to be exophagic, anthropophilic and 20 endophilic while An. minimus was both endophilic and exophagic and anthropophilic. An. dirus was endophilic and anthropophilic, these three species were not found positive for malaria infection. However, due to the limited time of survey and an exceptionally low rainfall in the rainy season, an inadequate sample was obtained for analysis. Therefore further investigation is required for at least a year for more information.

Compliance with advice to boil drinking water during an outbreak of cryptosporidiosis. Outbreak Investigation Team

All 2000 employees of a hospital in an area of the North Thames region where 300,000 households were advised to boil tap water before consumption during a large outbreak of cryptosporidiosis were surveyed about compliance with and adverse events linked to the boil water notice. Eighty-five per cent (408/479) of respondents who lived in the boil water area said that they used boiled water while the notice was in place, 72% (347) used bottled water, and 12% (59) did not continue to boil water for the whole 16 days. Although 88% believed that they were following the advice, 20% washed food that would be eaten raw in unboiled tap water and 57% used it to clean their teeth. If a boil water notice is applied for more than a few days it may be helpful to issue a detailed follow up letter.

Escherichia coli O157 incident associated with a farm open to members of the public

Three children, one who lived on an open farm and two who visited the farm in school parties, developed Vero cytotoxin producing Escherichia coli (VTEC) O157 infection in 1997. All had been in direct contact with animals. All were admitted to hospital with diarrhoea and two developed the haemolytic uraemic syndrome, one of whom developed severe neurological impairment. E.coli O157 phage type 21 that produced Vero cytotoxin 2 were isolated from the three children and from a goat paddock and two cows at the farm. The isolates were indistinguishable by molecular typing. The farm closed voluntarily for six weeks while recommendations to reduce the exposure of visitors to faecal contamination and to improve hygiene procedures (especially handwashing) were implemented. More research is needed into all aspects of VTEC O157 on farms, including the natural history of carriage in animals, the organism prevalence and factors that affect infectivity to humans. Further consideration is needed about the role of open farms in zoonoses, and how open farms can be assisted in reducing risks for visitors. The public need to be educated about the risks and about their responsibilities, which include the need to wash hands thoroughly and to avoid hand to mouth contact when visiting farms.

A large outbreak of cryptosporidiosis associated with a public water supply from a deep chalk borehole. Outbreak Investigation Team

Three hundred and forty-five confirmed cases were reported in a large waterborne outbreak of cryptosporidiosis in North Thames in the spring of 1997. The descriptive epidemiology, attack rates, a case control study, and the detection of oocysts in the water suggested strongly that the outbreak was associated with drinking unboiled tap water that originated from one deep chalk borehole. The 746,000 people living in the water distribution area were advised to boil their drinking water. Investigations did not reveal how oocysts entered the borehole. This is the first published report of a cryptosporidium outbreak caused by filtered borehole water and we believe it to be the largest outbreak due to groundwater to have been reported. Borehole supplies are regarded as relatively pure sources of water and this outbreak has implications for the future monitoring and treatment of drinking water extracted from boreholes.

Shigella outbreak in a school associated with eating canteen food and person to person spread

In June 1993 an outbreak of Shigella sonnei infection at a primary school in south east England affected 42% of 327 pupils and staff. Attack rates of diarrhoea and fever were 33% for children aged 4 to 8 years, and 8% for those aged 8 to 12 years (p < 0.00001). Illness was associated with eating canteen food (relative risk 5.9; 95% confidence interval 3.4, -10.3). All strains examined were S. sonnei phage type 3, with the same antibiogram (ttSTSS), and were indistinguishable using colicin typing and biotyping (colicin type 9, E8) and pulse field gel electrophoresis. Molecular epidemiology suggested but could not confirm that the outbreak strain was introduced into the school population from the community.

Immediate and long term outcome of human parvovirus B19 infection in pregnancy

OBJECTIVE

To estimate more precisely the risk of fetal loss and congenital abnormalities after maternal parvovirus B19 infection, and to assess the long term outcome for surviving infants.

DESIGN

Prospective cohort study of pregnant women with confirmed B19 infection with follow up of the surviving infants. The rate of fetal loss in the study cohort was compared with that in pregnant women with varicella.

SETTING

Cases reported by laboratories in England and Wales between 1985-1988 and 1992-1995.

SAMPLE

Four hundred and twenty-seven pregnant women with B19 infection and 367 surviving infants of whom 129 were followed up at 7-10 years of age.

METHODS

Questionnaires to obstetricians and general practitioners on outcome of pregnancy and health of surviving infants. Maternal infection confirmed by B19-specific IgM assay and/or IgG seroconversion.

RESULTS

The excess rate of fetal loss in women with B19 infection was confined to the first 20 weeks of gestation and averaged 9%. Seven cases of fetal hydrops followed maternal infections between 9 and 20 weeks of gestation (observed risk 2.9%, 95% CI 1.2-5.9). No abnormalities attributable to B19 infection were found at birth in surviving infants (observed risk 0%, upper 95% CI 0.86%). No late effects were found at 7-10 years.

CONCLUSIONS

Around 1 in 10 women infected before 20 weeks of gestation will suffer a fetal loss due to B19. The risk of an adverse outcome of pregnancy after this stage is remote. Infected women can be reassured that the maximum possible risk of a congenital abnormality due to B19 is under 1% and that long term development will be normal.

Audit of changes in serum urea and electrolytes following peri-operative intravenous fluid therapy

One thousand and eleven patients discharged from the postoperative recovery ward with intravenous infusions were reviewed in order to audit the extent of assessment of serum urea and electrolytes (U&Es) and the change in serum U&Es over the perioperative period. 69.7% had preoperative U&Es estimation, 42.5% had both a pre- and postoperative estimation and in 5%, only a postoperative estimate was undertaken. 12.2% of patients whose U&Es were measured had an abnormal preoperative serum potassium compared to 17.2% postoperatively (NS). Compared to a preoperative incidence of 13%, more patients (27.3%) had an abnormal postoperative serum sodium (p < 0.0001). There was a tendency towards postoperative hyponatraemia: 10.0% in the preoperative period compared to a postoperative 25.3% (p < 0.0001). More tests were performed in the elderly (83.9% in age > 65 years versus 69% in age 17-64-p < 0.0001) who were more likely to have electrolyte disturbances preoperative hypokalaemia (p < 0.05), postoperative hyperkalaemia (p < 0.05), postoperative hyponatraemia (p < 0.03) and raised serum urea, both pre- and postoperatively (p < 0.0001 and p < 0.0005 respectively). Patients undergoing intraabdominal procedures did not have significantly different peri-operative electrolyte abnormalities. Fewer tests were performed in emergency patients, who were hypokalaemic in the postoperative period compared to elective patients (p < 0.01). There was a higher incidence of preoperative hyponatraemia and raised serum urea in the emergency group (p < 0.001 and p < 0.0002 respectively). Neurosurgical emergencies often had a degree of preoperative hypokalaemia which persisted after surgery (p < 0.0001). Results indicate an increased risk of serum electrolyte abnormalities following peri-operative intravenous fluid therapy. However in the majority of patients, the magnitude of the change is not significant clinically.

Application of molecular methods to a nosocomial outbreak of Salmonella enteritidis phage type 4

A nosocomial outbreak of Salmonella enteritidis phage type 4 occurred in July 1995. Seven definite cases were identified over 13 days affecting four wards in a London hospital. The outbreak strain was characterized by plasmid profile typing and pulsed-field gel electrophoresis (PFGE), and was unusual in that it did not possess a 38 MDa plasmid common to most isolates of S. enteritidis PT 4 made from humans and food animals in England and Wales. Seven asymptomatic excreters were identified on screening. No additional cases occurred on wards after standard isolation procedures were implemented. No common or continuing food or dietary source was identified. Results of epidemiological, microbiological and environmental investigations suggested that the outbreak was due to person-to-person transmission within the hospital. The source of the outbreak was not established but was probably due to admission of a patient with an unrecognized infection of S. enteritidis PT 4. The study highlights the importance of close collaboration between hospital staff, epidemiologists and microbiologists, and demonstrates the value of molecular techniques for strain subdivision in outbreak investigations.

Parvovirus B19 outbreak on an adult ward

In November and December 1992, an outbreak of parvovirus B19 infection occurred among patients and staff on an adult mixed surgical ward at a large hospital in London. Three patients and 15 staff members were serologically confirmed as acute cases. The attack rate among susceptible members of staff was 47%. In those infected, arthralgia (80%) and rash (67%) were the most common symptoms. Of six susceptible in-patients on the ward, three became infected. One of the in-patients who had carcinoma of the mouth was viraemic for more than 10 days with marrow suppression resulting in the postponement of chemotherapy until intravenous immunoglobulin was given and he was no longer viraemic. Control measures taken included closure of the ward to new admissions, transfer of only immune staff to the ward, and restriction of the ward nursing staff to working only on that ward. Although no specific exposure was conclusively identified as a risk factor, there was a suggestion of an increased risk of acquiring parvovirus B19 infection among those staff who did not adopt strict hand washing procedures after each physical contact with a patient (RR = 2.33; P = 0.07). Knowledge of parvovirus B19 among interviewed health care workers was poor: only 42% reported knowing about parvovirus B19 and only 38% could name a patient category at risk of a severe outcome following infection. This is the first report of a nosocomial outbreak affecting an adult ward and of possible transmission of parvovirus B19 infection from staff to in-patients. Hospital control of infection teams should include parvovirus B19 in their outbreak containment plans.