Construction and Expression of Ryanodine Receptor Mutants Relevant to Malignant Hyperthermia Patients in Japan

Malignant hyperthermia (MH) is a potentially fatal pharmacogenetic disorder triggered by exposure to commonly used volatile anesthetics. Pharmacological and genetic analyses implicated the type 1 of ryanodine receptor (RyR1) /Ca2+ release channel as the main candidate gene for causing MH. Genetic diagnosis of MH was proposed to replace conventional methods using biopsied muscle samples that are painful for patients and require skillful diagnosticians to interpret. However, more than 250 RyR1 gene variants have now been reported in MH-susceptible patients, although most have yet to be associated with functional abnormalities using exogenous constructs of these mutants expressed in living cells. To directly compare the pharmacological characteristics of some of the MH-related RyR1 mutants, we have established doxycycline -inducible cell lines expressing two of the unconfirmed rabbit RyR1 mutants, Q156K or R534H (corresponding to the Q155K or R533H mutations in human RyR1 reported in MH patients in Japan) and a confirmed mutant, R164C RyR1 (corresponding to the R163C mutation in human). The caffeine sensitivity of Q156K-expressing cells was remarkably enhanced compared to wild-type RyR1 and similarly to previously reported levels for R164C-expressing cells, while that of the R534H mutants was not different from wild-type cells. The resting cytosolic Ca2+ concentrations of cell lines expressing Q156K or R164C were much higher than those expressing R534H or wild-type RyR1. These results indicated that the RyR1 gene mutation causing the Q156K phenotype (Q155K in human) is potentially susceptible to MH, and that screening for this mutation could be useful for the noninvasive genetic diagnosis of MH in humans

Experimental investigation of an optimum configuration for a high-voltage photoemission gun for operation at ≥500 kV

We demonstrated the generation of a 500-keV electron beam from a high dc voltage photoemission gun for an energy recovery linac light source [N. Nishimori et al., Appl. Phys. Lett. 102, 234103 (2013)]. This demonstration was achieved by addressing two discharge problems that lead to vacuum breakdown in the dc gun. One is field emission generated from a central stem electrode. We employed a segmented insulator to protect the ceramic insulator surface from the field emission. The other is microdischarge at an anode electrode or a vacuum chamber, which is triggered by microparticle transfer or field emission from a cathode electrode. An experimental investigation revealed that a larger acceleration gap, optimized mainly to reduce the surface electric field of the anode electrode, suppresses the microdischarge events that accompany gas desorption. It was also found that nonevaporable getter pumps placed around the acceleration gap greatly help to suppress those microdischarge events. The applied voltage as a function of the total gas desorption is shown to be a good measure for finding the optimum dc gun configuration

High-voltage testing of a 500-kV dc photocathode electron gun

A high-voltage dc photocathode electron gun was successfully conditioned up to a voltage of 550 kV and a long-time holding test for 8 h was demonstrated at an acceleration voltage of 500 kV. The dc photocathode electron gun is designed for future light sources based on energy-recovery linac and consists of a Cockcroft-Walton generator, a segmented cylindrical ceramic insulator, guard-ring electrodes, a support-rod electrode, a vacuum chamber, and a pressurized insulating gas tank. The segmented cylindrical ceramic insulator and the guard-ring electrodes were utilized to prevent any damage to the insulator from electrons emitted by the support-rod electrode