When these mutant channels are expressed in human embryonic kidney (HEK 293)  cells, the resulting channels are five times more sensitive to activation by caffeine (and presumably halothane) and activate at 5–10mV more hyperpolarized. Furthermore, cells expressing these channels have an increased basal cytosolic Ca2+ concentration. As these channels interact with and activate RYR1, these alterations result in a drastic increase of intracellular Ca2+, and, thereby, muscle excitability.Other mutations causing MH have been identified, although in most cases the relevant gene remains to be identified. Animal model
Research into malignant hyperthermia was limited until the discovery of "porcine stress syndrome" (PSS) in Danish Landrace and other pig breeds selected for muscling, a condition in which stressed pigs develop "pale, soft, exudative" flesh (a manifestation of the effects of malignant hyperthermia) rendering their meat less marketable at slaughter. This "awake triggering" was not observed in humans, and initially cast doubts on the value of the animal model, but subsequently, susceptible humans were discovered to "awake trigger" (develop malignant hyperthermia) in stressful situations. This supported the use of the pig model for research. Pig farmers use halothane cones in swine yards to expose piglets to halothane. Those that die were MH-susceptible, thus saving the farmer the expense of raising a pig whose meat he would not be able to market. This also reduced the use of breeding stock carrying the genes for PSS. The condition in swine is also due to a defect in ryanodine receptors.Gillard et al.
These include a raised creatine kinase level, elevated potassium, increased phosphate (leading to decreased calcium) and—if determined—raised myoglobin; this is the result of damage to muscle cells. Severe rhabdomyolysis may lead to acute kidney failure, so kidney function is generally measured on a frequent basis. Patients may also experience premature ventricular contractions due to the increased levels of potassium released from the muscles during episodes. Susceptibility testing
Muscle testing
The main candidates for testing are those with a close relative who has had an episode of MH or have been shown to be susceptible. The standard procedure is the "caffeine-halothane contracture test", CHCT. A muscle biopsy is carried out at an approved research center, under local anesthesia. The fresh biopsy is bathed in solutions containing caffeine or halothane and observed for contraction; under good conditions, the sensitivity is 97% and the specificity 78%. Negative biopsies are not definitive, so any patient who is suspected of MH by their medical history or that of blood relatives is generally treated with non-triggering anesthetics, even if the biopsy was negative. Some researchers advocate the use of the "calcium-induced calcium release" test in addition to the CHCT to make the test more specific.Less invasive diagnostic techniques have been proposed. Intramuscular injection of halothane 6 vol% has been shown to result in higher than normal increases in local pCO2 among patients with known malignant hyperthermia susceptibility. The sensitivity was 100% and specificity was 75%.