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MHAUS is fortunate to have many of the world's experts on MH serving currently or in the past on our hotline and/or Professional Advisory Council. I will therefore from time to time, ask one of them to fill in for me in writing the monthly blog. Dr. Tom Nelson, who is now retired, spent many years researching the presentation and pathophysiology of MH in animals and in man. I and members of the MH community have learned a great deal from him. I think you will enjoy reading his views on Calcium.
Having just completed my PhD in animal nutrition I was uncertain where and how I would pursue my profound interest in the role of calcium as a messenger in cellular events. The veterinary surgeon, Dr. Wynn Jones, DVM, PhD, who did the parathyroid/thyroparathyroidectomies for my thesis study invited me to join him in his research on nutrition-disease interactions. His work involved obtaining “germ-free” newborn pigs by C-section and maintaining them in a germ-free environment. A young veterinarian, Dr. Ian Anderson DVM, PhD, from New Zealand had arrived for a postdoctoral study and was responsible for the anesthesia and surgery of the mother pigs. Several of these died during anesthesia and Dr. Anderson’s abilities were brought into question. Eventually, Dr. Jones invited a clinical (human) anesthesiologist, the late Dr. Tom Burnap, MD to come and investigate why these mother pigs were dying so unexpectedly under halothane anesthesia. Dr. Burnap had just read an article about anesthesia-related hyperthermic deaths in humans that was thought to be familial. Dr. Jones decided to pursue the matter and eventually characterized the MH syndrome in purebred Poland China pigs. I played a role in establishing a relationship between porcine stress syndromes and MH in our pigs. The porcine stress syndrome was a serious problem for pork production, costing millions of dollars in losses.
I had a strong background in biochemistry and Dr. Jones asked me to establish a test for MH by measuring ATP levels in the pig’s muscle. Indeed, we could predict the MH status of the pigs by the ATP test and, due to my calcium interests, I decided to see if removal of calcium from the muscle bath would make a difference and it did. With calcium absent, the MH muscle did not react abnormally. (This was one of the most important clues that calcium regulation was involved in MH) At this point I became fascinated by the MH syndrome and decided to do further testing on calcium regulation in MH skeletal muscle. I was hooked! For 4 years I tried to get NIH funding for MH studies but was unsuccessful (my NIH pink slip stated that “it is uncertain if this disease exists”) and decided to accept an invitation from Dr. Michael Denborough (the first to report MH) to do a fellowship in his lab in Canberra, Australia. During my stay in Australia I helped Dr. Denborough locate MH pigs (a lot of face-mask halothane anesthesia in pig pens!) and I began to work on human skeletal muscle in the lab. As a consequence of this I was able to establish an MH testing laboratory when I returned to the USA. Dr. Trey Flewellen and I established the MH diagnostic laboratory and an MH pig colony for many fruitful research projects at the University of Texas Medical Branch in Galveston. BTW after returning to the USA I was funded by the NIH for MH studies over the next 21 years!
Certain that calcium regulation was involved in MH, we sought to determine exactly where that defect lay. It was fairly easy to isolate the membrane from skeletal muscle that is involved in calcium regulation (the sarcoplasmic reticulum). At that time it was possible to measure the pump that removes calcium and makes the muscle relax so we first tested it. As it turned out, the pump was not only normal but when exposed to halothane it worked even better! This could not explain MH. If calcium uptake was not the answer, then the processes involved with releasing calcium and causing muscle contraction remained a good possibility. Ion channels were just being recognized as molecular entities at this time and very few investigators could measure them and most were looking at potassium and sodium channels. Working with Dr. Stan Ohnishi in my lab, we were able to load calcium into the isolated sarcoplasmic reticulum membranes and then cause the membranes to release calcium; presumably thru a calcium channel. Both Dr. Ohnishi and I were ultimately able to show that MH involved the abnormal release of calcium thru this calcium channel. The calcium channel (named the ryanodine receptor) was isolated and identified in Dr. Gerhard Meissner’s lab and the gene responsible for coding the calcium channel was discovered in Dr. David MacLennan’s lab. This led to the discovery of mutations in the calcium channel gene that linked to MH susceptibility. Yes, calcium is important in the regulation of cellular events but if the processes regulating calcium become faulty, then bad things can happen. Anesthetic-induced MH happens to be one of these bad things because these drugs cause the mutant calcium channel to open abnormally and increase calcium in the muscle cell, triggering the syndrome.
Thomas Nelson, MD
Wake Forest University School of Medicine