Facilitated cross-bridge interactions with thin filaments by familial hypertrophic cardiomyopathy mutations in α-tropomyosin.

Familial hypertrophic cardiomyopathy (FHC) is a disease of cardiac sarcomeres. To identify molecular mechanisms underlying FHC pathology, functional and structural differences in three FHC-related mutations in recombinant α-Tm (V95A, D175N, and E180G) were characterized using both conventional and modified in vitro motility assays and circular dichroism spectroscopy. Mutant Tm's exhibited reduced α-helical structure and increased unordered structure. When thin filaments were fully occupied by regulatory proteins, little or no motion was detected at pCa 9, and maximum speed (pCa 5) was similar for all tropomyosins. Ca(2+)-responsiveness of filament sliding speed was increased either by increased pCa(50) (V95A), reduced cooperativity n (D175N), or both (E180G). When temperature was increased, thin filaments with E180G exhibited dysregulation at temperatures ~10°C lower, and much closer to body temperature, than WT. When HMM density was reduced, thin filaments with D175N required fewer motors to initiate sliding or achieve maximum sliding speed.

Spinal injuries after improvised explosive device incidents: implications for Tactical Combat Casualty Care.

BACKGROUND: Tactical Combat Casualty Care aims to treat preventable causes of death on the battlefield but deemphasizes the importance of spinal immobilization in the prehospital tactical setting. However, improvised explosive devices (IEDs) now cause the majority of injuries to Canadian Forces (CF) members serving in Afghanistan. We hypothesize that IEDs are more frequently associated with spinal injuries than non-IED injuries and that spinal precautions are not being routinely employed on the battlefield. METHODS: We examined retrospectively a database of all CF soldiers who were wounded and arrived alive at the Role 3 Multinational Medical Unit in Kandahar, Afghanistan, from February 7, 2006, to October 14, 2009. We collected data on demographics, injury mechanism, anatomic injury descriptions, physiologic data on presentation, and prehospital interventions performed. Outcomes were incidence of any spinal injuries. RESULTS: Three hundred seventy-two CF soldiers were injured during the study period and met study criteria. Twenty-nine (8%) had spinal fractures identified. Of these, 41% (n = 12) were unstable, 31% (n = 9) stable, and 28% indeterminate. Most patients were injured by IEDs (n = 212, 57%). Patients injured by IEDs were more likely to have spinal injuries than those injured by non-IED-related mechanisms (10.4% vs. 2.3%; p < 0.01). IED victims were even more likely to have spinal injuries than patients suffering blunt trauma (10.4% vs. 6.7%; p = 0.02). Prehospital providers were less likely to immobilize the spine in IED victims compared with blunt trauma patients (10% [22 of 212] vs. 23.0% [17 of 74]; p < 0.05). CONCLUSIONS: IEDs are a common cause of stable and unstable spinal injuries in the Afghanistan conflict. Spinal immobilization is an underutilized intervention in the battlefield care of casualties in the conflict in Afghanistan. This may be a result of tactical limitations; however, current protocols should continue to emphasize the judicious use of immobilization in these patients.

Utilization profile of the trauma intensive care unit at the Role 3 Multinational Medical Unit at Kandahar Airfield between May 1 and Oct. 15, 2009.

BACKGROUND: In the war against the Taliban, Canada was the lead North Atlantic Treaty Organization (NATO) nation to provide medical and surgical care to NATO soldiers, Afghanistan National Army soldiers, Afghanistan Nation Police, civilians working in and outside Kandahar Airfield and Afghanistan civilians at the Role 3 Multinational Medical Unit (R3MMU) from February 2006 to October 2009. METHODS: We obtained data from the Joint Theatre Trauma Registry between May 1 and Oct. 15, 2009; 188 patients were admitted to the R3MMU intensive care unit (ICU). We analyzed the ICU data according to types and causes of trauma, mechanical ventilation prevalence, ICU medical and surgical complications, blood products utilization, length of stay in the ICU and mortality. RESULTS: The admitting services were general surgery (35%), neurosurgery (29%), orthopedic surgery (18%) and internal medicine (3%). Improvised explosive devices (46%) and gunshot wounds (26%) were the main causes of ICU admissions. The mean injury severity score for all patients admitted to the ICU was 37, and 81% of ICU patients required mechanical ventilation for a mean duration of 3 days. The main ICU complications were coagulopathy (6.4%), aspiration pneumonia (4.3%), pneumothorax (3.7%) and wound infection (2.7%). The following blood products were most used: packed red blood cells (55%), fresh frozen plasma (54%), platelets (29%) and cryoprecipitate (23%). The average length of stay in the ICU was 4.3 days, and the survival rate was 93%. CONCLUSION: The high survival rate suggests that ICU care is a necessary and vital resource for a trauma hospital in a war zone.

Ca2+ sensitivity of regulated cardiac thin filament sliding does not depend on myosin isoform.

Myosin heavy chain (MHC) isoforms in vertebrate striated muscles are distinguished functionally by differences in chemomechanical kinetics. These kinetic differences may influence the cross-bridge-dependent co-operativity of thin filament Ca(2+) activation. To determine whether Ca(2+) sensitivity of unloaded thin filament sliding depends upon MHC isoform kinetics, we performed in vitro motility assays with rabbit skeletal heavy meromyosin (rsHMM) or porcine cardiac myosin (pcMyosin). Regulated thin filaments were reconstituted with recombinant human cardiac troponin (rhcTn) and alpha-tropomyosin (rhcTm) expressed in Escherichia coli. All three subunits of rhcTn were coexpressed as a functional complex using a novel construct with a glutathione S-transferase (GST) affinity tag at the N-terminus of human cardiac troponin T (hcTnT) and an intervening tobacco etch virus (TEV) protease site that allows purification of rhcTn without denaturation, and removal of the GST tag without proteolysis of rhcTn subunits. Use of this highly purified rhcTn in our motility studies resulted in a clear definition of the regulated motility profile for both fast and slow MHC isoforms. Maximum sliding speed (pCa 5) of regulated thin filaments was roughly fivefold faster with rsHMM compared with pcMyosin, although speed was increased by 1.6- to 1.9-fold for regulated over unregulated actin with both MHC isoforms. The Ca(2+) sensitivity of regulated thin filament sliding speed was unaffected by MHC isoform. Our motility results suggest that the cellular changes in isoform expression that result in regulation of myosin kinetics can occur independently of changes that influence thin filament Ca(2+) sensitivity.