THE 2012 WAGS/PROQUEST DISTINGUISHED MASTER'S THESIS AWARD:

Jacqueline Kiwata, California State University

The Effect of Vigorous Exercise on the Content of Cholesteryl Linoleate, a Novel Antimicrobial Effector Molecule, in Upper Respiratory Tract Secretions

Consistent exercise performed at moderate to vigorous intensity 3-5 times a week is associated with reduced incidence of upper respiratory tract infection (URI). Innate mucosal immunity of the upper respiratory tract likely aids in the prevention of URI through the actions of key effector molecules such as lysozyme (Lys), an antimicrobial polypeptide. We have recently shown that antimicrobial lipids including cholesteryl linoleate (CL) are also important for the antimicrobial activity of airway fluid. However, the contributions of these molecules immediately post-exercise are unclear. We propose that habitual, vigorous exercise causes increases in antimicrobial molecule content in airway secretions, thus decreasing host susceptibility to URI. To investigate the acute effects of vigorous aerobic exercise on CL and Lys in respiratory secretions, nasal fluid was collected from 14 consistently active individuals (ACT) (32±11 yrs, 7 males, 7 females) and 14 inactive controls (INA) (25±3 yrs, 7 males,7 females) before (PRE) and immediately after (POST) 20 min of treadmill exercise at ~70% of maximal oxygen uptake. CL analysis employed reversed-phase HPLC with quantitative light scattering detection on total lipid extracts, while Lys was analyzed using lysoplate assay. Fold change in CL was significantly increased after exercise for ACT (p = 0.026 in MANCOVA), and fold change in total nonpolar lipids was significantly increased after exercise for ACT males (p=0.039 in MANCOVA). An upward trend in mean Lys was observed in both ACT and INA PRE to POST, but this increase was not significant. These data suggest that, in contrast to INA, moderate to vigorous exercise effects significant increases in the airway concentrations of nonpolar lipids in ACT, with the antimicrobial lipid cholesteryl linoleate showing the greatest rise PRE to POST. These findings agree with the documented, reduced incidence of URI in regularly exercising individuals.

THE 2012 WAGS/PROQUEST INNOVATION IN TECHNOLOGY AWARD:

Tim Leonard, University of Calgary

Force Production in Lengthened Myofibrils and Single Sarcomeres

The prior contractile history of skeletal muscle influences the steady-state isometric force generated, but there is little agreement on the underlying mechanism for this variation in active force. The most commonly held mechanism for residual force enhancement following active muscle stretching involves rapid and un-controlled sarcomere length re-distribution (“popping”). To gain insight into this behaviour, experiments were performed on rabbit psoas muscle myofibrils where all individual sarcomere lengths could be determined simultaneously with force during isometric and eccentric contractions. Specialized silicon-nitride cantilevers were fabricated in a nano-scale facility and the dimensions of the devices were optimized to the requirements of the different types of experiments (active, passive, or titin-deleted). The optics of the imaging system was optimized to a resolution of 6.7 nm/pixel and the forces measured were in the nanoNewton range. Single isometrically activated and then stretched myofibrils showed force-enhancement following stretch and sarcomere length non-uniformities were detected, but no “popping” was observed. Therefore, experiments were conducted on myofibrils reduced to a single sarcomere, preventing the possibility of non-uniform sarcomeres playing a role in the extra force following stretch. Enhanced force was observed in these single sarcomere preparations uniquely demonstrating that force enhancement can occur in the absence of sarcomere “popping”. Finally, the role of titin in actively and passively lengthened myofibrils was investigated to determine whether the enhanced force following active stretch could be attributed to this molecular spring. Single myofibrils were lengthened from the plateau region of the force-length relationship to very long sarcomere lengths where actin-myosin filament overlap was lost, with and without titin, and it was determined that titin is crucial for force production in actively and passively lengthened myofibrils. Activated myofibrils lengthened to sarcomere lengths far beyond where actin-myosin filament overlap occurs, unexpectedly produced four times higher forces compared to passively lengthened myofibrils at the same length. These results suggest that the molecular spring titin plays a major role in sarcomere mechanics and that history dependent behaviour likely originates from a parallel elastic element and not from sarcomere length redistribution. A three-filament model of skeletal muscle (actin, myosin and titin) may need to become the accepted model of muscle contraction if we are to explain muscle behaviour more completely.