The protection of bovine skeletal myofibrils from proteolytic damage post mortem by small heat shock proteins.

This study aimed to determine how small heat shock proteins (sHSPs) protect myofibrillar proteins from µ-calpain degradation during ageing. Immunoprecipitation experiments with M. longissimus dorsi (LD) from Angus heifers (n = 14) examined the interaction between αß-crystallin, desmin, titin, HSP20, HSP27 and µ-calpain. Results showed that αß-crystallin associated with desmin, titin, HSP20, HSP27 and µ-calpain. Exogenous αß-crystallin reduced desmin and titin degradations in myofibrillar extracts and attenuated µ-calpain activity. In a second experiment, bull LD (n = 94) were aged at -1.5°C for up to 28 days post mortem. µ-Calpain autolysed faster in high ultimate pH (pH(u)) meat (pH(u)≥6.2) and this was concomitant with the more rapid degradation of titin and filamin in this pH(u) group. Desmin stability in intermediate pH(u) meat (pH(u) 5.8 to 6.19) may be due to the protection of myofibril-bound sHSPs combined with the competitive inhibition of µ-calpain by sHSPs.

Small heat shock proteins and toughness in intermediate pHu beef.

Bull M. longissimus dorsi (n=94) categorised into high (n=28), intermediate (n=14) and low (n=52) ultimate pH (pHu) were aged at -1.5°C for 28days. Shear force was higher and more variable (p<0.05) in intermediate pHu samples during ageing. Titin, filamin and desmin degradation was also less extensive in intermediate pHu samples compared to the other two pH categories. The extent of the decline of HSP20, HSP27 and αß-crystallin concentrations during post mortem ageing was pHu related such that high pHu meat maintained the highest concentration of small heat shock proteins followed by intermediate and low pHu meat. µ-Calpain autolysis was slowest in intermediate pHu and cathepsin B activities remained consistently low during ageing in this group (p<0.05). Meat toughness in the intermediate pHu group may be attributed to the combination of a larger pool of sHSP with a sub-optimal cathepsin B activity and intermediary µ-calpain activities.

Variation in bull beef quality due to ultimate muscle pH is correlated to endopeptidase and small heat shock protein levels.

This study set out to determine if ultimate pH (pH(u)) affected the performance of intracellular small heat shock protein and endopeptidase dynamics in muscle during beef ageing. Longissimus dorsi muscles from 39 Angus or Limousin×Angus bulls were examined to see if pH(u) achieved at 22h post mortem (rigor) affected tenderness and water holding capacity of beef. Samples were segregated into three pH(u) groups termed high (pH>6.3), intermediate (5.73 days post mortem for intermediate pH(u) beef. High levels of alpha ß-crystallin (aßC) at 22h post mortem coincided with delayed muscle protein degradation for low pH(u) beef. Our results support the hypothesis that aßC shields myofibrils and buffers against endopeptidase degradation of beef structure during ageing.

Evaluation of a computerized arrhythmia alarm system.

A prospective study of a computerized arrhythmia alarm system was carried out in the coronary care unit during 200 patient hours of monitoring. The computer system was designed to activate an alarm on the development of rhythm and conduction disorders including asystole, ventricular tachycardia, atrial tachycardia, sinus tachtcardia, bradycardia, frequent premature ventricular beats, atrial fibrillation and bundle branch block. Study patients were simultaneously monitored by the computer system and a conventional analog heart rate alarm system. All alarms generated by the two systems were evaluated. Of 79 computer alarms, 42 (53 percent) were true positive alarms; during the same period there were 167 analog alarms of which only 13 (8 percent) were true positive alarms. In both systems, false positive alarms were primarily due to patient movement, but they occurred only 25 percent as often with the computer system as with the analog system. These results indicate that computerized arrhythmia monitoring systems offer significant advantages over conventional monitoring techniques.