Abstract
As marine divers, pinnipeds have a high capacity for exercise at depth while holding their breath. With finite access to oxygen, these species need to be capable of extended aerobic exercise and conservation of energy. Pinnipeds must deal with common physiological hurdles, such as hypoxia, exhaustion and acidosis, that are common to all exercising mammals. The physiological mechanisms in marine mammals used for managing oxygen and carbon dioxide have sparked much research, but access to animals and tissues is difficult and requires permits. Deceased animals that are either bycaught or stranded provide one potential source for tissues, but the validity of biochemical data from post-mortem samples has not been rigorously assessed. Tissues collected from stranded diving mammals may be a crucial source to add to our limited knowledge on the physiology of some of these animals and important to the conservation and management of these species. We aim to determine the reliability of biochemical assays derived from post-mortem tissue and to promote the immediate sampling of stranded animals for the purpose of physiological research. In this study, we mapped the temporal degradation of muscle enzymes from biopsied Northern elephant seals (Mirounga angustirostris) and highlight recommendations for storage protocols for the best preservation of tissue. We also compared the enzymatic activity of different muscle groups (pectoral and latissimus dorsi) in relation to locomotion and measured the effects of four freeze-thaw cycles on muscle tissue enzyme function. Results indicate that enzymatic activity fluctuates greatly, especially with varying storage temperature, storage time, species and muscle group being assayed. In contrast, proteins, such as myoglobin, remain relatively continuous in their increase at 4°C for 48 h. Stranded animals can be a valuable source of biochemical data, but enzyme assays should be used only with great caution in post-mortem tissues.
Highlights
IntroductionMuscle tissue samples collected in vivo have provided a vast amount of knowledge on the physiology, exercise performance and basic muscle structure of marine mammals (Kanatous et al, 1999, 2008; Dearolf et al, 2000; Watson et al, 2003; Trumble et al, 2010; Kielhorn et al, 2013; Velten et al, 2013)
The lactate dehydrogenase (LDH) activity level was higher in tissues maintained at 4°C over a 24 h period
For three of the four marine mammals the primary locomotory muscle used had elevated Citrate synthase (CS) activity (Fig. 5). Enzymatic assays, such as for CS and LDH, may not provide reliable results, because the enzymes tend to be relatively unstable over 24 h at both room (21°C) and refrigerator temperature (4°C)
Summary
Muscle tissue samples collected in vivo have provided a vast amount of knowledge on the physiology, exercise performance and basic muscle structure of marine mammals (Kanatous et al, 1999, 2008; Dearolf et al, 2000; Watson et al, 2003; Trumble et al, 2010; Kielhorn et al, 2013; Velten et al, 2013). Between 1999 and 2014, there have been approximately twice as many published papers using biopsy sampling in marine mammal research in comparison to post-mortem specimens (Kanatous et al, 2002, 2008; Ponganis et al, 2002; Burns et al, 2005; Noren et al, 2005; Richmond et al, 2006; Clark et al, 2007; Spence-Bailey et al, 2007; Hindle et al, 2009; Prewitt et al, 2010; Shero et al, 2012). There are a number of conditions that contribute or add to proteolysis, such as enzymatic activity (Geesink et al, 2006), temperature (Morita et al, 1996), disease state (Costelli et al, 2005), pH (Eijsink et al, 2005) and level of muscle atrophy (Kachaeva and Shenkman, 2012)
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