Myoglobin saturation in free-diving Weddell seals

Abstract

Although the consumption of myoglobin-bound O2 (MbO2) stores in seal muscles has been demonstrated in seal muscles during laboratory simulations of diving, this may not be a feature of normal field diving in which measurements of heart rate and lactate production show marked differences from the profound diving response induced by forced immersion. To evaluate the consumption of muscle MbO2 stores during unrestrained diving, we developed a submersible dual-wavelength laser near-infrared spectrophotometer capable of measuring MbO2 saturation in swimming muscle. The probe was implanted on the surface of the latissimus dorsi of five subadult male Weddell seals (Leptonychotes weddelli) released into a captive breathing hole near Ross Island, Antarctica. Four seals had a monotonic decline of muscle O2 saturation during free diving to depths up to 300 m with median slopes of -5.12 +/- 4.37 and -2.54 +/- 1.95%/min for dives lasting < 17 and > 17 min, respectively. There was no correlation between the power consumed by swimming and the desaturation rate. Two seals had occasional partial muscle resaturations late in dives, indicating transfer of O2 from circulating blood to muscle myoglobin. Weddell seals partially consume their MbO2 stores during unrestrained free diving.

Myoglobin: A scavenger of bioactive NO

“…Mb serves as a short-term O 2 reservoir in exercising skeletal muscle and in the beating heart, tiding the muscle over from one contraction to the next (4). In diving mammals, the concentrations of Mb exceed those of terrestrial mammals up to 10-fold, and Mb most likely serves for the extension of diving time when pulmonary ventilation ceases (5). Similarly, in mammals and humans adapted to high altitudes, Mb is expressed in high concentrations in skeletal muscle (6).…”

Scaling matters: incorporating body composition into Weddell seal seasonal oxygen store comparisons reveals maintenance of aerobic capacities

“…Moreover, pinnipeds are adapted to utilize O 2 stores efficiently, comprising the graded dive response. At the onset of a deep dive, seals exhibit bradycardia and employ peripheral vasoconstriction to apportion blood O 2 stores to specific tissues (Butler and Jones 1997;Guyton et al 1995;Davis et al 2004), such as the heart, lung, and brain (Zapol et al 1979). Diverting blood O 2 stores primarily to anoxia intolerant organs means that skeletal muscles are often un-perfused (Zapol et al 1979;Guyton et al 1995;Davis et al 2004;Williams et al 2011).…”

“…At the onset of a deep dive, seals exhibit bradycardia and employ peripheral vasoconstriction to apportion blood O 2 stores to specific tissues (Butler and Jones 1997;Guyton et al 1995;Davis et al 2004), such as the heart, lung, and brain (Zapol et al 1979). Diverting blood O 2 stores primarily to anoxia intolerant organs means that skeletal muscles are often un-perfused (Zapol et al 1979;Guyton et al 1995;Davis et al 2004;Williams et al 2011). To withstand this reduction of vascular O 2 supply during periods of underwater activity, pinniped skeletal muscles have 10-20-fold the amount of myoglobin (Mb) compared to terrestrial mammals (Reed et al 1994;Guyton et al 1995;Kanatous et al 1999;Polasek et al 2006).…”

“…Diverting blood O 2 stores primarily to anoxia intolerant organs means that skeletal muscles are often un-perfused (Zapol et al 1979;Guyton et al 1995;Davis et al 2004;Williams et al 2011). To withstand this reduction of vascular O 2 supply during periods of underwater activity, pinniped skeletal muscles have 10-20-fold the amount of myoglobin (Mb) compared to terrestrial mammals (Reed et al 1994;Guyton et al 1995;Kanatous et al 1999;Polasek et al 2006).…”

“…The ADL can be estimated by dividing endogenous O 2 stores by diving metabolic rates (DMR), which is an accurate estimator of the diving lactate threshold in Weddell seals (Kooyman et al 1980(Kooyman et al , 1983Ponganis et al 1993;Burns and Castellini 1996;Costa et al 2001). The diving lactate threshold, or the "true" ADL, will vary on a dive-by-dive basis depending on O 2 saturation at the start of a dive, the magnitude of the dive response, and metabolic rates (Castellini et al 1992b;Guyton et al 1995;Davis and Kanatous 1999). However, given the difficulty of measuring the diving lactate threshold in free-living animals, the calculated (c)ADL is used as a proxy (Costa et al 2001Costa and Sinervo 2004).…”