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First published online October 7, 2008
Journal of Experimental Biology 211, 3323-3332 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.018887

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Blood flow and metabolic regulation in seal muscle during apnea

Paul J. Ponganis¹, Ulrike Kreutzer², Torre K. Stockard¹, Ping-Chang Lin², Napapon Sailasuta³, Tuan-Khan Tran², Ralph Hurd³ and Thomas Jue^2,*

¹ Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
² Department of Biochemistry and Molecular Medicine, University of California Davis, Davis, CA 95616, USA
³ GE Medical Systems, Fremont, CA 94539, USA

^* Author for correspondence (e-mail: TJue{at}ucdavis.edu)

Accepted 19 August 2008

In order to examine myoglobin (Mb) function and metabolic responses of seal muscle during progressive ischemia and hypoxemia, Mb saturation and high-energy phosphate levels were monitored with NMR spectroscopy during sleep apnea in elephant seals (Mirounga angustirostris). Muscle blood flow (MBF) was measured with laser-Doppler flowmetry (LDF). During six, spontaneous, 8–12 min apneas of an unrestrained juvenile seal, apneic MBF decreased to 46±10% of the mean eupneic MBF. By the end of apnea, MBF reached 31±8% of the eupneic value. The t_1/2 for 90% decline in apneic MBF was 1.9±1.2 min. The initial post-apneic peak in MBF occurred within 0.20±0.04 min after the start of eupnea. NMR measurements revealed that Mb desaturated rapidly from its eupenic resting level to a lower steady state value within 4 min after the onset of apnea at rates between 1.7±1.0 and 3.8±1.5% min^–1, which corresponded to a muscle O₂ depletion rate of 1–2.3 ml O₂ kg^–1 min^–1. High-energy phosphate levels did not change with apnea. During the transition from apnea to eupnea, Mb resaturated to 95% of its resting level within the first minute. Despite the high Mb concentration in seal muscle, experiments detected Mb diffusing with a translational diffusion coefficient of 4.5x10^–7 cm² s^–1, consistent with the value observed in rat myocardium. Equipoise P_O2 analysis revealed that Mb is the predominant intracellular O₂ transporter in elephant seals during eupnea and apnea.

Key words: Doppler, muscle, myoglobin, NMR, oxygen, hemodynamics

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