Metabolism of perfused pig intercostal muscles evaluated by 31P-magnetic resonance spectroscopy

This study presents a perfused preparation for evaluation of metabolism in pig intercostal muscle in vitro . Preserved vessels and nerves to an intercostal segment including two adjacent ribs allowed for tissue perfusion and electrical stimulation with measurement of contraction force, oxygen consumption and 31 P-magnetic resonance spectroscopy ( 31 P-MRS). When perfused at rest with Krebs–Ringer buffer, the preparation maintained physiological levels of phosphocreatine (PCr), inorganic phosphate (P i ), ATP and pH at a stable oxygen consumption of 0.51 ± 0.01 μmol min −1 g −1 for more than 2 h. Tonic stimulation of the nerve caused anaerobic energy consumption as PCr and pH decreased, and both variables recovered after the contraction with half-time values of ∼7 min. Force increased to 0.040 N g −1 (range, 0.031–0.103 N g −1 ) and it gradually decreased by about 70% during the subsequent 5 min of stimulation. The calculated free ADP concentration increased from 7.4 ± 2.1 nmol g −1 at rest to 28 ± 12 nmol g −1 (mean ± s.d. ) by the end of the stimulation. Thus anaerobic ATP turnover was zero at rest, 6.1 ± 2 μmol min −1 g −1 during the first minute of stimulation and 3.5 ± 0.5 μmol min −1 g −1 during the two last minutes, corresponding to the drop in force. When the preparation was left unperfused, anaerobic ATP turnover averaged 0.40 ± 0.15 μmol min −1 g −1 for the first 10 min. The preparation can also be applied to human intercostal muscles, as demonstrated in one preliminary experiment. The results demonstrate a stable and functional in vitro preparation of intact perfused intercostal muscles in the pig.