Changing myoglobin’s paradigm: a novel link between lipids and myoglobin (537.4)

Abstract

During endurance exercise, terrestrial mammals rely on erythrocytic oxygen to fuel aerobic metabolism in working muscle. Physiological changes associated with endurance training elicit responses that increase muscular blood flow and subsequent oxygen delivery . Intramuscular oxygen stores, alternatively, appear to bear little significance in sustaining aerobic metabolism during endurance exercise, evident by the inability to appreciably release intra‐muscular stored oxygen during normoxic exercise; yet, terrestrial endurance athletes have more myoglobin (Mb) than their sedentary counterparts. Accordingly, Mb’s traditional functional paradigm pertaining to oxygen storage and transport does not appear to be fully applicable to terrestrial mammals in vivo. Here, we provide data offering alternative paradigm, where increases in Mb expression were associated with increases in lipid supplementation. C2C12 cells were cultured in normoxic or hypoxic conditions with glucose or 5% lipid. Mb assays and western blots revealed lipid hypoxic cells had higher Mb than glucose hypoxic cells and both lines of normoxic cells. Normoxic cells were also compared to soleus tissue from normoxic rats fed a high fat diet; both normoxic high fat conditions showed no change in carbon monoxide (CO)‐binding Mb, but increased total Mb protein, suggesting an increase in non‐CO‐binding Mb. Moreover, Mb increases did not parallel CN increases, but did, however, parallel increases in lipid supplementation and oxidative stress markers, suggesting an alternative pathway for Mb regulation associated with lipid and independent of CN. In light of these novel data, and in conjunction with the inability of terrestrial mammals to appreciably utilize Mb oxygen stores, we propose an alternative paradigm, whereby in the context of lipid metabolism, Mb as an oxygen store appears less relevant than Mb as scavenger of reactive oxygen species or potential transporter.