High levels of docosahexaenoic acid (22 : 6n-3)-containing phospholipids in high-frequency contraction muscles of hummingbirds and rattlesnakes

Phospholipids containing docosahexaenoic acid (22:6n-3) have been proposed to be required as conformational cofactors for the functional assembly of m embrane proteins such as rhodopsin, ion pumps and the various complexes of the mitochondrial electron transport chain (Infante, 1987, Mol. Cell. Bioch em. 74, 111-116; Infante and Huszagh, 2000, FEBS Lett. 468, 1-5). This hypo thesis predicts that high-frequency contraction muscles, which are endowed with a high content of sarcoplasmic reticulum Ca2+-ATPase. (SERCA) and mito chondrial respiration enzymes, would have higher concentrations of 22:6n-3- containing phospholipids when compared with other muscles in the same speci es known to have a much lower contraction frequency. We have analyzed the f atty acid composition of ruby-throated hummingbird (Archilochus colubris) p ectoral and leg muscles and of rattlesnake (Crotalus atrox) shaker and vent ral muscles. We have found that hummingbird pectoral muscles, which are hig h contraction frequency muscles with the highest known respiratory rate amo ng vertebrates, have a 22:6n-3 concentration of 20.8% vs. 4.9% for the low frequency leg muscles. Similarly, rattler muscles in rattlesnakes, also hig h contraction frequency muscles, have a higher 22:6n-3 concentration than t hat of their ventral muscles (15.1% vs. 10.6%, respectively). These results are consistent with a specific molecular role for 22:6n-3-containing phosp holipids, as proposed. (C) 2001 Elsevier Science Inc. All rights reserved.