Flight muscle carnitine palmitoyl transferase activity varies with substrate chain length and unsaturation in the hoary bat (Lasiurus cinereus)

Abstract

Fat is an important fuel for bats to support high metabolic rates in extended periods of flight. The fatty acid composition of adipose stores could affect whole animal exercise performance, as fatty acids vary in rates of mobilization and oxidation. A key step in the fatty acid oxidation pathway is transporting fatty acids from the cytosol into mitochondria, mediated by the enzyme carnitine palmitoyl transferase (CPT). Therefore, understanding the substrate preference patterns of CPT in bats is important for interpreting the consequences of adipose fatty acid profiles. We measured CPT activity with eight different fatty acyl CoA substrates (16:0, 16:1ω7, 18:0, 18:1ω9, 18:2ω6, 18:3ω3, 20:4ω6, and 22:6ω3) in the pectoralis muscle of migrating and nonmigrating hoary bats (Lasiurus cinereus (Beauvois, 1796)). The pattern of substrate preference was similar to the patterns previously reported for birds and rats and was not affected by migration. Generally, activity increased with the number of double bonds and was higher with 16 carbon fatty acids compared with 18 carbon fatty acids. Given the observed substrate variation in CPT activity, there is no evidence to suggest that recently reported seasonal changes in the adipose fatty acid composition of migrating hoary bats would lead to increased lipid oxidation rate, and may instead be a consequence of seasonal shifts in diet.