Carbohydrate and fat in energy metabolism of red and white muscle

Abstract

The ability of the mitochondria from red and white skeletal muscle of rabbit to oxidize various substrates with coupled phosphorylation was determined to evaluate the relative capacities of the two muscle types to utilize carbohydrate and fat for aerobic energy production. The respiratory rates were highest with pyruvate and were similar with mitochondria of red and white muscle. Compared to pyruvate, respiration with (-)palmitoylcarnitine and (-)-acetylcarnitine was only slightly slower in red but nearly half as great in white muscle mitochondria. The ADP/O values were similar with pyruvate and (-)-acetylcarnitine but lower during (-)-palmitoylcarnitine oxidation. The activities of palmitate-activating enzyme and carnitine acyltransferases were twice as high in red as in white muscle mitochondria. Thus, white muscle, and to some extent red muscle, appears potentially capable of deriving more usable energy by oxidizing carbohydrate than fat, and this correlates with the known observations that in vigorously exercising muscle carbohydrate utilization predominates over that of fat.

Ketogenesis in rat‐liver mitochondria: Stimulation by palmityl‐coenzyme A

“…A similar effect is displayed by palmityl-CoA as demonstrated recently with isolated mitochondria of rat heart [7] and rat liver [5,6,8-lo].…”

Protein composition and function of red and white skeletal muscle mitochondria

“…The disproportionate contamination between mitochondrial types before using the Percoll gradient may explain some of the discrepancies in the literature. Previous studies looking at differences in maximal respiration between mitochondria from red and white muscle have found State 3 respiration with PϩM higher in red (24,36) or no different (2,7,40,47,54); with GϩM, higher in white (10) or no different (47); with succinate, higher in red (7) or no different (47); and with PCϩM, higher in red (24,36,40). Of these studies, only Schwerzmann et al (47) reported using a Percoll gradient, and, similar to our results (Fig.…”

“…However, Schwerzmann and colleagues (47) found no difference in State 3 respiration with PϩM, glutamate ϩ malate (GϩM), or succinate in mitochondria isolated from cat soleus and gracilis. Furthermore, while Pande and Blanchaer (40) found no difference with PϩM, they did find higher State 3 respiration with PCϩM in mitochondria from red muscle compared with white. These conflicting results necessitate a deeper look into potential differences between mitochondria from red and white skeletal muscle.…”

Inhibition by fatty acyl esters of adenine nucleotide translocation in rat‐liver mitochondria

“…the presence of rotenone is strictly required because otherwise acylcarnitines are oxidized too fast to give any inhibition [cf. 6,8]. Only addition of long-chain acylcarnitines leads to an appreciable inhibition of ATPase activity.…”