( hile cells continue to produce the same...)Lactic acid not athlete's poison, but an energy source - if you know how to use it

hile cells continue to produce the same amount of lactate. This implied that, somehow, cells adapt during training to put out less waste product. He postulated an "intracellular lactate shuttle" that transports lactate from the cytoplasm, where lactate is produced, through the mitochondrial membrane into the interior of the mitochondria, where lactate is burned. In 2000, he showed that endurance training increased the number of lactate transporter molecules in mitochondria, evidently to speed uptake of lactate from the cytoplasm into the mitochondria for burning.

The new paper and a second paper to appear soon finally provide direct evidence for the hypothesized connection between the transporter molecules - the lactate shuttle - and the enzymes that burn lactate. In fact, the cellular mitochondrial network, or reticulum, has a complex of proteins that allow the uptake and oxidation, or burning, of lactic acid.

"This experiment is the clincher, proving that lactate is the link between glycolytic metabolism, which breaks down carbohydrates, and oxidative metabolism, which uses oxygen to break down various fuels," Brooks said.

Post-doctoral researcher Takeshi Hashimoto and staff research associate Rajaa Hussien established this by labeling and showing colocalization of three critical pieces of the lactate pathway: the lactate transporter protein; the enzyme lactate dehydrogenase, which catalyzes the first step in the conversion of lactate into energy; and mitochondrial cytochrome oxidase, the protein complex where oxygen is used. Peering at skeletal muscle cells through a confocal microscope, the two scientists saw these proteins sitting together inside the mitochondria, attached to the mitochondrial membrane, proving that the "intracellular lactate shuttle" is directly connected to the enzymes in the mitochondria that burn lactate with oxygen.

"Our findings can help athletes and trainers design training regimens and also avoid overtrai
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Source:University of California - Berkeley

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