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Aerobically generated CO 2 stored during early exercise

1999; American Physiological Society; Volume: 87; Issue: 3 Linguagem: Inglês

10.1152/jappl.1999.87.3.1048

8750-7587

Ming‐Lung Chuang, Hua Ting, Toshihiro Otsuka, Xing‐Guo Sun, Frank Chiu, W. L. Beaver, James E. Hansen, David A. Lewis, Karlman Wasserman,

Muscle metabolism and nutrition

Previous studies have shown that a metabolic alkalosis develops in the muscle during early exercise. This has been linked to phosphocreatine hydrolysis. Over a similar time frame, the femoral vein blood pH and plasma K + and[Formula: see text] concentrations increase without an increase in [Formula: see text]. Thus CO 2 from aerobic metabolism is converted to [Formula: see text] rather than being eliminated by the lungs. The purpose of this study was to quantify the increase in early CO 2 stores and the component due to the exercise-induced metabolic alkalosis (E-I Alk). To avoid masking the increase in CO 2 stores by CO 2 released as[Formula: see text] buffers lactic acid, the transient increase in CO 2 stores was measured only for work rates (WRs) below the lactic acidosis threshold (LAT). The increase in CO 2 stores was evident at the airway starting at ∼15 s; the increase reached a peak at ∼60 s and was complete by ∼3 min of exercise. The increase in CO 2 stores was greater, but the kinetics were unaffected at the higher WR. Three components of the change in aerobically generated CO 2 stores were considered relevant: the carbamate component of the Haldane effect, the increase in CO 2 stores due to increase in tissue [Formula: see text], and the E-I Alk. The Haldane effect was calculated to be ∼5%. Physically dissolved CO 2 in the tissues was ∼30% of the store increase. The remaining E-I Alk CO 2 stores averaged 61 and 68% for 60 and 80% LAT WRs, respectively. The kinetics of O 2 uptake correlated with the time course of the increase in CO 2 stores; the size of the O 2 deficit correlated with the size of the E-I Alk component of the CO 2 stores. We conclude that a major component of the aerobically generated increase in CO 2 stores is the new[Formula: see text] generated as phosphocreatine is converted to creatine.