chem 4 - Explanation of Bicarbonate and Citrate Buffering 1...

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Explanation of Bicarbonate and Citrate Buffering JEP online Journal of Exercise Physiology online Official Journal of The American Society of Exercise Physiologists (ASEP) ISSN 1097-9751 An International Electronic Journal Volume 5 Number 3 August 2002 Commentary BLOOD ACID-BASE BUFFERING: EXPLANATION OF THE EFFECTIVENESS OF BICARBONATE AND CITRATE INGESTION ROBERT A ROBERGS Exercise Physiology Laboratories, Department of Physical Performance and Development, University of New Mexico, Albuquerque, NM ABSTRACT BLOOD ACID-BASE BUFFERING: EXPLANATION OF THE EFFECTIVENESS OF BICARBONATE AND CITRATE INGESTION . Robert A. Robergs . JEP online . 2002;5(3):1-5. There exists confusion in the exercise and sports science community over the function and capacity of the bicarbonate (HCO 3 - ) buffer system, as well as the mechanism of action of citrate ingestion for raising blood bicarbonate and pH. This commentary provides a brief explanation of buffers, and their mechanism of action. Blood buffers must function between a pH range of 7.2 to 7.4, while muscle intracellular buffers must function between pH values of 6.2 to 7.0. Ideally, the pK’ characteristics of a buffer must be close to the pH of the tissue. However, the pK’ values for carbonic acid (H 2 CO 3 ) and HCO 3 - are 3.77 and 10.2, respectively. Despite these values, the bicarbonate system is a good blood buffer for pH values close to 7.4. This pK’ and pH disparity results from the influence of body CO 2 stores on each of H 2 CO 3 and HCO 3 - , effectively altering the pK’ of the system close to 7.4. Increasing blood HCO 3 - increases the buffering capacity of blood, which in turn can improve intense intermittent exercise performance. Citrate does not have a pK’ of an ionizable group that is effective within the range of blood pH. Nevertheless, citrate ingestion can increase blood HCO 3 - and pH. A review of the metabolic fate of citrate reveals that no protons are consumed in citrate catabolism. Thus, the benefit of citrate to blood buffering is based on its minor buffering capacity throughout the range of blood pH, and electrochemical properties that effectively raise blood HCO 3 - and pH though adjustments to the distributions of charged molecules within the intracellular and extracellular spaces. More research is needed for establishing the optimal mix of bicarbonate and citrate that most effectively improves blood proton buffering and intense exercise performance. KEYWORDS: Acidosis, Protons, Carbonic acid, Citrate. INTRODUCTION Due to the confusion over the cellular biochemistry of metabolic acidosis (14), exercise physiologists are often questioned regarding the interpretation and application of this knowledge. This author has recently been 1
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Explanation of Bicarbonate and Citrate Buffering questioned on the buffering of acidosis, with particular emphasis on the role of bicarbonate. For example, there has been concern over the pK’ of carbonic acid (3.77), and why citrate ingestion can increase the blood proton buffering capacity.
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This note was uploaded on 11/30/2009 for the course CHEMISTRY 1100 taught by Professor Smith during the Spring '09 term at Missouri (Mizzou).

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chem 4 - Explanation of Bicarbonate and Citrate Buffering 1...

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