Intracellular pH and bicarbonate concentration as determined in biopsy samples from the quadriceps muscle of man at rest.

1. A method for measuring intracellular pH and bicarbonate concentration of human muscle is described. 2. Muscle biopsies from the quadriceps muscle of 13 healthy subjects at rest were analysed for acid-labile carbon dioxide and volume of extra- and intra-cellular water. Extracellular water volume was estimated from the chloride content and intracellular water volume from the potassium content, or alternatively derived from the sample weight. 3. The measured total carbon dioxide content in muscle was 9-84+/-1-39 mmol/kg. 4. Assuming a normal membrane potential (88 mV) and PCO2 of muscle equal to venous blood, calculated intracellular pH was 7-00+/-0-06 and intracellular bicarbonate concentration was 10-2+/-1-2 mmol/l of water.