Intracellular buffering of heart and skeletal muscles during the onset of hypercapnia

Changes in the total CO2 content of tissues were determined in order to characterize variations in intracellular acid-base parameters during the onset of hypercapnia. Within two minutes after an increasement in the CO2 tension of the inspired air of rats, there were large increases in the intracellular bicarbonate concentrations of both cardiac and skeletal muscles. Greater changes occurred in the heart, and its intracellular pH remained near normal during the first hour of hypercapnia; whereas there was an intracellular acidosis in skeletal muscle. This greater capacity of the heart to buffer excess CO2 has been linked to an increased movement of bicarbonate ions into and/or hydrogen ions out of cardiac cells during hypercapnia (Lai et al., 1973c). Yet, the buffer capacity of the heart was not compromised by metabolic acidosis during which there was a greatly reduced extracellular bicarbonate ion concentration and a greatly increased extracellular hydrogen ion concentration. The intracellular pH of the cardiac ventricle was stable following the imposition of a noncarbonic acid load on normocapnic rats.