Hypoxia-induced Intracellular Acidification in Isolated Sheep Heart Purkinje Fibres and the Effects of Temperature

The changes of intracellular pH (pH1) produced by hypoxia in sheep heart Purkinje fibres were studied using liquid ion exchanger-filled microelectrodes. A decrease of temperature from 35°C to 22°C caused an alkalinization of 0.3 pH units. Hypoxia (partial pressure of oxygen < 10 mm Hg) for 20 min induced an acidification of 0.26±0.18 units (n=14) at 35°C. The hypoxia-induced acidification at 22°C was smaller than that at 35°C by approximately 65%. Increasing the buffering capacity of the cells decreased the hypoxic acidification. This could be achieved either by use of high extracellular HEPES concentrations (40 mM) or by the use of bicarbonate buffers. Sodium cinnamate (5 mM) increased the hypoxic acidification and slowed the pH1 recovery on reintroduction of oxygen, implying an importance role for lactate flux in pH regulation during hypoxia.