Intracellular pH in sheep Purkinje fibres and ferret papillary muscles during hypoxia and recovery.

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1. The changes of intracellular pH (pHi) of papillary muscles from ferret and Purkinje fibres from sheep heart during hypoxia and recovery from hypoxia were recorded with pH-sensitive micro-electrodes filled with neutral H+ carrier. 2. Hypoxia was produced by replacement of O2 with N2 in the superfusing solutions. When oxidative phosphorylation was prevented, developed tension fell within 20 min to about 16 and 21% of its control value for papillary muscle and Purkinje fibres respectively. On restoration of O2, recovery of developed tension in ferret papillary muscle is preceded by a transient additional decrease. 3. In ferret papillary muscle, the pHi first increased by a mean value of 0.11 pH units after 3 min hypoxia, then decreased by about 0.24 pH units after 20 min. In sheep Purkinje fibres, the initial alkalosis was small or absent, and after 5-9 min, the pHi started to fall reaching 0.17 pH units after 20 min of hypoxia. On return to oxygenated solution, a transient additional intracellular acidification occurred. This acidification reached its peak of 0.31 pH units in papillary muscle and of 0.13 pH units in Purkinje fibres. In both preparations hypoxia was accompanied by a depolarization of a few millivolts. 4. The presence of cyanide (1-2 mM) or fluorodinitrobenzene (20-40 microM) prevented the additional intracellular acidification occurring on return to oxygenated solution. Removal of cyanide itself produced a transient but smaller and slower acidification. 5. On both preparations, exposure to a Tyrode solution containing 10 mM-L-lactate produced a transient intracellular acidification. After recovery from this acidification the acidification produced by hypoxia was increased without affecting the extra acidification on reintroduction of O2. 6. After reduction of the rate of glycolysis by removal of glucose and application of 2-deoxyglucose, the transient intracellular acidification, occurring on return to oxygenated solution after hypoxia, was inhibited in both preparations. In ferret papillary muscle, insulin (100 mU/ml) potentiated the changes of pHi occurring during hypoxia. 7. Using Na+-sensitive glass micro-electrodes it was found that the intracellular Na+ activity rose slightly during the later stages of hypoxia and rose transiently on readdition of O2. These results are consistent with a Na+-H+ exchange being stimulated by acidosis. 8. The origins of the pH changes during and after hypoxia are discussed as are the differences between the responses of sheep Purkinje fibres and ferret papillary muscle.

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