Mechanisms of intracellular ph recovery from nh4cl-induced acidosis
in anoxic isolated turtle heart: a 31p-nmr study.
Shi, H., P. H. Hamm, R. S. Meyers, R. G. Lawler, and D. C. Jackson.
Departments of Physiology and Chemistry, Brown University,
Providence, RI and Department of Biology, Skidmore College, Saratoga
Springs, NY
APStracts 3:0251R, 1996.
Mechanisms of intracellular pH (pHi) recovery from NH4Cl-induced
acidosis were investigated on isolated perfused hearts of the turtle,
Chrysemys picta bellii, using 31P nuclear magnetic resonance (NMR)
spectroscopy at 20oC. A major goal was to assess the activity of
these mechanisms under anoxic conditions. Based on calculated buffer
capacity and a pHi recovery range at 20oC of 6.75 to 6.95 (normal pHi
7.2-7.4), mean H+ efflux rate during perfusion with CO2 free TES
-buffered Ringer's was only 15% (normoxia) and 25% (anoxia) of that
with HCO3--buffered Ringer's. With HCO3- solution anoxic H+ efflux
rate was about 50% of normoxia (0.333 vs. 0.645 mmol x [lambda]-1 x
min-1), but in TES solution, H+ efflux rate was unaffected by anoxia.
To further characterize the transporters, we used blockers (the Na+
-H+ antiport inhibitor EIPA and the anion exchanger inhibitor DIDS),
ion substitution, and temperature change. EIPA (10[mu]M) inhibited H+
efflux rate by 40% in anoxic TES solution; DIDS (0.5 mM) blocked H+
efflux rate by 85% in anoxic HCO3- solution. No pHi recovery was
observed in either normoxic or anoxic Na+ free solutions, but normal
recovery was observed in the absence of extracellular Cl-. Recovery
of pHi occurred 2-3 times faster at 30oC than at 20oC. ATP was
unaffected by any manipulation in this study, whereas creatine
phosphate (CP) fell during anoxia and both CP and mechanical
performance changed in parallel to pHi. We conclude that pHi
regulation functions during anoxia, although at a reduced rate, and
that recovery from acidosis is dominated, during both normoxia and
anoxia, by a DIDS-sensitive Na+ and HCO3- dependent mechanism, while
EIPA-sensitive Na+-H+ antiport plays a less important role.
Received 5 April 1996; accepted in final form 18 June 1996.
APS Manuscript Number R195-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96