Acute anoxia attenuates sodium‐hydrogen exchange activity in isolated mammalian ventricular myocytes

Abstract

H+ extrusion through sodium-hydrogen exchange (NHE) was studied in isolated rat ventricular myocytes by monitoring pHi recovery (SNARF fluorescence) from an acid load (20 mM NH4Cl prepulse; Hepes- buffered superfusates). Acute anoxia (1mM Na dithionite, 100% N2, 5-8 minutes) reduced resting pHi by ~ 0.2 units, and slowed recovery rate by ~ 60 %. The slowing could not be explained by increased endogenous H+i-generation, or by increased intrinsic intracellular buffering (which did not change). Reoxygenation induced a rapid, apparent rise of pHi (~ 0.2 units), which occurred in the presence of 30μM cariporide (NHE inhibitor), indicating it was independent of NHE. Subsequent removal of cariporide, then permitted additional pHi recovery, demonstrating that anoxic NHE-inhibition was reversed by reoxygenation. In conclusion, anoxia rapidly and reversibly attenuates NHE activity. Acute anoxic sensitivity is likely to contribute to the attenuation of NHE activity reported during myocardial ischaemia. The apparent reoxygenation-induced rise of pHi observed in the absence of NHE activity is the subject of further study.