Intracellular pH in hypoxic smooth muscle.

Hypoxia impairs contractility in canine tracheal smooth muscle (TSM). This is attributed to intracellular lactacidosis. The present studies were undertaken to confirm this. Lactate was found to be significantly increased in hypoxic TSM (65.36 +/- 7.37 mg/100 g wet tissue), compared to normoxic (29.83 +/- 5.05). Intracellular pH (pHi) was, however, significantly increased in hypoxic active TSM to 7.71 +/- 0.05 as compared to 7.30 +/- 0.03 in normoxic active muscle. pHi of resting normoxic muscle (7.20 +/- 0.04) was statistically not different from that of resting hypoxic muscle. The pHi's of resting normoxic and active hypoxic muscles were significantly different. These results show that under in vitro, hypoxic conditions: 1) an increase in glycolysis in TSM is indicated by the increased lactate production, 2) there is a surprising, concomitant rise in pHi rather than a decrease as previously expected, and 3) it is mechanical activity of the muscle which leads to this paradoxical result, inasmuch as pHi is unaltered in the resting hypoxic muscle.