The Suitability of the antimony electrode for pH determinations in mammalian heart

Abstract

Antimony electrode provides a stable and reproducible means for the determination of intramuscular pH. Large changes in bicarbonate or phosphate concentrations are required before a significant alteration in electrode response is observed and thus is quite suitable for physiological measurements. However, dramatic shift in mv- pH relationship for this electrode was seen upon changing pO 2 of the medium. When the electrode was employed to monitor intramuscular pH in isolated perfused rat heart, it was found that Na + or K + free medium produced a severe acidosis ( pH < 6.5) along with loss of contractility. Ca 2+ free perfusion, on the other hand, resulted in a failure of contractility within 30 sec without any change in interstitial pH. Upon stretching the heart when the perfusion rate was maintained at constant level, an increase in both contractile force and pH occurred. Norepinephrine along with increased perfusion flow produced an increase in both rate and force of contraction without any significant change in interstitial pH. However, at constant perfusion rate, the interstitial pH increased dramatically. Similarly, global ischemia resulted in a decline in contractile force and initial increase and subsequent decrease in interstitial pH. No decrease in pH was noted when coronary flow was reduced gradually. These results suggest that the antimony electrode is only suitable in situations which are not associated with larger changes in pO 2.