AbstractK+‐sensitive liquid ion exchange electrode systems respond with a slow potential change to acetylcholine, choline, anticholinergic drugs, biogenic amines, and glutamic acid. The response threshold has been defined, and in most cases it is at extremely low concentrations (10−7–10−;5M). The direction of the potential change varies, but in most instances it is additive to that produced by external K+. The K+electrode system is further sensitive to decreasing pH, within a narrow and possibly physiological range of pH. These findings suggest that small measured changes in extracellular K+are biased by the chemosensitivity of the liquid ion exchange electrode system to some compounds of physiological imp