Effects of pH and uranyl ions on action potential generation and acetylcholine sensitivity of skeletal muscle

Abstract

Over the range pH 9.0–5.2 only a pH below 6 affected action potential generation. The effects were principally an elevation of the depolarization level at which an action potential was triggered and a reduction in the rate of rise of the spike. The acetylcholine sensitivity of the muscle membrane was progressively reduced below pH 6.5 and at pH 5.2 it was only 10% of its value at pH 7. The effects of pH alteration were maximal within 60 sec and were completely reversible. Uranyl ions (0.2–0.4 mM) increased the threshold for action potential generation and depressed the rate of rise of the spike. At a concentration of 0.2 mM the sensitivity of the membrane to acetylcholine was reduced to about 15% of the control level. The similar effect of pH alteration on action potential generation and acetylcholine sensitivity suggests that the membrane structures responsible for these two processes have a similar pK value. The finding that uranyl ions depressed both mechanisms indicates that these membrane structures are phosphate-containing macromolecules.