Influence of chloride ions on changes in membrane potential during prolonged application of carbachol to frog skeletal muscle

1 Micro‐electrodes were used to follow changes in the membrane potential at the end‐plate region of single fibres in narrow strips of frog skeletal muscle exposed to carbachol applied in continuously flowing Ringer solution containing tetrodotoxin (200 nm) and neostigmine (3 μm). 2 The depolarizations elicited by carbachol (5–20 μm) usually developed in two phases, the first of which was generally complete within 30 s whereas several min were required for the second. 3 Repolarization after carbachol also occurred in two phases, the second of which outlasted the time needed to clear the bath, and varied with the magnitude and duration of the depolarization which carbachol had caused. 4 These findings could best be explained in terms of the consequences of net entry of chloride ions into the fibre during the depolarization caused by carbachol. This hypothesis is supported by three lines of evidence:

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