Acetylcholine reduces the slow calcium current in embryonic skeletal muscle cells in culture

Xenopus skeletal muscle cells when grown in culture develop a slow inward calcium current that is sensitive to dihydropyridines. Acetylcholine (ACh, 10 M) applied through a puffer pipette caused a large inward current in these cells (at the holding potential) through the nicotinic receptor channels and reduced the inward calcium current (during a step depolarization to 0 mV). After the ACh application was discontinued the holding current rapidly returned to pre-ACh levels (20 s) whereas the calcium current showed a slow, partial recovery to pre-ACh levels. Outward potassium current was also reduced during the application of ACh but recovered completely after ACh was discontinued. The effect of ACh on the calcium current was not mimicked by muscarine (100 M) and was absent when 10 g/ml -bungarotoxin was added to the bath suggesting that the decrease in calcium current was mediated by current through the nicotinic receptor.