Arsenazo III Signals Following Action Potential as Influenced by Nitrate in Xenopus Skeletal Muscle

Arsenazo III was injected into a Xenopus skeletal muscle fiber to measure the changes in myoplasmic free Ca2+ concentration following an action potential. The arsenazo III signal started to rise after a latent period of 2.4msec, attained its peak at another 5.0msec and then decayed exponentially with a half time of 15.6msec, at 22-24°C. Nitrate ions prolonged the falling phase with a slight increase in the peak amplitude. It is suggested that nitrate produces continuous Ca release as well as augmentation of the initial burst of Ca release in highly stretched muscle fibers.