Effects of Temperature on Arsenazo III Ca2+-transients in Xenopus Skeletal Muscle Fibers
Arsenazo III (AZ), a Ca2+ indicator dye, was injected iontophoretically into Xenopus skeletal muscle fibers. AZ Ca2+-transients (AZ signals) following action potentials were measured by a pair of photomultipliers at the wavelength of 651-721 nm. As the temperature was lowered, the latency of the AZ signal (T1), the time to peak (T2) and the decay time constant (T3) were prolonged. The values of T1, T2 and T3 were about 1.5, 4 and 25 msec at 20-21°C and about 5, 10 and 80 msec at 7°C. An Arrhenius plot for T2 and T3 indicated that the values of Q10 for T2 and for T3 were 1.7 and 2.2. It was suggested that, at low temperatures, the dissociation of Ca from Ca-binding proteins appears to be the rate limiting factor of the falling phase of the AZ signal.