Sensitivity of the sodium efflux in single barnacle muscle fibers to the microinjection of aluminum

A study has been made of the behavior of the Na efflux in single muscle fibers from the barnacle, Balanus nubilus, toward the microinjection of AlCl 3. The effect of microinjecting AlCl 3 is either biphasic with inhibition following transitory stimulation, or monophasic with inhibition occurring promptly and taking about 1 hr to reach a maximum. The magnitude of the inhibition is dose dependent and the minimally effective concentration is 10 m m. This is diluted by the myoplasm by a factor of roughly 100. Fibers injected with 1 m AlCl 3 are found to be insensitive to 10 −4 m ouabain, whereas fibers injected with 0.5 m AlCl 3 show a further fall in Na efflux, which is smaller than that seen in control fibers. The response of the ouabain-insensitive Na efflux to the injection of 0.5 m AlCl 3 is biphasic: stimulation is followed by inhibition. The stimulatory phase is largely dependent on the presence of external Ca 2+ and is reversed by the sudden omission of Ca 2+ from the bathing medium. Fibers also injected with 0.5 m AlCl 3 show a marked reduction in the response of the Na efflux to high external K. Injection of ATPMg before or after the injection of AlCl 3 fails in most instances to abolish or reverse the inhibitory effect. By contrast, fibers preinjected with deferoxamine show little or no effect following the injection of AlCl 3. However, external application of deferoxamine is ineffective.