The transport of L-glutamate (Glu) by single muscle fibers of Balanus nubilus was studied by means of internal dialysis in an effort to obtain transport data under well-defined intracellular conditions. It is shown that the method effectively controls the sarcoplasmic amino acid composition and Glu metabolism. It was found that the classic neutral amino acid transport systems are either absent or inactive, while Glu is strongly transported by a single system. Nonsaturable Glu "leak" is small relative to mediated transport. Glu influx under 0-trans conditions obeys simple Michaelis-Menten kinetics and shows simple competition with aspartate. Influx is strictly dependent on external Na. Trans-Na reduces influx, whereas trans-Glu has a small stimulatory effect. The preparation may serve as a general model for muscle Glu transport and can be used for a thorough study of the kinetic mechanism.
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