Relation of Membrane Properties of the Giant Muscle Fiber of a Barnacle to Internal Ionic Composition

Abstract

Giant muscle fibers 1 to 2 mm in diameter and 4 to 5 cm in length are found in the barnacle Balanus nubilus. The preparation offers an excellent opportunity for studying membrane mechanisms of excitation by controlling the internal ionic composition of the fiber. The internal ionic composition was altered by intracellular injection through a glass pipette longitudinally inserted into the fiber. A test solution of a given ionic composition was injected over the whole length of the fiber until the diameter increased by a factor of 1.5 to 2.0. This should make the internal ionic composition of the treated fiber close to that of the injected solution. The final concentration of K or Na inside each treated fiber was determined by flame photometry after each experiment. The internal C1 concentration was also determined by the mercuric nitrate method. To obtain a given concentration of the internal Ca++ or Mg++ concentration the injection was made with a solution containing EDTA or EGTA and Ca or Mg salts in varying proportions. The resting potential of the fiber decreased approximately linearly with th

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