Evidence for the Heterogeneous Distribution of Chloride in the Barnacle Muscle

The kinetics of 36Cl− exchange and the outflow of fiber Cl− into a bath solution of low Cl concentration were studied in single striated muscle fibers of the giant barnacle. The results indicate that the intrafiber Cl− can be divided about equally between a rapidly exchanging fraction which is free in the myoplasm and a slowly exchanging fraction which is either bound or compartmentalized. Furthermore, the free myoplasm Cl− fraction appears to be excluded from about 45% of the intrafiber water. These findings are further evidence in favor of a heterogeneous distribution of water and monovalent inorganic ions in the barnacle muscle.