The Intracellular Concentration and Activity of Sodium in Giant Barnacle Muscle Fibers

Dear Sir: The existence of sodium binding or compartmentalization in single muscle fibers from giant barnacles was the basis for two recent letters in this Journal (McLaughlin, 1968; Brinley, 1968 b). Evidence for sodium binding from this laboratory is criticized by Brinley (1968 a, see Discussion) because our analytic value for total internal sodium concentration is higher than values obtained in other laboratories (Hagiwara et al., 1964; Beaugd and Sjodin, 1967; Brinley, 1968 a). These laboratories apparently obtained barnacles from Monterey Bay, Calif. (Pacific Biomarine Supply Co.), whereas our laboratory obtained barnacles from local waters. To determine whether this discrepancy is real, we analyzed fibers from California barnacles by our chemical and electrochemical methods. Before chemical analysis, single fibers were soaked for either 30 sec or 10 rain in an isotonic wash solution (655 mM sucrose, 25 mM Tris NOa, 20 mM Ca (NO3)~, 10 na~ Mg (NO3)~). The short wash should remove primarily surface ions while the long wash should remove all the extraceUular ions without depleting the intracellular ions (the myoplasmic sodium activity did not change significantly during the 10 min wash). Extracellular space was determined on companion fibers by a chloride washout method (Gayton and Hinke, 1968). In these barnacles the average extracellular space was 6.1% of fiber water. When corrected for extraceUular ion content, the 30 sec washed fibers yielded results similar to those for the 10 rain washed fibers. The table lists these results (1) together with previous data from this (5, 6) and other (2--4) laboratories. The earliest paper of McLaughlin and Hinke (1966) is not ineluded because no account was taken of extraceUular space in that paper. Our values for sodium, potassium, and chloride concentration for fibers from California barnacles are in good agreement with those obtained by others using barnacles from the same source. Therefore our analytic techniques could not have introduced the discrepancy in sodium concentration between California and Vancouver barnacles. This discrepancy must be real. The variation in internal sodium concentration could be due to differences in species, environment, age, or size. Brinley (1968 a) has shown that species variation is probably not an important factor. Short-term environmental differences can also be ruled out because the California barnacles maintained the same ionic content for up to 2 wk in our aerated seawater.