The Relationship Between Sodium, Potassium, and Chloride in Amphibian Muscle

Abstract

In a previous publication (28) it was shown that the cells of the sartorius muscle of the toad Bufo marinus were able to maintain their internal K + at an absolute level despite great fluctuations (0 to 25 m.eq. per liter) of the external K +. When the external level was raised to 50 m.eq. per liter there was an intracellular increase amounting to about 17 per cent of the control level in normal Ringer. This is in contrast to the capacity of the cell to maintain an absolute ratio Na+ou~/Na+m of approximately 3:1 in the face of large variations in the external Na + (45 to 650 m.eq. per liter).Boyle and Conway (2) had shown that K + entered the cell in proportion to the increase in external K +, from which they drew the conclusion that the intracellular K + content would result from the electrochemical gradient, the product K+m X CI-~, being equal to the product K+o~t X Cl-ou~.In this paper it is our intention to correlate the changes in the intracellular Na + and K + content brought about by alterations in the external ionic environment with the concomitant movements in chloride ion.A bibliography of the earlier literature relating to the estimation of chloride in muscle has been given by Fenn (9). We shall refer later to the work of Carey and Conway (3), Levi and Ussing (18), and Harris and Martins-Ferreira (10).The method of estimation of chloride employed by some of the earlier workers (the Van Slyke acid digest), has been shown by Heilbrunn and Hamilton (11) and Wilde (34) to yield results up to 30 per cent too low. The methods used by us for the estimation of Na +, K +, and CI-were such that all three ions could be estimated on the same muscle. This has not been possible with previous methods.The movements of Na + and C1-are so closely linked that we have formed a tentative hypothesis that these ions exist together in an intracellular phase. The amounts of the two ions in this phase are usually equivalent, and depend on the concentration of the same ion in the external medium. The amount of * This work was undertaken with the aid of a grant from the

Osmotic responses demonstrating the extracellular character of the sarcoplasmic reticulum

“…The absolute volumes as calculated from our data and as predicted of course agree at normal osmotic pressure since they were taken in both cases to be the same, namely 13 % of cell volume. At 3x5 x N osmotic pressure the predicted volume is (Steinbach, 1947;Simon, Shaw, Bennett & Muller, 1957) (Frazini-Armstrong & Porter, 1964;Huxley, 1964;Page, 1964;Birks, 1965) and it appears unlikely that any element of the sarcoplasmic reticulum itself is open to extracellular fluid at the sarcolemma. Thus the most likely site for extracellular fluid to gain access to the sarcoplasmic reticulum is at the region of contact between the transverse tubules and the triad sacs.…”

“…It is of considerable interest with regard to this hypothesis that studies on the distribution of electrolytes in frog skeletal muscle have consistently revealed a discrepancy between the actual measured intracellular ion concentrations and the concentrations which are predicted for muscle by the Donnan equilibrium. To explain this discrepancy a number of workers (Steinbach, 1947;Simon, Shaw, Bennett & Muller, 1957) have postulated the existence of a small intra-fibre compartment accessible to all extracellular ions. Harris (1963) on the basis of studies on the distribution of muscle chloride, calculated that for the Donnan equilibrium to hold, this space must contain 15 % of the total cell water (about 12 % of cell volume), a figure in remarkable agreement with the volume of the sarcoplasmic reticulum as measured by Peachey (1965), and considered as a possible location for this space by Harris.…”

Ionic interactions in acetylcholine contraction of the denervated rat diaphragm

“…The initial loss of extracellular Na+ would reduce this gradient, which would tend to be restored 'by a later loss of intracellular Na+ (Simon, Shaw, Bennett & Muller, 1957). Some evidence for this hypothesis is derived from the observation that the restitution of extracellular Na+ brought about an initial increase in the ACh response to greater than normal levels; one would expect the Na+ gradient to be temporarily increased.…”

“…It is possible that the partial restoration of tension which was occasionally seen after prolonged exposure to low Na+ or Na+-free solution maybe related to the partial dependence of the ACh contraction on the Na+ gradient across the membrane. The initial loss of extracellular Na+ would reduce this gradient, which would tend to be restored 'by a later loss of intracellular Na+ (Simon, Shaw, Bennett & Muller, 1957). Some evidence for this hypothesis is derived from the observation that the restitution of extracellular Na+ brought about an initial increase in the ACh response to Effect of Na+ depletion on the ACh contraction of denervated diaphragm.…”

Some Observations Concerning the End-Plate Potential

“…This phenomenon did not happen in all muscles, but tended to take place in muscles with low resting potentials. One factor for this irregularity may be the great variability of Na content in the muscle (Simon, Shaw, Bennett & Muller, 1957). The time course of the reversed e.p.p.…”