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On the Physiology of Amoeboid Movement : IV.--The Action of Magnesium
1 The Marine Biological Laboratory Plymouth
1. Although movement only occurs if Ca or Sr is present the medium, yet Mg and Ba as well are able to prevent the increased permeability and cytolysis seen in pure NaCl. Cerium also has a similar action at very low concentrations, but it very much less effective than Mg.
2. Excess of Mg never causes the marked increase in viscosity seen in the ectoplasm when Ca is in excess. For this and other reasons it seems that inhibition of movement inexcess Ca is due to direct action on the contractile mechanism, and is not simply the result of decreased permeability.
3. This is borne out by the fact that good movement occurs in mixtures of (MgCl2 + CaCl2) alone, and over a far greater range of concentrations than occurs in mixtures of (NaCl + CaCl2). This can be readily explained by assuming that Mg reduces the permeability of the cell so far that Ca can neither penetrate nor leave the cell and thereby derange the contractile mechanism.
4. Even in any mixture of (NaCl + CaCl2), or of (MgCl2 + CaCl2), movement gradually falls off. Only when all four cations of sea-water are present is movement normal indefinitely : fully normal permeability is maintained only under these circumstances.
5. Since the addition of Mg and K to a solution of (NaCl + CaCl2) not only establishes the normal degree of impermeability but also enormously increases the absolute velocity of movement, it seems probable that the same mechanism which controls permeability is also a part of the whole mechanism of amoeboid movement.
6. The relation of the action of ions to the chemical structure of protoplasm is discussed.
Revised on January 6, 1926
