CALCULATIONS OF BIOELECTRIC POTENTIALS : V. POTENTIALS IN HALICYSTIS

Interest in the study of Halicystis and of Valonia has been stimulated by discoveries of marked contrasts and striking similarities existing side by side. This is illustrated by new experiments with the alkali metals and alkaline earths. In Halicystis the apparent mobilities of K⁺, Rb⁺, Cs⁺, and Li⁺ (calculated by means of Henderson''s equation from changes in P.D. produced by replacing sea water by a mixture of equal parts of sea water and 0.6 M of various chlorides) are as follows, u _K, = 16, u _Rb = 16, u _Cs = 4.4, and u _Li = 0.2; u _Na is taken as 0.2. These values resemble those in Valonia except that in the latter u _Cs is about 0.2. No calculation is made for u _NHNH4, because in these experiments even at low pH so much NH₃ is present that the sign of the P.D. may reverse. This does not happen with Valonia. According to Blinks, NH₄ ⁺ at pH 5 in low concentrations acts like K⁺. The calculation gives u _Mg = 1.9 which is similar to the value found for Valonia. No calculation can be made for CaCl₂ since it produces protoplasmic alterations and in consequence Henderson''s equation does not apply. This differs from Valonia. Evidently these plants agree closely in some aspects of electrical behavior but differ widely in others.     

NATURE OF THE ACTION CURRENT IN NITELLA : III. SOME ADDITIONAL FEATURES

Several forms of the action curve are described which might be accounted for on the ground that the outer protoplasmic surface shows no rapid electrical change. This may be due to the fact that the longitudinal flow of the outgoing current of action is in the protoplasm instead of in the cellulose wall. Hence the action curve has a short period with a single peak which does not reach zero. On this basis we can estimate the P.D. across the inner and outer protoplasmic surfaces separately. These P.D.''s can vary independently. In many cases there are successive action currents with incomplete recovery (with an increase or decrease or no change of magnitude). Some of the records resemble those obtained with nerve (including bursts of action currents and after-positivity).     

EFFECTS OF HYDROXYL ON NEGATIVE AND POSITIVE CELLS OF NITELLA

Remarkable changes are brought about by KOH in transforming negative cells of Nitella (showing dilute solution negative with KOH) to positive cells (showing dilute solution positive with KOH). NaOH is less effective as a transforming agent. This might be explained on the ground that the protoplasm contains an acid (possibly a fatty acid) which makes the cell negative and which is dissolved out more rapidly by KOH than by NaOH, as happens with the fatty acids in ordinary soaps. Part of a negative cell can be changed to positive by exposure to KOH while the untreated portion remains negative. After exposure to KOH the potential the protoplasm has when in contact with NaCl may increase. At the same time there may be an increase in the potassium effect; i.e., in the change of P.D. in a positive direction observed when 0.01 M KCl is replaced by 0.01 M NaCl. In some cases the order of ionic mobilities is u _K > v _OH > u _Na. This shows that the protoplasmic surface cannot be a pore system: for in such a system all cations must have greater mobilities than all anions or vice versa.