Abstract
Previous experiments (external application of sap, perfusion of vacuole with sea water 1 , 2 ) have indicated that the large bio-electric potential (P.D. = 70 to 80 mv. outside +) across the protoplasm of impaled Halicystis cells (coenocytic marine alga) is mostly independent of inorganic ions or other gradients between cell sap and environment. Internal gradients or assymetries in the protoplasmic film itself were suggested. Since the P.D. can produce a measurable current for long periods through a completed circuit, a source of energy, eventually metabolic, must be available. Experiments have therefore been directed toward analyzing the relation between P.D. and metabolism in this organism. The electrical methods are those previously employed, 1 , 2 the cells being kept in the dark to avoid photosynthesis. Manometric measurements of O2 consumption by the Warburg method were made on groups of several intact cells under comparable conditions (except for impalement). Concurrent P.D. and respiration measurements on identical impaled cells are now under way.
Oxygen tension. Over the range where respiration is unchanged, the P.D. is also unaltered. This holds for pure O2, air, and for mixtures of O2 with N2 down to about 2% O2, brought into equilibrium with sea water by continued bubbling. If bubbling of the 2% O2 mixture is stopped, the P.D. drifts downward as O2 is consumed in the vicinity of the cell, eventually falling to 10 or 15 mv. +. Stirring of the sea water, or rebubbling of 2% O2 promptly restores the P.D. This downward drift and recovery may be repeated almost indefinitely. Further lowering of O2 tension, e. g., to 0.2% O2 in N2, reduces the P.D. to 10 mv. or less while bubbling or stirring continues. Respiration also falls to low values in this mixture.
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