"The Permeability of Living Cells"

RESPONSES OF CELLS TO pH CHANGES IN THE MEDIUM

“…Relatively little, however, has been done to investigate conditions in the environment of cells which may more immediately determine or alter their activities. Some of the earlier observations on the response 6f plant and animal cells to changes in hydrogen ion concentration and partial pressures of atmospheric gases have been reviewed by Heilbrunn (7) and by Brooks and Brooks (2).…”

The Relation of External Rubidium Concentration to Amounts and Rates of Uptake by Excised Potato Tuber Tissue.

“…The Freundlich equation is reported to better fit the cases in which the adsorbent is impure or in which a multimolecular layer is adsorbed, whereas the Langmuir equation better fits the cases having a unimolecular layer (7).3 Since the present results with potato discs show con- 3 Ion uptake has been reported in at least one case (10) …”

“…The fact seems well established that the time course of cation uptake consists of at least two, easilv distinguished, time phases: 1) an initial non-metabolic process which is presumed by many to be an adsorption, adsorption-exchange, or exchange process (1, 24,26,28,30,32), and 2) a metabolic process, which is dependent on aerobic respiration and in which accumulation may proceed against a concentration gradient (2, 3,4,17,21,28,36). Phase one of the uptake, or loss, is essentially independent of temperature and aeration as shown by isotopic exchange of potassium (5); it corresponds in exchange to relative concentration of two ions as expected by the law of mass action (36); and it shows ion selectivity (13,22).…”

“…In former years there was a strong tendency to view initial ion penetration as a diffusion and permeability process (3,27); however, more recently a trend has developed to consider the first steps in uptake to be a binding reaction, eg., an ion carrier complex, either in a non-metabolic process or in energetically coupled reactions (27). This view has received subst.ntial support recently with the demonstration that in some cases of related ions the effect of one ion on another in uptake by roots fits the AMichaelis-AMenten equation for competitive inhibition as in an enzymatic process, whereas with other ions uptake is uncompetitive (8,9).…”

The Effects Produced by Diffusion in Aqueous Systems Containing Membranes.

“…Krogh (62) has reviewed numerous cases of the active transport of water and salts between aquatic animals and their environment. 11. DIFFUSION I N BULK SYSTEMS A. Thermodynamic considerations .…”