Croonian Lecture - The active and passive exchanges of inorganic ions through the surfaces of living cells and through living membranes generally

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Abstract
A review of the recent literature (135 references). Large differences in conc. of individual ions between intracellular and extracellular fluids represent "steady states" (not equilibria) in which passive diffusion is opposed by active transport requiring expenditure of energy by the cell. Passive diffusion is demonstrated by capillary endothelium and glomerular syncytium. The "steady state" is demonstrated by plant roots, giant plant cells, marine and fresh-water protozoa, aquatic animals, aquatic and avian eggs, kidney tubules, mammalian intestine, mammalian erythrocytes, cross-striated muscle of frogs and mammals, frog heart, and various other tissues. In systems with active transport, passive diffusion must be slow to prevent excessive energy expenditure in maintaining the steady state. Krogh calculates the permeability coefficient [image] (where v is vol. of cell in ml., s is surface of cell in sq. cm., t is time in hrs., C1 is conc. of ion in cell, Co is conc. of ion in outer fluid, at and ao are the corresponding radioactivities) for the passive diffusion phase from the results of distr. of radioactive ions reported by various workers. Approximate values for P X 106 are: for K+, 2.8 (Tolypellopsis), 0.8 (Nitella), 0.0053 (human erythrocytes), 0.0082 (rabbit erythrocytes), 0.07 (rabbit erythrocytes in vivo), 0.6 (dog erythrocytes in vivo, correlated with low conc. K+ in cells), 13 (rabbit muscle in vivo), 70 (resting rat muscle in vivo), 230 (working rat muscle in vivo); for Na+, 1.7 (Tolypellopsis), 0.09 (Nitella), 1.4 (dog erythrocytes in vivo), 2 (dog erythrocytes in vitro), 10 (rabbit erythrocytes in vitro), 460 (K-deprived rat jnuscle in vivo); for HPO4, 1.5 (frog gastrocnemius). The higher permeability coefficients for Na+ as compared to .K+ support Lundegardhs sparse mosaic theory of scattered N+ and [long dash]valencies which bind ions and occasionally turn around liberating the ions on the other side of the membrane, rather than the pore theory. Procedures that interfere with active transport (0.0002 to 0.004 raM Pb++, 2 to 5 mM CN-, cold, lack of glucose, or O2 want) result in loss of K+ from most cells. 20 tables and further data in text.

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