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ERNEST SCHOFFENIELS
One thus wonders why the cell would possess a specialized mechanism to control the cation content of its interior. It has been proposed
that the enzymatic activity of the cell is possible only in a special ionic
environment. While this is certainly the case, the possibility still remains
that this is a secondary adaptation to a situation created by a more
urgent necessity.
Another remarkable property of living cells is indeed their ability
to maintain a constant volume throughout life. As the cell interior contains molecules that cannot go through the membrane, inflow of extracellular solution tends to produce swelling of the cell. Swelling can be
avoided if the cell possesses a rigid membrane or a membrane impermeable to a large fraction of the solutes in the extracellular medium. In the
first solution, adopted by some bacterial and plant cells (85), an intracellular hydrostatic pressure is developed to balance the osmotic inflow
of solution. The second solution, i.e., impermeability of the cell membrane, has never been shown to occur. The only remaining possibility
for solving the problem of swelling is therefore for the membrane to
possess a mechanism regulating its ionic content.
B. ORIGIN OF THE POTENTIAL DIFFERENCE EXISTING ACROSS
MOST LIVING MEMBRANES
While there is still some controversy with regard to the exact nature
of the potential difference existing across a living membrane, it is well
demonstrated that the potential difference is a consequence of the
metabolic activity of the cell.
1. Zeta Potential
Some authors consider that the potential difference is of an electrokinetic nature (^-potential). On this view, the potential difference should
result from the presence of fixed charges in the membrane. Charges of
opposite signs are spatially separated within the membrane owing to the
metabolic activity of the cell. This gives rise to the formation of counterion layers and subsequently a potential difference
(86-88).
2. Oxidoreduction Potential
Another theory about the nature of the transmembrane potential has
been proposed recently (89). It is a reinterpretation of the Lund theory
(90) that transmembrane potentials are primarily oxidoreduction potentials. It is assumed that two oxidation-reduction enzyme systems are
located at the two faces of the cell membrane. They are connected by
transmembrane lipoid substances with conjugated bonds. Electrons are
ERNEST SCHOFFENIELS
One thus wonders why the cell would possess a specialized mechanism to control the cation content of its interior. It has been proposed
that the enzymatic activity of the cell is possible only in a special ionic
environment. While this is certainly the case, the possibility still remains
that this is a secondary adaptation to a situation created by a more
urgent necessity.
Another remarkable property of living cells is indeed their ability
to maintain a constant volume throughout life. As the cell interior contains molecules that cannot go through the membrane, inflow of extracellular solution tends to produce swelling of the cell. Swelling can be
avoided if the cell possesses a rigid membrane or a membrane impermeable to a large fraction of the solutes in the extracellular medium. In the
first solution, adopted by some bacterial and plant cells (85), an intracellular hydrostatic pressure is developed to balance the osmotic inflow
of solution. The second solution, i.e., impermeability of the cell membrane, has never been shown to occur. The only remaining possibility
for solving the problem of swelling is therefore for the membrane to
possess a mechanism regulating its ionic content.
B. ORIGIN OF THE POTENTIAL DIFFERENCE EXISTING ACROSS
MOST LIVING MEMBRANES
While there is still some controversy with regard to the exact nature
of the potential difference existing across a living membrane, it is well
demonstrated that the potential difference is a consequence of the
metabolic activity of the cell.
1. Zeta Potential
Some authors consider that the potential difference is of an electrokinetic nature (^-potential). On this view, the potential difference should
result from the presence of fixed charges in the membrane. Charges of
opposite signs are spatially separated within the membrane owing to the
metabolic activity of the cell. This gives rise to the formation of counterion layers and subsequently a potential difference
(86-88).
2. Oxidoreduction Potential
Another theory about the nature of the transmembrane potential has
been proposed recently (89). It is a reinterpretation of the Lund theory
(90) that transmembrane potentials are primarily oxidoreduction potentials. It is assumed that two oxidation-reduction enzyme systems are
located at the two faces of the cell membrane. They are connected by
transmembrane lipoid substances with conjugated bonds. Electrons are