188
ERNEST SCHOFFENIELS
However, in this condition the skin continuously loses Ca. Bourguet
et al. (196, 197) have therefore reexamined this problem using EDTA
(ethylenediamine tetraacetate). The results obtained are difficult to
interpret in terms of a direct action of Ca on the active transport mechanism. More recently Curran et al. (198) have shown that, in the
presence of EDTA, the conductance of the isolated frog skin increases.
As a result the potential difference and the short-circuited current decreases. They have shown that the outflux of Na, CI, and S0 4 increase,
while the influx of Na remains unchanged. The decrease in short-circuit
current is thus completely explained by the increase in Na efflux. The
results show therefore that the Ca has no effect on the active transport
mechanism for Na. The effects observed can be explained in terms of
an action on the passive permeability characteristics of the cellular
membranes (109).
As far as human erythrocytes are concerned, Kahn (199) has shown
that a decrease in Ca concentration is without effect on the Κ influx
while an increased concentration inhibits, at least partially, the influx
of K. Strontium and magnesium are without effect, thus demonstrating
the specificity of the action.
C. POSSIBLE MECHANISM OF ACTION
A simple way of interpreting the action of alkaline earths is to postulate that they are bound to anionic sites in the membrane to form salt
in equilibrium with the ion. It can be stated that (see also ref. 181)
CaX = Ca
2 + + Χ
2 "
(12)
In the case of a polyvalent electrolyte, e.g., a protein, one has
Ca n P = Ca n _iP
2 " + Ca
2 +
(13)
All these reactions are determined by a constant related to the difference
in free energy and entropy of reactants and products in their standard
state. One may therefore write
_ (Ca*+)(X*-)
K
~
(CaX)
( 1 4
)
where Κ is a dissociation constant.
If we use this simple scheme to interpret the role of cations in the
determination of the passive permeability characteristics of living membranes, we have to postulate that X, the molecular architecture responsible for a permeability characteristic can be in the complex form CaX
or in the dissociated form X
2 ~.
ERNEST SCHOFFENIELS
However, in this condition the skin continuously loses Ca. Bourguet
et al. (196, 197) have therefore reexamined this problem using EDTA
(ethylenediamine tetraacetate). The results obtained are difficult to
interpret in terms of a direct action of Ca on the active transport mechanism. More recently Curran et al. (198) have shown that, in the
presence of EDTA, the conductance of the isolated frog skin increases.
As a result the potential difference and the short-circuited current decreases. They have shown that the outflux of Na, CI, and S0 4 increase,
while the influx of Na remains unchanged. The decrease in short-circuit
current is thus completely explained by the increase in Na efflux. The
results show therefore that the Ca has no effect on the active transport
mechanism for Na. The effects observed can be explained in terms of
an action on the passive permeability characteristics of the cellular
membranes (109).
As far as human erythrocytes are concerned, Kahn (199) has shown
that a decrease in Ca concentration is without effect on the Κ influx
while an increased concentration inhibits, at least partially, the influx
of K. Strontium and magnesium are without effect, thus demonstrating
the specificity of the action.
C. POSSIBLE MECHANISM OF ACTION
A simple way of interpreting the action of alkaline earths is to postulate that they are bound to anionic sites in the membrane to form salt
in equilibrium with the ion. It can be stated that (see also ref. 181)
CaX = Ca
2 + + Χ
2 "
(12)
In the case of a polyvalent electrolyte, e.g., a protein, one has
Ca n P = Ca n _iP
2 " + Ca
2 +
(13)
All these reactions are determined by a constant related to the difference
in free energy and entropy of reactants and products in their standard
state. One may therefore write
_ (Ca*+)(X*-)
K
~
(CaX)
( 1 4
)
where Κ is a dissociation constant.
If we use this simple scheme to interpret the role of cations in the
determination of the passive permeability characteristics of living membranes, we have to postulate that X, the molecular architecture responsible for a permeability characteristic can be in the complex form CaX
or in the dissociated form X
2 ~.