3. CELLULAR ASPECTS OF ACTIVE TRANSPORT
193
(b) The other approach deals essentially with attempts to identify
some cellular extractable material with the molecular architecture responsible for some of the permeability characteristics of the membrane.
There are interesting attempts to isolate and identify the structure
involved in the permeability of cellular membranes.
Chagas (232, 233) in Rio de Janeiro and Ehrenpreis (234, 235) in
Nachmansohn's laboratory in New York have claimed to have isolated
the acetylcholine receptor from the electric organ of Electrophorus
electriaus L.
Woolley (236) has also tried to isolate a receptor reacting with
5-hydroxytryptamine in the presence of Ca. Beumer (237) extracted from
Shigella substances able to combine with phages in the same way as
the intact bacterial cell, in that both have the same requirements in Na
and Ca for maximum binding. Hokin et al. (238) propose phosphatidic
acid as the sodium carrier.
On the basis of the results published by the above authors, it appears
to be very difficult to ascribe a well-defined physiological role to the
material extracted. Some important properties found with the intact cell
cannot always be demonstrated on the extract. In the case of the socalled acetylcholine receptor, curare binding could not be significantly
reduced in the presence of carbamylcholine, a type of competition well
demonstrated in various in vivo systems.
We have also found that material extracted, according to the technique of Ehrenpreis, from nonconducting tissues (gills of crab, red cells)
(unpublished results) possesses at least some of the properties already
described for the protein(s) isolated by Ehrenpreis. These results must
therefore be interpreted with the greatest caution, until we have more
criteria available, before deciding that an extract might be of physiological significance in cellular permeability (239).
IX. Conclusions
We are just beginning to have some indication of the possible relationships existing between the various functions of a membrane as well
as their connection with the general metabolism of the cell.
Thus it seems reasonable to assume that the active transport of
cations is essentially devoted to the regulation of cell volume. That we
are dealing with a very primitive cellular function seems to be indicated
by the fact that the active transport of cations is possible in the absence
of amino acids, sugars, and fatty acids, while the converse is not verified.
In this context, it could hardly be suggested that the ionic composition
of the intracellular phase, i.e., a medium rich in potassium and poor in
sodium, is an adaptation to the impelling necessity of enzymatic activity.
193
(b) The other approach deals essentially with attempts to identify
some cellular extractable material with the molecular architecture responsible for some of the permeability characteristics of the membrane.
There are interesting attempts to isolate and identify the structure
involved in the permeability of cellular membranes.
Chagas (232, 233) in Rio de Janeiro and Ehrenpreis (234, 235) in
Nachmansohn's laboratory in New York have claimed to have isolated
the acetylcholine receptor from the electric organ of Electrophorus
electriaus L.
Woolley (236) has also tried to isolate a receptor reacting with
5-hydroxytryptamine in the presence of Ca. Beumer (237) extracted from
Shigella substances able to combine with phages in the same way as
the intact bacterial cell, in that both have the same requirements in Na
and Ca for maximum binding. Hokin et al. (238) propose phosphatidic
acid as the sodium carrier.
On the basis of the results published by the above authors, it appears
to be very difficult to ascribe a well-defined physiological role to the
material extracted. Some important properties found with the intact cell
cannot always be demonstrated on the extract. In the case of the socalled acetylcholine receptor, curare binding could not be significantly
reduced in the presence of carbamylcholine, a type of competition well
demonstrated in various in vivo systems.
We have also found that material extracted, according to the technique of Ehrenpreis, from nonconducting tissues (gills of crab, red cells)
(unpublished results) possesses at least some of the properties already
described for the protein(s) isolated by Ehrenpreis. These results must
therefore be interpreted with the greatest caution, until we have more
criteria available, before deciding that an extract might be of physiological significance in cellular permeability (239).
IX. Conclusions
We are just beginning to have some indication of the possible relationships existing between the various functions of a membrane as well
as their connection with the general metabolism of the cell.
Thus it seems reasonable to assume that the active transport of
cations is essentially devoted to the regulation of cell volume. That we
are dealing with a very primitive cellular function seems to be indicated
by the fact that the active transport of cations is possible in the absence
of amino acids, sugars, and fatty acids, while the converse is not verified.
In this context, it could hardly be suggested that the ionic composition
of the intracellular phase, i.e., a medium rich in potassium and poor in
sodium, is an adaptation to the impelling necessity of enzymatic activity.