3. CELLULAR ASPECTS OF ACTIVE TRANSPORT
179
isosmotic intracellular regulation, or from the latter alone. We tentatively
propose to consider the isosmotic intracellular regulation as being the
result of a differential influence of the ionic composition of the cell on
the activity of the biochemical systems responsible for the production of
amino acids, on the one hand, and for their discharge, on the other
hand. As the differential action is lacking in the stenohaline species, a
change in the ionic composition of the cell would only result in a modification of the turnover rate of the amino acid pool, but not of its
concentration.
In vertebrates the intracellular pool of free amino acids seems to be
related to the ionic composition of the intracellular fluid and various
authors have shown that in Κ deficient animals the intracellular content
of cationic amino acids increases
(136-141).
As we have shown, amino acids seem to play an important part in the
osmoregulation of invertebrates. In aquatic or semiaquatic vertebrates
this role seems to belong to urea (142, 143).
VI. Hormones and Permeability Characteristics of Living
Cellular Membranes
A. NEUROHYPOPHYSEAL HORMONES
Two active hormonal substances, secreted by the neurohypophysis
have been isolated and synthesized (144). Both are octapeptides. They
are oxytocin and vasopressin. Two vasopressins are of natural occurrence:
arginine-vasopressin and lysine-vasopressin. Besides its oxytocic action,
oxytocin affects both Na and water flux across the amphibian skin and
the urinary bladder while vasopressin appears to have no activity. The
renal effects are also well known.
More recently another active principle has been isolated from the
neurohypophysis of chicken (145), frog (146), and fish (Gadus luscus
L.) (147). This principle seems to have the same structure as the
arginine-vasotocin synthesized by Katsoyannis and du Vigneaud (148).
As already mentioned, in amphibian skin and urinary bladder neurohypophyseal extracts exert a very marked action on the net flux of water
arising under the influence of an osmotic gradient.
The generally accepted opinion is that the hormone acts on the cellular membrane facing outward (i.e., mucosal side for the bladder), by
increasing the permeability to water and to Na. Calcium plays an important role in this phenomenon since an excess of this ion inhibits the
effect of the hormone (149, 150).
In the light of the behavior of water, before and after application of
the hormone, a simple model membrane has been proposed. The theoretical approach used in Section II of this chapter is based on this model.
179
isosmotic intracellular regulation, or from the latter alone. We tentatively
propose to consider the isosmotic intracellular regulation as being the
result of a differential influence of the ionic composition of the cell on
the activity of the biochemical systems responsible for the production of
amino acids, on the one hand, and for their discharge, on the other
hand. As the differential action is lacking in the stenohaline species, a
change in the ionic composition of the cell would only result in a modification of the turnover rate of the amino acid pool, but not of its
concentration.
In vertebrates the intracellular pool of free amino acids seems to be
related to the ionic composition of the intracellular fluid and various
authors have shown that in Κ deficient animals the intracellular content
of cationic amino acids increases
(136-141).
As we have shown, amino acids seem to play an important part in the
osmoregulation of invertebrates. In aquatic or semiaquatic vertebrates
this role seems to belong to urea (142, 143).
VI. Hormones and Permeability Characteristics of Living
Cellular Membranes
A. NEUROHYPOPHYSEAL HORMONES
Two active hormonal substances, secreted by the neurohypophysis
have been isolated and synthesized (144). Both are octapeptides. They
are oxytocin and vasopressin. Two vasopressins are of natural occurrence:
arginine-vasopressin and lysine-vasopressin. Besides its oxytocic action,
oxytocin affects both Na and water flux across the amphibian skin and
the urinary bladder while vasopressin appears to have no activity. The
renal effects are also well known.
More recently another active principle has been isolated from the
neurohypophysis of chicken (145), frog (146), and fish (Gadus luscus
L.) (147). This principle seems to have the same structure as the
arginine-vasotocin synthesized by Katsoyannis and du Vigneaud (148).
As already mentioned, in amphibian skin and urinary bladder neurohypophyseal extracts exert a very marked action on the net flux of water
arising under the influence of an osmotic gradient.
The generally accepted opinion is that the hormone acts on the cellular membrane facing outward (i.e., mucosal side for the bladder), by
increasing the permeability to water and to Na. Calcium plays an important role in this phenomenon since an excess of this ion inhibits the
effect of the hormone (149, 150).
In the light of the behavior of water, before and after application of
the hormone, a simple model membrane has been proposed. The theoretical approach used in Section II of this chapter is based on this model.