Kankozha M. K.
The Kazakh National Medical
University named after S. D. Asfendiyarov, Republic of Kazakhstan
The
special features of the structure of erythrocytic membrane
(Survey)
Erythrocyte is the regular element
of the blood, small concave disks containing hemoglobin. As is known, the basic
function of erythrocytes is the transfer of oxygen from the lungs to the tissues
of body, i.e., they carried out the respiratory function of these cells and
high oxygen capacity of the blood. However, besides participation in the
process of respiration, they also participate in the adjustment of acid-base equilibrium;
they adsorb amino acid, lipids from the plasma of the blood, then transfer them
to the tissues and support the isotonicity of the blood and tissues.
The cellular membrane, which passes
oxygen, carbon dioxide, ions and water, performs important role in the
erythrocyte.
The structure of erythrocytic membrane corresponds to the plan of
the structure of all diaphragm structures. The content of polar lipids in the
membranes can be used as the criterion, which characterizes not only the type
of the membrane, but also the type of cells. It was assumed that each type of
the membranes contains only one form of diaphragm protein, but it is at present
proven that the proteins can be different.
The greatest part of the proteins of
erythrocytic membrane is connected with the carbohydrates, so-called
glycoproteins among which glikoforin. Glikoforin which have large quantity of
remainders of sialic acid is responsible for approximately 60% of negative
charge on the surface of erythrocytes. Lipids occupy 75% of entire area of
erythrocytic membrane. Between three represented here forms - neutral,
glycolipids and phospholipids, phospholipids are located in a larger quantity.
Researchers separate two basic
unsaturated acids of erythrocytic membrane - arachidonic and olein, also two
basic saturated - palmitic and stearin. The asymmetry of arrangement on the
membrane is very important both for the proteins, and for the lipids, as the part
or even all reserve of phospholipid can be located in the inner or outer layers
of the membrane. This asymmetric arrangement of fats is formed in the process
of the formation of the membranes.
One of the special features of
erythrocytes is being contained inside rigid protein support from the spektrin-aktin
complexes, which limits the motion of proteins. The form and mechanical
properties of erythrocytes are determined by interaction of spektrin-aktin
complex with different components of the membrane.
As is known, cellular erythrocytic
membrane is not permeated for the majority of polar molecules for averting the
diffusion of the most important metabolites of the cell outside. There is defined
transfer system, which guarantees the process of entering into the cell of the
specific polar substances (for example, glucose) from the environment. This
system of transfer answers after the possibility “of saturation” of process, the
specificity of the transported substances, braking by the specific substances
and by the directivity of the processes of transfer.
Erythrocytic membrane is
characterized by electro neutrality. It highly permeated for the ions of
chlorine and other anionic flows. There are specific differences in the ratio of
potassium and sodium inside, also, out of the cells. For example, the
erythrocytes of man comprise: potassium – 27.2, sodium – 0.12, for the rat – 22.8
and 0.18 respectively. The characteristic property of erythrocytic membrane is
the fact, that it possesses high anionic selectivity for such anions as
oxalate, malate, fumarate, maleate, succinate, glyutarat and others. It is
considered that the mechanisms which supply the income of different substances
differ. Value of anion t.i. the length of hydrocarbon chains - not only reason.
Channels that pass cations and anions are different and localized on the
membrane in the different sections. On the external and internal surface of the
membrane can be located different groups which supply the transfer of diverse
substances.
Another mechanism can be connected
with the presence of the hydrophobic layers of the membranes. This mechanism
limits the displacement of carriers in them and determines the speed of the
penetration of different ions.
There is another supposition
relative to diaphragm mechanisms, which consists in the fact that the
permeability of the membrane of erythrocytes can be determined by interaction
of the components of medium with some diaphragm components. Such substances as propronolol,
valinomycin change cation permeability and contribute to membrane
reconstructions, which concern not only lipids.
The disturbance of a transmembrane
potential difference, which leads to a change in the conformation of the
molecules of biopolymers, can be possible mechanism. It also can lead to
permeability changes.
Changes in the protein and fatty
acid composition of erythrocytic membranes are observed with some illnesses,
which entail a change in the properties of the membrane. For example, with the
muscular dystrophy and some forms of the anemia changes concern of protein composition
and an increase of cholesterol and phospholipids are observed with the ischemic
disease of heart.
Structural reconstructions of
erythrocytic membranes are observed during the adaptation to the high temperature.
In this case the large fragments of the membrane with different lipid
composition can be formed. The activity of the membrane connective proteins
depends on composition and state of lipids, and changes in the lipid layer can
lead to the disturbance of the function of cells.
At present extensive information obtained about the structure of
the erythrocytic membranes of man and different animals within the standard and
under the diverse influences.
List of the literature:
1.Christian de Lyuv «Journey into
the peace of living cell». Moscow. Periodical «Mir». 1987 year, page No. 256.
2. Chernitskiy E.A., Vorobey A.V. «Structure and the function of
the erythrocytic membranes». Minsk.
«Science and technology». 1981 year, page No.213.
3.Lenindzher A. «Molecular bases of
structure and function of cells». Moscow: Periodical «Mir». 1974 year, page No.
957.
4.Schmidt R., Tevs G. «The
physiology of man». Moscow: Periodical «Mir». 1996 year, Tom 2, pages
No.324-642
5.Green N., Staut U., Taylor D «Biology».
Moscow: Periodical «Mir». 1990 year, T.1, pages No.368
6.Lev A.A. «Ionic selectivity of
cellular membranes». Leningrad. Periodical «Science». 1975 year, page No.323.