INFORMATION
Transport
THE BASICS
WHAT IS PASSIVE
TRANSPORT?
Transport is used to move particles in and out of a cell through their membrane, and this is done in one of two ways- passive or active transport. Passive transport is the simpler form of transport of the two. It is the random movement of particles filling a space from high to low concentration. Only small, nonpolar particles are able to move across the cell membrane in this way because their transport does not require ATP energy.
In special cases, some particles must be moved through a protein. This is called facilitated diffusion, and is also how glucose moves into cells. Water moves into cells through facilitated diffusion as well. During a process called Osmosis, water moves in bulk through a protein called aquaporin. This is responsible for all of the water in our body, which we would be unable to survive without.
Patients with MS have been found to be deficient in vitamin A, which is regularly uptaken in the human body through diffusion and considered essential. Vitamin A assists in the regeneration of plasticity in the central nervous system and enters the cell membrane through diffusion. Vitamin A deficiency causes dysregulation of immune tolerance and pathogenic immune cell reproduction, which is all linked to speeding up neurodegeneration of patients with MS. Vitamin A is small and nonpolar, so it is able to move easily across the cell membrane and into the body, which is why it is such a standard and crucial vitamin.
Image credit: OpenStax
This photo shows the passive transport of water through Osmosis. In the before image there was an unequal concentration of water between both sides of the tank, and the second picture showed how the high concentrations of water moved into low concentrations in order to achieve equilibrium.
Image credit: OpenStax
The photo shows facilitated diffusion in the cell membrane. A protein channel, also known as an integral protein, sits in the bilayer of the cell membrane and allows for outside particles to move in from high to low concentration.
THE BASICS
WHAT IS ACTIVE
TRANSPORT?
Image credit: ResearchGate
This diagram shows the movement of exocytosis. Molecules move into a cell and gather inside of a vesicle, and are then able to escape through non-vesicle related secretion, or moving into late endosomes and lysosomes that digest and release waste.
Active transport is much more complex than passive transport. It moves large, charged particles into the cell membrane, and to do this, it requires ATP energy. Transport proteins must be used to do this, and ATP energy assists in forming the shape of the proteins in order to fit the large particles moving in. Contrary to passive transport, active transport only moves molecules from low to high concentration.
Through active transport, masses of molecules can enter and exit a cell. They do this through processes called endocytosis and exocytosis. When a vesicle fuses with a cell membrane, it releases material from a cell, also known as the active transport process exocytosis. Exocytosis can release hormones into the bloodstream and release waste from the cell, thus detoxifying a cell while regulating hormones.
In one of the most common types of active transport, the Sodium Potassium Pump (SaK pump), nerve impulses travel throughout your body. The SaK pump is a specialized transport, or integral, protein found in the cell membrane. It moves potassium ions into the cell, while also moving sodium ions out of the cell to create a gradient of both sodium and potassium ions. Said gradients are then used to transmit electrical signals along nerves, which is what allows them to function. Since the SaK pump is heavily focused in the central nervous system, it plays a significant role in multiple sclerosis. In MS, there is a disruption in the axonal transport on the sodium potassium pump which stops transmitting nerve signals. As the nerve signals lose their connection between each other, communication is lost and the nerves fail.
This photo shows the process of active transport and the sodium potassium pump. Low concentrations of potassium move through transport proteins into areas of high concentration, while sodium moves out of the membrane from low to high concentration. Attached to each protein is an ATP molecule that is changing the shape/function of the protein.
Image credit: KhanAcademy
INFORMATION
Transport
Proteins Involved
IN MULTIPLE SCLEROSIS
Aquaporin
Aquaporin, an integral transport protein, plays a specific role in fighting against MS. Aquaporin is a channel protein that moves water in bulk into the cell membrane. Aquaporin channels and KIR4.1 channels work together to regulate astrocytic functions vital for myelination. With failed astrocytic functions brings failure in myelination, which exposes nerve fibers to potential harm. Failure in other astrocytic functions, like axonal guidance, changes the direction of nerve signals, and flawed synaptic support breaks communication between a neuron and its target cell.
*astrocytic functions are functions related to astrocyte cells. astrocytes are found within the central nervous system and preform axonal guidance and synaptic support. They also have control over the blood brain barrier and productive blood flow.*
KIR4.1 Channel
The KIR4.1 channel is an ATP-sensitive potassium channel found in the astrocyte membrane in most MS patients. KIR4.1 works with aquaporin water channels to maintain crucial astrocytic functions in a neuron that help to build myelination. A recent study from Chen Gu of Ohio State University shows that antibodies have been detected fighting against KIR4.1 in patients with MS (Chen Gu, 2016). This hinders myelination and all other astrocytic functions that are fundamental for nerves.
Image credit: OpenStax
This picture shows the basic layout of a neuron, or nerve cell. The star-like head is the astrocyte that holds the nucleus, and is therefore the command center of the cell. The astrocyte branches off with an axon nerve that is covered and protected by myelin sheaths. Oligodendrocytes sit off of the myelin sheaths, and are responsible for building up said myelin.
Sodium Potassium Pump
The sodium potassium pump protein is responsible for sending out electrical signals in nerves. It moves sodium ions out of cells from low concentration to high concentration, and potassium ions into the cell through low to high concentration as well. This process builds up the nerve impulses that allow neurons to communicate, thus giving function to our entire body. In MS, the pump goes defective and causes for nerve signals to be broken apart. This is what brings upon flawed movement, balance, vision, and sensory- the debilitating symptoms of the disease.