Intercellular communication can be defined as the conversation between two cells. It is studied under the branch of cell biology, which encompasses the study of cellular organelles and cell signaling. Intercellular as well as intracellular communication both come under cell signaling. Intracellular communication can be defined as the communication that takes place within the cell, for example, the cellular response that occurs in response to molecules present inside the cell.
Cells communicate through chemical signals, these chemical signals are known as ligands. These ligands can only interact with the cell that has the receptor for the particular ligand, this ligand-receptor association provides the specificity to the cell signaling or intracellular communication. There are the following types of intercellular communication that occur between the cell, paracrine, autocrine, endocrine, and cell-to-cell contact signaling.
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Features of Cell Signaling
According to the intercellular communication definition, there are the following characteristic features that define intracellular communication.
Specificity- It is attributed to the high affinity of the signaling molecule (ligand) and the complementary receptor. The complementarity of structure between ligand and receptor binding contributes to the high specificity of the signaling pathway.
Amplification- During intracellular communication, the signal amplifies several folds to generate the response, amplification can be attributed to the cooperative nature of the receptor-ligand association.
Desensitization- Also known as adaption, it is the condition that arises due to continuous binding of the ligand to the receptor. It can result in a lack of response by the cell. To avoid such conditions cells follow feedback regulation, which allows removal of ligand and receptor when needed.
Integration- It can be defined as the ability of the system to receive multiple signals and produce a unified response appropriate to the needs of the cell.
Stages of Intercellular Communication
There are three main stages or steps of communication, they are as follows-
Reception- It refers to receiving the signal via ligand molecule binding to the receptor. Receptor proteins are the molecule that spans through the plasma membrane, this receptor provides a specific binding site for the ligand. The ligand generally undergoes a conformational change, leading to the sequential activation of the protein cascade. Another common method is phosphorylation and dephosphorylation of the intracellular protein.
Transduction- refers to the transfer of the signal from the cell surface to the interior of the cell, it is achieved by activating several proteins via phosphorylation, dephosphorylation. A common method is the production of the secondary messenger. This ensures the amplification of the signal received.
Response- A cell generates the varying type of response according to the need, it includes transcription and translation of protein or inhibits the synthesis of a certain protein, succession or inhibition of cell cycle. The result is the change in the metabolic activity of the cell.
Example of Signals to Which Cell Respond
There are the following examples of the ligand to which a cell respond
Cell surface glycoprotein
Examples of Intercellular Communication
Six basic receptor types can be used as an example of intercellular communication, they are as follows,
G-protein coupled receptor, used in vision transmission, epinephrine metabolism.
Receptor tyrosine kinase, used in cell division and glucose metabolism
Receptor guanylyl cyclase, used in the metabolism of nitric oxide and ROS
Gated ion channels, used in the transmission of nerve impulse
Adhesion receptors used to maintain integrity and development in embryonic stages
Nuclear receptors (steroid receptors), used inactivation and inhibition of transcription of certain proteins.
Types of Intercellular Communication
The intercellular communication types can be categorized into three types: autocrine, paracrine, endocrine signaling, and cell-to-cell contact signaling. This signaling mechanism is used according to the ligand and need of the cell.
It is the signaling pathway that has ligand molecules traveling a short distance to bind to its receptor. It can be defined as the signaling pathway in which cells communicate over a relatively short distance. The important feature of such a signaling pathway is that it allows the cell to be in coordination with other cells neighboring it. One of the most important roles of paracrine signaling is in embryonic development, it is through the pluripotent cell that decides its cell lineage, which it follows to develop specific organs and tissues.
Another most widely studied example is synaptic signaling, which comes under as a type of paracrine signaling.
Synaptic signaling is the method used by nerves to transmit their impulse or action potential across one nerve to another. The name is derived from the synapse. Synapses are the junction between two nerves. It contains a neurotransmitter that acts as a ligand, which then binds to the receptor present on the membrane of the second nerve. The common ligand that is used is acetylcholine, and the gated ion channel receptor mediates the signal transduction. The binding of a neurotransmitter opens the gated ion channel, which changes the electrical potential of the cell, and thus the signal travels from one nerve to another.
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Autocrine signaling is a type of signaling where the cell releases a chemical molecule, which acts as a ligand that binds to the receptor on the cell that produces it. This type of signaling is generally observed in the self-activatory molecules and as part of the immune response. The most important example of autocrine signaling is apoptosis, it can be defined as programmed cell death. In this case phosphatidylserine, a molecule present on the inner leaflet of the plasma membrane moves towards the extracellular side, acting as a ligand for apoptosis.
It also plays an important role in immune response cytokine production and regulation is mediated by the autocrine signaling pathway.
It is a long-distance signaling pathway, and a ligand molecule is transported over a long distance to which it binds to the receptor. The best example of this type of signaling is hormones, hormones from various glands are poured into the bloodstream and they travel along with it. When they reach the target cell, they bind to receptors generating the appropriate response.
Cell to Cell Contact Signaling
It occurs when two cells are connected through gap junctions or plasmodesmata in the case of plants, these junctions provide a channel through which ligand molecules can travel. Ligand in this case is known as intracellular mediators, which brings the response.
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