Cell communication is a process composed of intercellular and intracellular communication. Thus, information is first exchanged between cells via messenger substances. Within the cell, the signal is then transmitted and even amplified via receptors and secondary messengers.
What is cell communication?
Cell communication is a process composed of intercellular and intracellular communication. Cell communication is used to relay external stimuli by transmitting signals between cells and within cells. External signal transduction occurs via specific messengers such as hormones, neurotransmitter-mediated or ion-mediated electrical stimulus transduction, cell-bound surface molecules, or high molecular weight substances in the intercellular space. The signals enter the cell interior via receptors or so-called gap junctions and trigger a cascade of reactions there, depending on the transmission pathway. Thus, second messengers (secondary messenger substances) are formed in the cell, which transmit the signal to the target site and amplify it at the same time. Signal amplification occurs because an external signal results in the formation of a large number of second messengers. In contrast to intercellular communication, in intracellular communication the signals are processed in the cell and converted into a reaction. Here, the information is not transmitted from cell to cell, but is passed on by chemical messengers under amplification to the cellular target site. This entire process of intracellular communication is also known as signal transduction.
Function and task
In multicellular organisms, intracellular communication processes signals transmitted by extracellular messengers as well as by external stimuli (hearing, vision, smell). Signal transduction regulates important biological processes such as gene transcription, immune response, cell division, light perception, odor perception, or muscle contraction. The onset of intracellular communication is triggered by extracellular or intracellular stimuli. Extracellular triggers include hormones, growth factors, cytokines, neurotrophins or neurotransmitters. Furthermore, environmental influences such as light or sound waves are also extracellular stimuli. Intracellularly, calcium ions often trigger the signal transduction cascades. The extracellular signals are first taken up by receptors located in the cell or in the cell membrane. A distinction is made between cytosolic and membrane receptors. Cytosolic receptors are located within the cell in the cytoplasm. They represent targets for small molecules that can easily pass through the cell membrane. These include steroids, retinoids, carbon monoxide and nitric oxide. For example, steroid receptors, once activated, provide for the formation of second messengers responsible for transcription processes. The membrane-bound receptors are located in the cell membrane and have both extracellular and intracellular domains. During signal transduction, the signal molecules dock at the extracellular domain of the receptor and, by changing its conformation, ensure that the signal is transmitted to the intracellular domain. There, biochemical processes then take place that allow a cascade of second messengers to form. The membrane receptors are divided into three groups, the ion channels, the g-protein coupled receptors and the enzyme coupled receptors. Among the ion channels, there are again ligand-gated and voltage-gated ion channels. These are transmembrane proteins that are activated or deactivated depending on the signal, thereby changing the permeability to certain ions. A g-protein-coupled receptor, when activated, causes the G-protein to break down into two components. These two components are active and ensure the transmission of the signal by forming certain second messengers. Enzyme-coupled receptors are also membrane-bound receptors that release the enzymes bound to them upon signal transmission. Thus, there are six classes of enzyme-linked receptors. Depending on the receptor activated, the corresponding signals are transduced. For example, the receptor tyrosine kinase represents the receptor for the hormone insulin. Thus, the effect of insulin is mediated via this receptor. Some cells are connected via so-called gap junctions.Gap junctions are channels between neighboring cells and represent a form of intracellular communication. When a signal reaches a particular cell, gap junctions ensure its rapid propagation within neighboring cells.
Diseases and disorders
Disruptions in intracellular communication (signal transduction) are possible at many points in the signal transduction process and can have various health effects. Many diseases result from insufficient efficacy of certain receptors. If immune cells are affected, immunodeficiencies occur as a consequence. Autoimmune diseases and allergies are caused by the faulty processing of intracellular signal transduction processes. But diseases such as diabetes mellitus or arteriosclerosis are also often the result of ineffective receptors. In diabetes, for example, there may be sufficient insulin. However, due to missing or ineffective insulin receptors, insulin resistance exists in this case. As a result, even more insulin is produced. Eventually, the pancreas may become exhausted. Many mental illnesses can also be traced back to disturbances in intracellular cell communication, because in many cases signal transmission is not sufficiently ensured by insufficiently effective receptors for neurotransmitters. Neurotransmitters also play an important role in mental illness. For example, researchers are investigating which disorders in the complex processes of signal transmission can lead to diseases such as depression, mania, bipolar disorder or schizophrenia. Genetic causes can also lead to a disturbance in intracellular communication. One particular example of hereditary disorders relates to gap junctions. As mentioned earlier, gap junctions are channels between neighboring cells. They are formed by transmembrane proteins called connexin complexes. Several mutations of these protein complexes can lead to profound hearing loss or even deafness. Their cause lies in the defective function of the gap junctions and the resulting disruption in cell communication.
