Receptor diffusivity

Figure 10. Equilibria between ligand and receptor in the homogeneous phase and at the heterogeneous phase. Non-blocked receptors diffuse by a transport-limited process to the surface and can form a second equilibrium. From this assay type, kinetic as well as thermodynamic constants can be determined.

ENCOUNTER-CONTROLLED RATE DIFFUSION-LIMITED REACTION CHEMICAL KINETICS DIFFUSION OF LIGAND TO RECEPTOR DIFFUSION OF MOLECULES INTO A PORE... 

Calcium ions are usually released in distinct pulses or "quanta." The kinetic characteristics of the system of receptors, diffusing InsP3, calcium buffers, and calcium pumps in the cell membrane, and the membrane potential may account for this behavior.174 301-306 Since... 

Serotonin Usually inhibitory helps control mood, influences sleep, and inhibits pain pathways in the spinal cord. Secreted by subcortical structures into hypothalamus, brain, and spinal cord. There are many subtypes of serotonin receptors. Diffuse and widespread symptoms depression, headache, diarrhea, constipation, sexual dysfunction, and other medical symptoms. The selective serotonin reuptake inhibitors (SSRIs), the most commonly used antidepressants, work specifically on this neurotransmitter system. 

Figure 1 General concept representation of synaptic transmission. Vesicles that contain neurotransmitter molecules dock to the cell membranes and release their contents into the synapse by exocytosis. Neurotransmitters can diffuse across the synapse and bind to postsynaptic receptors or can diffuse out of the synapse. This extrasynaptic neurotransmitter can bind to presynaptic receptors, diffuse away and activate receptors on distal neurons, or be cleared from the extracellular space by transporters.

As has been shown for FPR and other receptors diffusion of a receptor protein may be restricted by interaction with the membrane skeleton [5,50]. On the other hand, interaction of G proteins with cytoskeletal elements has also been demonstrated providing for a means to also control G protein distribution in the plasma membrane (for review see [57]). An intriguing idea explaining distinct membrane distribution of G proteins has been put forward by Rodbell and coworkers who observed polydisperse forms of G proteins caused by polymerization of G subunits in analogy to tubulin [58,59]. Formation of these large molecular complexes would result in restricted mobility of the G proteins and could serve as an explanation for membrane domains in neutrophils that are enriched in G proteins (see above). 

Most cholesterol Is transported In Ihe blood bound to protein in Ihe form of particles known as low-density lipoproteins, or LDL (Figure 13-29t. When a cell needs cholesterol for membrane synthesis, it makes transmembrane receptor proteins for LDL and inserts them Into Its plasma membrane. Once In the plasma membrane, the LDL receptors diffuse until they associate with clathrin-coated pits that are In the process of forming (Figure 13-30AL Since coated pits constantly pinch off to form coated vesicles, any LDL particles bound to LDL receptors in the coated pits are rapidly Internalized In coated vesicles. After shedding their clathrin coats, these vesicles deliver their contents to early endosomes. which are located near the cell... 

This lateral mobility within the membrane is important because it participates in the regulation of receptor binding to ligands. Receptor diffusivity determines the rate at which receptors can find each other, thereby determining the transport-limited rate of binding. Under purely diffusive mechanisms, the rate of receptor collision, k+ can be estimated according to the equation ... 

Point attachment [Hammer and Lauffenberger, 1987] Bonds are equally stressed in the contact area (flat) Binding and dissociation occur according to characteristic rate constants Receptors diffuse and convert into the binding area of contact Adhesion occurrence depends on values of dimensionless quantities that characterize the interaction between the cell and the surface... 

Compounds 44 and 45 were found to be insoluble in many common organic solvents however, compound 44 dissolves in DCM and 1,2-dichloroethane on the addition of tetrabutylanunonium chloride or tetrabutylammonium acetate—an early indication of the anion-binding capacity of this receptor. Diffusion of ether into a DCM solution of 44 in the presence of tetrabutylanunonium chloride yielded crystals of the chloride complex of 44 suitable for X-ray diffraction. The crystal structure revealed that two distinct complexes were present in the solid state (Figure 32). In both cases, the strongest hydrogen bonds to the chloride anion are from the carbazole NH (NH Cl 2.22 and 2.33 A). In the first complex, the chloride anion is asymmetrically positioned within the cavity. 

Choquet D, Triller A (2003) The role of receptor diffusion in the organization of the post-synaptic membrane. Nat Rev Neurosci 4 251-265... 

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