Ionotropic state

The chemical messenger is unable to cross the plasma membrane because of low lipid solubility. The messenger binds to specific plasma membrane receptors (integral membrane proteins). In the ligand-bound state the receptors activate either (1) an intrinsic ion channel (ionotropic receptors) or (2) a defined sequence of enzymes (metabotropic receptors). Table 6.5 shows examples of plasma membrane receptors. 

There are two sub-types of glutamate receptors in glutamatergic structures in brain ionotropic and metabotropic ones, which differ in both localization (the former — predominantly on the postsynaptic membrane and the latter — on both post- and presynaptic membranes) and their functional role. Activation of ionotropic receptors provides electric activity of neurons (generation of action potential) whereas that of metabotropic receptors modifies metabolism of the neuronal cell and, in particular, conformational state and properties of ionotropic receptors this modifying effect is performed by second messengers which formation involves activation of subsequent G-proteins. 

Membrane lipids can exist in a number of intermediate states or mesophases more ordered than the liquid but less so than the crystalline solid [102, 131, 136]. Such materials are called liquid crystals and their multiple intermediate phase character is termed mesomorphism. There are at least four types of mesomorphic behavior lyotropic, thermotropic, barotropic and ionotropic. These refer to the expression of the disparate liquid crystal phases by manipulating solvent (lyotrope) content, temperature, pressure, and salt concentration, respectively. Most membrane lipids exhibit the four types of mesomorphism. 

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