Some receptor places

Some receptor places, for example for Acetylcholinum and catecholamins, are characterised by means of labelled antagonists. Rather low affinity receptors to cholinergic or low concentration specific b-adrenergic places on cells-targets is framed by difficulties for the characteristic of these receptors by researches with application order cheap ultram of labelled agonists. The opinion on a cellular membrane as about a scene of action hormones was generated on the basis of observations Sutherland according to which interaction of catecholamins with a plasmatic membrane of erythrocytes of a pigeon leads to activation of adenylatecyclase [4]. After that it has been shown, that many hormones contact receptors of a plasmatic membrane and influence the activity localised in it, such, as adenylatecyclase or mechanisms of ionic transport ( 4-2). That fact testifies To superficial localisation of receptors hormones also, that short-term influence of a hormone causes long reaction of cells-targets which it is possible to charge to the bound hormone, and also ability of specific antiserums quickly to terminate hormones in vitro. It is known also, that enzymes or other agents influencing membranous fibers and lipids, modify or liquidate ability hormones to stimulate adenylatecyclase.
The most weighty proofs of localisation of receptors hormones on a plasmatic membrane have been received in researches and direct experiences on linkage of labelled biologically active hormones with preparations of membranes or intact cells. These approaches have allowed to find out precisely localisation and parametres of linkage of cellular receptor sites, and also their functional communication with cell-target reactions. Ability hormones to co-operate with cells-targets (or on the contrary) should depend on presence of specific binding sites on a plasmatic membrane (receptors) which take molecules carrying the information from an extracellular liquid. So, "awareness" of cells of a fascicular zone of a cortex of adrenals in the relation regulating influences is defined by concentration and a profile of secretion , arriving to epinephral glands. Extremely low concentration (nearby 10~10 M) in blood at excess of other fibers demand hormones, that receptors of cells-targets possessed as high specificity (allowing to learn a hormone), and high affinity to a hormone (allowing to bind it at low concentration). Well studied class of receptors for "traditional" hormones (such as peptides of a pituitary body and hormones of a gastroenteric tract) has replenished with similar sites for local and molecules (such as Acetylcholinum, catecholamins and Prostaglandinums), and later and for the group consisting approximately from 20 neuropeptids (as before known, and recently found out) which regulate, apparently, function of peripheric and central nervous system. This huge number hormones is characterised by a high charge and a relative hydrophylic nature, absence of appreciable linkage with fibers of plasma and ability to be bound to specific distinguishing sites on open area of receptor molecules. The cells-targets vpxl for you built in a plasmatic membrane. Consider, that other specialised area internal, with a membrane, parts of receptors hormones co-operates with an intramembranous part molecules or enzymes, such as adenylatecyclase, whose catalytic domain is accessible with internal, cytoplasmatic, surfaces of a cellular membrane. Though now it is known, that many hormones after linkage with superficial receptors nevertheless get into a cell, initial interaction with an external surface of a plasmatic membrane is a necessary condition of stimulation of reactions of cells-targets as intracellular introduction hormones does not cause characteristic reactions of such cells. Behind linkage of a hormone with a superficial receptor there comes activation of one or more membranous the systems, defining changes in mechanisms of transport and distribution of ions, and also activation of cytoplasmatic processes which regulate cell-target function. Many of these stages of activation include, apparently, membranous or cytoplasmatic fibers that leads to change of the enzymatic functions responsible for transport a metabolism of molecules, playing the important role in cellular activity. The main membranous enzyme regulated by hormones, adenylatecyclase, formation , necessary for processes , arising is at cell-target stimulation. To other membranous enzymes which activity is influenced by a hormone-receptor interaction, the enzymes participating in a circuit , the methyltransferases which are taking part in a methylation , and also , responsible for membranous concern. Last process is a source of formation of precursors (such, as arachidonic acid) of Prostaglandinums, , and other active metabolites. Hormonal influences on Na +, To +-dependent , the protein kinase bound to a membrane and a catechol-about-methyltransferase were observed also. Thus, at level of a plasmatic membrane hormones induce set of the processes participating in integrated reactions of cells-targets on activation of receptors homologous .

THE CHARACTERISTIC

THE CHARACTERISTIC OF RECEPTORS OF HORMONES Researches on the linkage, spent with the help radioactive atoms of hormones, have allowed to tap some prominent features inherent to receptors many of hormones. Universal line of receptors is their ability to distinguish and bind corresponding chemical transmitters buy cipro 500 mg or hormones in the presence of excess of molecules of other kinds. This property is easily shown in the presence of a labelled hormone as selective reaction of linkage with high affinity which leads to formation specific a complex. For the last years such interactions were observed in many tissues. In many researches presence of specific binding places in corresponding target tissues accepted for the proof of presence of hormonal receptors. Specific binding places are found out also in cells as which it is not accepted to consider as cells-targets, for example receptors of insulin and in lymphocytes, Prolactinum receptors in a liver and adrenals. If to consider, that correct representation about receptors assumes presence not only distinguishing, but also a component starting reaction under such definition receptors for which functional reaction while remains not found out, and also receptors which are allocated do not approach, or are located on nonreacting cellular components. Thus, the receptor is characterised by specific linkage and ability to transfer a signal even if distal elements of reaction are absent or . The fullest representation about a receptor a hormone includes double functional properties: superficial recognition and translation interactions in specific biological reaction. Irrespective of, whether secretion of peptides, a steroidogenesis, reduction or transport of ions, the mechanisms mediating hormonal effect is cellular reaction, usually include change of calcium streams and a metabolism of cyclic nucleotides.
On membranous fractions or intact cells of many target tissues observed dependence between linkage of a hormone and biochemical reactions. Correlation between a saturation of receptors and activity of adenylatecyclase is shown on preparations of membranes of many cells, for example cells of an adrenal in case of action , a liver in case of action of a glucagon, kidneys at addition of a vasopressin, erythrocytes of birds under the influence of catecholamins, seed canaliculuses in the presence of , and also spermaries and ovaries in the presence of and . In intact tissues and the isolated cells-targets hormone linkage also correlated with synthesis and liberation [6]. Correlation of linkage of a hormone with the subsequent cellular reactions observed concerning insulin and glucose oxidation in fatty cells or transport of amino acids order acomplia rimonabant in thymocytes, catecholamins and sodium transport in erythrocytes. and production of androgens spermaries, and also angiotensin II and production of Aldosteronum cells of a glomerular zone of an adrenal. Sometimes believe, that it is necessary to name hormonal receptors only those binding places of a tissue which can be identified with certain biochemical reaction. However specific linkage labelled under condition of observance of adequate demands to a technique of its definition all is the weighty indicating on presence of hormonal receptors. Such demands concern use of a labelled hormone with distinct biological activity (received with the help or ), an exact estimation of nonspecific linkage and an exception of linkage with blasting or others enzymatic , present at fabric fractions. The majority of receptors hormones shows high specificity in relation to biologically active hormones or their derivatives, the high affinity of linkage characterised by constants; Equilibriums of association of an order 109-1011 ~1, and saturability at rather low concentration of a hormone. Last properties correspond to low concentration of hormonal receptors in a target tissue which makes usually all a little thousand places on a cell. Linkage reaction always depends on temperature, differs high rate and in cell-free preparations is usually reversible. In intact cells the irreversible component of linkage of a hormone recently has been found out, and for Thrombinum and the factor of growth of a false skin () covalent joining to a receptor has been shown. Exact definition of constants of linkage and thermodynamic properties of receptors often is at a loss that in experiences on the linkage, spent in vitro at physiological temperatures, hormone and receptor degradation can take place. In the conditions inherent to experiments in vivo, also it is difficult to study kinetic and binding properties of receptors of hormones. On rate of association and hormone dissociation the big influence is rendered by temperature, and a circuit of molecules of a hormone in places at characteristic for an organism temperature and perfusion conditions is studied insufficiently. The albuminous nature of receptors of polypeptide hormones on a plasmatic membrane is proved by their splitting under the influence of various proteolytic enzymes and peptidases.