Types of Hormone Receptors

In addition, the net charge of the hormone could also influence its binding ability. Thus, the observation of conformational patterns among thyroactive structures which correlate with function, activity and binding data provide useful information in describing specific types of hormone-receptor interactions. 

The unique or specific action of a hormone on its target tissue is a function of the interaction between the hormone and its receptor. As discussed above, there are several types of hormone-receptor interaction. The hormone-receptor complex provides the very high specificity of the action of the hormone, allowing the target tissue to accumulate the hormone from among all the molecules to which it is exposed. This is essential since hormones generally circulate in pico-molar or nanomolar concentrations (10 to 10 mol/L). 

On the postsynaptic side, there are specific receptors located in the membrane on to which the transmitter binds, in a similar way to the type of hormone-receptor interaction proposed in the previous chapter. (It is also possible that cAMP is involved in the postsynaptic response to some transmitters.) The transmitter-receptor results in a change in the postsynaptic membrane structure. If the receptor is an excitatory one, this may result in an influx of Ca++ ions large enough for the postsynaptic membrane to become depolarized. If a sufficient number of synapses transmit excitatory messages to the postsynaptic nerve at around the same time, the result will be a general depolarization, and the second nerve wil 14 fire or the muscle contract. 

Among vertebrate species, the neuro-endocrine-immime system is responsible for many complex, inter-related physiological processes including neuronal, homeostatic, reproductive and immune functions. There are four main types of hormone polypeptides, eicosanoids, steroids and thyroid hormones. Reflecting the inter-dependency of the neiiro-endocrine and immune systems, hormones, neuropeptides and other neiirotransmitters are known to be produced by some immune cells and play a role in the regulation of the immune system, while endocrine and nervous tissues express receptors for many substances produced by the immune system. The major focus of interest in endocrine disruption has... 

Vasopressin also plays an important role in short-term regulation of blood pressure through its action on vascular smooth muscle. This hormone is the most potent known endogenous vasoconstrictor. Two types of vasopressin receptors have been identified V, receptors mediate vasoconstriction... 

Burnstock, G. A basis for distinguishing two types of purinergic receptor. In L. Bolis and R. W. Straub (eds), Cell Membrane Receptors for Drugs and Hormones A Multidisciplinary Approach. New York Raven Press, pp. 107-118,1978. 

The family of heterotrimeric G proteins is involved in transmembrane signaling in the nervous system, with certain exceptions. The exceptions are instances of synaptic transmission mediated via receptors that contain intrinsic enzymatic activity, such as tyrosine kinase or guanylyl cyclase, or via receptors that form ion channels (see Ch. 10). Heterotrimeric G proteins were first identified, named and characterized by Alfred Gilman, Martin Rodbell and others close to 20 years ago. They consist of three distinct subunits, a, (3 and y. These proteins couple the activation of diverse types of plasmalemma receptor to a variety of intracellular processes. In fact, most types of neurotransmitter and peptide hormone receptor, as well as many cytokine and chemokine receptors, fall into a superfamily of structurally related molecules, termed G-protein-coupled receptors. These receptors are named for the role of G proteins in mediating the varied biological effects of the receptors (see Ch. 10). Consequently, numerous effector proteins are influenced by these heterotrimeric G proteins ion channels adenylyl cyclase phosphodiesterase (PDE) phosphoinositide-specific phospholipase C (PI-PLC), which catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) and phospholipase A2 (PLA2), which catalyzes the hydrolysis of membrane phospholipids to yield arachidonic acid. In addition, these G proteins have been implicated in... 

The locus of the encounter between hormone and receptor may be extracellular, cytosolic, or nuclear, depending on the hormone type. The intracellular consequences of hormone-receptor interaction are of at least six general types (1) a change in membrane potential results from the opening or closing of a hormone-gated... 

Most hormones affect their target cell by interacting with a specific receptor. Hormone receptors are located at three locations, shown in Figure 28-2. These primary locations are on the surface membrane of the cell, within the cytosol of the cell, or within the cell s nucleus.2 Receptors at each location tend to be specific for different types of hormones and also tend to affect cell function in a specific manner. Each type of receptor is briefly discussed below. 

Schaefer L, Malchow M, Schaefer RM et al. (1996) Effects of parathyroid hormone on renal tubular proteinases. Miner Electrolyte Metabol 22 182-186 Shimizu T, Hata S, Kuroda T et al. (1999) Different roles of two types of endothelin receptors in partial ablation-induced chronic renal failure in rats. Eur J Pharmacol 381 39-49 Stockelman MG, Lorenz JN, Smith FN et al. (1998) Chronic renal failure in a mouse model of human adenine phos-phoribosyltransferase deficiency. Am J Physiol 275 Renal Physiol 44 F154-F163... 

Hormone receptors can be classified into three types on the basis of their locations in the cell and the types of hormone they bind ... 

In Section 16.5, each type of hormone mechanism is briefly described. This is followed by a discussion of the insulin receptor, a critically important cellular component. 

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