Effector systems

Two AR subtypes, Ax and A3, couple through G to inhibit adenylate cyclase, while the other two subtypes, A2a and A2B, stimulate adenylate cyclase through Gs or G0if (for A2a). The A2BAR is also coupled to the activation of PLC through Gq. Furthermore, each of these receptors may couple through the (3,y subunits of the G proteins to other effector systems, including ion channels and phospholipases. Levels of intracellular... 

Ca may activate phospholipase A2 and cause production of lyso-lipids and fatty acids. In addition, ionic fluxes across the membrane occur, leading to pH changes and membrane depolarization. It is not clear how these other responses are initiated, but there may be direct G-protein links to effector systems such as phospholipase A2 or ionic channels. 

Conn, P.J., and Sanders-Bush, E. Central serotonin receptors Effector systems, physiological roles and regulation. Psychopharmacology 92 267-277, 1987. 

GTP Binding Proteins Act as Transducers between Receptors and Effector Systems... 

The large number of RGS proteins have varying degrees of selectivity for different a subunits and varying effects on different effector systems (see Vries et al., 2000). These properties are usually... 

The cloned opiate receptors expressed in homogeneous cell lines associate with guanine nucleotide binding (G) proteins which couple the receptors to cellular effector systems. G proteins consist of hetero-trimeric complexes of a, fj and y subunits [66]. Multiple subtypes of each subunit have been identified and cloned. In particular, three subtypes of Gi have been cloned that are approximately 90% identical in amino acid sequence. Furthermore, two splice forms of G0 have been identified. 

Mutagenesis studies have established that the C-terminal region of the // and S receptors is not essential for the receptors to couple to adenylyl cyclase [131, 132]. The remaining intracellular domains of the opiate receptors have almost identical amino acid sequences. As a consequence, it is likely that the intracellular loops are the main regions of the opiate receptor involved in G protein coupling and effector system regulation. 

Tallent M, Dichter M. Reisine T. Coupling of the cloned kappa and mu opioid receptors to cellular effector systems is differentially regulated. Neuroscience 1998 85 873-885. 

Carrero I, Femandez-Moreno MD, Perez-Albarsanz MA, et al. 1989. Lindane effect upon the vasoactive intestinal peptide receptor-effector system in rat enterocytes. Biochem Biophys Res Comm 159(3) 1391-1396. 

Mechanisms of Complement Activation. Complement is a major mediator of the inflammatory response. Complement recruits and enlists the participation of humoral and cellular effector systems, induces histamine release from mast cells and directs migration of leukocytes (chemotaxis), in addition to producing phagocytosis and the release of lysosomal constituents from phagocytes. 

The action of a hormone is defined as the primary effect on a cell, usually the binding of the hormone to a specific receptor and the resultant interaction between the hormone-receptor complex and an effector system within the cell. The effect of a hormone is an experimental observation that is made either in vitro or in vivo it can be molecular, biochemical or physiological but, when a sufficient number of effects are established, a relationship between the action and effects can be drawn. This can best be described as a pyramid (Figure 12.2). The. function of a hormone is an... 

Second, the complex stimulates an effector system which... 

For a cell surface receptor, the binding of the hormone must change the activity of an effector system that results in a change in concentration of an intracellular messenger. This is achieved by location of the effector system on the cytosolic side of the membrane, although the receptor and effector system may be combined in one complex. 

The receptors can either be located on the cell surface or within the cell. Not surprisingly, the mechanisms of the effector systems are, in principle, quite distinct for the two... 

Despite the existence of a large number of hormones, only four effector systems for linking hormone binding to an intracellular effect have been described ... 

The effector systems result in changes in messenger systems that then cause the effects of the hormone. Not surprisingly, the effects of the hormone depend on which hormone is being considered. To illustrate this four hormones - insulin, cortisol, adrenaline and glucagon - are discussed. 

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