Second messengers interactions

Rafaeli A. and Soroker V. (1994) Second messenger interactions in response to PBAN stimulation of pheromone gland cultures. In Insect Neurochemistry and Neurophysiology, 1993, eds A. Borkovec and M. J. Loeb, pp. 223-226. CRC Press, Boca Raton, FL. 

These second messengers interact with yet another type of protein, the ion channels. They open the gates on the ion channels and allow positively charged ions to flow into the cell, therefore creating an electrical potential between the cell and its environment. This is relieved when the synapse at the other end of the cell, in the olfactory bulb, fires across to the next nerve cell in line and the transduction process is set in motion. The second messengers also set in train a process which deactivates the receptor by phosphorylation, and a dephosphorylation is necessary to make it active again. 

Oxytocin and Vasopressin Receptors. The actions of oxytocin and vasopressin are mediated through their interactions with receptors. Different receptor types as well as different second messenger responses help explain their diverse activities in spite of the hormones stmctural similarities. Thus oxytocin has at least one separate receptor and vasopressin has been shown to have two principal receptor types, and V2. Subclasses of these receptors have been demonstrated, and species differences further compHcate experimental analysis. It is apparent that both oxytocin and receptors function through the GP/1 phosphoHpase C complex (75), while the V2 receptors activate cycHc AMP (76). 

At a cellular level, the activation of mAChRs leads to a wide spectrum of biochemical and electrophysiological responses [1, 5]. The precise pattern of responses that can be observed does not only depend on the nature of the activated G proteins (receptor subtypes) but also on which specific components of different signaling cascades (e.g. effector enzymes or ion channels) are actually expressed in the studied cell type or tissue. The observed effects can be caused by direct interactions of the activated G protein(s) with effector enzymes or ion channels or may be mediated by second messengers (Ca2+, DP3, etc.) generated upon mAChR stimulation. 

The possible combinations generated by these mechanisms could be sufficient to account for ligand-specific and cell-specific biological responses, notwithstanding the limited number of second messengers that are available for the transcription of the primary response genes (Herschman, 1989). It is apparent that much remains to be done to understand the complexity of the cytoskeleton and its interactions within cells and across cell membranes. 

Berridge M. J. Inositol triphosphate and diacy(glycerol TWo interacting second messengers. Annu Rev Biochem 1987 56, 159-93. 

G-proteins are easy. The GTP-bound form can interact successively with several molecules of its target before the GTP is hydrolyzed and the G-protein is inactivated. The synthesis of cyclic nucleotide second messengers by the cyclase is also an obvious amplification step. 

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