Plasma-membrane-located signals

Biochemically, most quaternary ammonium compounds function as receptor-specific mediators. Because of their hydrophilic nature, small molecule quaternaries caimot penetrate the alkyl region of bdayer membranes and must activate receptors located at the cell surface. Quaternary ammonium compounds also function biochemically as messengers, which are generated at the inner surface of a plasma membrane or in a cytoplasm in response to a signal. They may also be transferred through the membrane by an active transport system. 

GPCR function has been shown to be regulated by several different mechanisms. The number of receptors on the plasma membrane may be regulated by transcription, mRNA stability, biosynthetic processing, and protein stability. In addition, the function of receptors in the plasma membrane can be influenced by regulatory phosphorylation and by association with other proteins that determine the subcellular location of receptors relative to other signaling molecules. 

G -protein-coupled receptors are often located on the presynaptic plasma membrane where they inhibit neurotransmitter release by reducing the opening of Ca2+ channels like inactivation and breakdown of the neurotransmitter by enzymes, this contributes to the neuron s ability to produce a sharply timed signal. An a2 receptor located on the presynaptic membrane of a noradrenaline-containing neuron is called an autoreceptor but, if located on any other type of presynaptic neuronal membrane (e.g., a 5-HT neuron), then it is referred to as a heteroreceptor (Langer, 1997). Autoreceptors are also located on the soma (cell body) and dendrites of the neuron for example, somatodendritic 5-HTia receptors reduce the electrical activity of 5-HT neurons. 

Ca2+ is the main intracellular signalling molecule in smooth muscle. Fluctuation in local cytoplasmic [Ca2+] near Ca2+-sensitive effector molecules allows for specific regulation of multiple functions. These temporal fluctuations and spatial variations of cytoplasmic [Ca2+] are dependent on the interactions of ion transport proteins located in the plasma membrane (PM) and membranes of the sacoplasmic reticulum (SR), nuclear envelope and mitochondria. These... 

To receive and pass on chemical or physical signals, cells are equipped with receptor proteins. Many of these are integral membrane proteins in the plasma membrane, where they receive signals from their surroundings. Other receptor proteins are located in intercellular membranes. The receptors for lipophilic hormones are among the few that function in a soluble form. They regulate gene transcription in the nucleus (see p. 378). 

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