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Synapses
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Ca2+ influx is influenced by the inherent properties of Ca2+ channels, and by the extracellular Ca2+ concentration – the larger this concentration the larger the influx, and conversely. Ca2+ influx is also influenced by the number of metabotropic receptors in the presynaptic terminal. Activation of these receptors affects, through second messengers, Ca2+ channels and both voltage-dependent and voltage-independent K+ channels in the presynaptic terminal. Inactivation of some K+ channels causes broadening of the AP, which increases Ca2+ influx, whereas gradual activation of a Ca2+-dependent K+ current reduces the amplitude of the AP, or its duration, or causes its failure altogether, which reduces Ca2+ influx. Some of these metabotropic receptors are autoreceptors, that is, they are receptors of the presynaptic membrane that are activated by neurotransmitters released from the same presynaptic terminal. Examples of such neurotransmitters are GABA and ATP. The activation of autoreceptors is a negative feedback mechanism that reduces Ca2+ influx and hence the release of neurotransmitters. The depression of transmission through autoreceptors is termed homosynaptic inhibition. The presynaptic metabotropic receptors could also be activated by neurotransmitters released into the extracellular space by other neurons in which case the inhibition is termed heterosynaptic inhibition.
Association between COMT Val158Met polymorphism and competition results of competitive swimmers
Published in Journal of Sports Sciences, 2018
Daisuke Abe, Hirokazu Doi, Taishi Asai, Mayuko Kimura, Tadashi Wada, Yuusuke Takahashi, Takaaki Matsumoto, Kazuyuki Shinohara
Finally, dopamine D3 receptor is an autoreceptor that inhibits the release of dopamine from dopaminergic neurons, which are mainly expressed in the nucleus accumbens (Bouthenet et al., 1991; Diaz et al., 2000; Savitz et al., 2013). An SNP in DRD3 resulting in substitution of the amino acid encoded by codon 9 from serine to glycine (DRD3 Ser9Gly) has been associated with depression (Schosser et al., 2011), as well as with motivation and emotional response (Savitz et al., 2013).