The Human Serotonin 1A Receptor Expressed in Neuronal Cells: Toward a Native Environment for Neuronal Receptors

Abstract

Accumulation of the branched-chain alpha-keto acids (BCKA), alpha-ketoisocaproic acid (KIC), alpha-keto-beta-methylvaleric acid (KMV), and alpha-ketoisovaleric acid (KIV) and their respective branched-chain alpha-amino acids (BCAA) in tissues and biological fluids is the biochemical hallmark of patients affected by the neurometabolic disorder known as maple syrup urine disease (MSUD). Considering that brain energy metabolism is possibly altered in MSUD, the objective of this study was to determine creatine kinase (CK) activity, a key enzyme of energy homeostasis, in C6 glioma cells exposed to BCKA. The cells were incubated with 1, 5, or 10 mM BCKA for 3 h and the CK activity measured afterwards. The results indicated that the BCKA significantly inhibited CK activity at all tested concentrations. Furthermore, the inhibition caused by the BCKA on CK activity was totally prevented by preincubation with the energetic substrate creatine and by coincubation with the N-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, indicating that deficit of energy and nitric oxide (NO) are involved in these effects. In contrast, other antioxidants such as glutathione (GSH) and trolox (soluble Vitamin E) were not able to prevent CK inhibition. In addition, we observed that the C6 cells changed their usual rounded morphology when exposed for 3 h to 10 mM BCKA and that creatine and L-NAME prevented these morphological alterations. Considering the importance of CK for brain metabolism homeostasis, it is conceivable that inhibition of this enzyme by increased levels of BCKA may contribute to the neurodegeneration of MSUD patients.

The function of G-protein coupled receptors and membrane cholesterol: specific or general interaction?

“…Nonetheless, cultured cells heterologously expressing GPCRs have made it possible to address important aspects related to membrane organization and function of GPCRs. The development of newer and more sensitive technologies that determine the interactions of GPCRs with membrane lipids and their influence on receptor function in a more nativelike membrane environment [88] would provide a more comprehensive understanding of GPCR function.…”

Membrane Organization and Function of the Serotonin1A Receptor

“…Subsequently, genes for the rat and mouse serotonin 1A receptors have been cloned, and their amino acid sequences deduced (Albert et al 1990;Charest et al 1993). These developments facilitated stable expression and characterization of the receptor in a number of neural and non-neural cell lines (Banerjee et al 1993;Newman-Tancredi et al 1997;Paila and Chattopadhyay 2006). Furthermore, it was the first serotonin receptor for which polyclonal antibodies were obtained (Fargin et al 1988;Pucadyil et al 2005a) allowing their visualization at the subcellular level in various regions of the brain.…”

Synthesis, physicochemical characterization and membrane interactions of a homologous series of N-acylserotonins: Bioactive, endogenous conjugates of serotonin with fatty acids

“…Serotonin, an endogenous molecule that acts as a neurotransmitter, is widely distributed in the central and peripheral nervous system, as well as other parts of the body [14]. Serotonin exerts its diverse actions by binding to specific cell surface receptors such as the serotonin 1A receptor, an extensively studied member of G-protein coupled receptor family, which plays a key role in serotonergic signaling [15,16]. Due to the high abundance of serotonin in the intestine, and central nervous system (CNS) [17][18][19][20], it may be speculated that N-acylserotonins would be formed in the gastrointestinal tissues and in the CNS.…”