Very similar findings have been made using mpkCCDc14 mouse kidney cells (Chassin et al., 2007) or MDCK cells (with a dissociation constant in the nanomolar range, too; Dorca-Arévalo et al., 2012). Taken together these observations suggest that ET binds to single receptor type, possibly expressed by both neural and renal cells (but see below). However, since ET can form pores (see §6.3) into artificial membrane bilayers (Nagahama et al., 2006; Petit et al., 2001) that are devoid of specific receptor for ET, ET binding to its receptor is not absolutely indispensable for pore formation. ET binding to isolated membranes Ku-0059436 nmr from rat brain (Nagahama and Sakurai, 1992) or to white matter
mice cerebellum slices (Dorca-Arévalo et al., 2008) is inhibited by treatment with pronase. On the contrary, ET binding to target cells click here is not or weakly affected by phospholipase C, glycosidases, or neuraminidase (Dorca-Arévalo et al., 2008; Nagahama and Sakurai, 1992). Therefore, ET receptor
on neural cells (including certain neurons and oligodendrocytes) is likely to be a protein or a glycoprotein. This corroborates prior deduction on the protein nature of ET receptor on renal cells (Petit et al., 1997). Differences in molecular weight of ET-binding proteins (i.e. receptor candidates) in renal and brain cells suggest that distinct proteins may be implicated into ET binding (reviewed by Popoff, 2011a). Hepatitis-A virus cellular receptor 1 (HAVCR1, also termed KIM-1 for Kidney injury molecule-1) has been shown contributing to ET binding (Ivie and McClain, 2012; Ivie et al., 2011). However no role is known for this protein in the nervous system as yet. Contribution of ganglioside
moiety to ET 17-DMAG (Alvespimycin) HCl binding onto the cell membrane is supported by early observation that treatment with neuraminidase decreases ET-binding on rat brain homogenates or synaptosomal membranes, leading to the proposal that ET-receptor might be a sialoglyprotein (Nagahama and Sakurai, 1992) or an O-glycoprotein (Dorca-Arévalo et al., 2008). Treatment by sialidase can modify the ganglioside content in membrane and has been shown modulating ET binding on MDCK cells (Shimamoto et al., 2005). Inhibition of sphingolipids and glycosphingolipids synthesis increases susceptibility of MDCK cells to ET, whilst inhibition of sphingomyelin decreases it. The presence of GM1 decreases the effects of ET, while GM3 does the contrary (Shimamoto et al., 2005). Above observations are compatible with ET binding to a double receptor comprised of a protein and ganglioside(s), as it has been described for clostridial neurotoxins (reviewed by Binz and Rummel, 2009). After binding to its receptor, ET but not proET oligomerizes (reviewed by Bokori-Brown et al., 2011; Popoff, 2011a) to form a large membrane complex of 155 kDa–200 kDa in rat synaptosomes (Miyata et al., 2002, 2001), mouse brain homogenates (Nagahama et al.