The TRPC Family of Ion Channels: Relation to the TRP Superfamily and Role in Receptor- and Store-Operated Calcium Entry

Excerpt

The Drosophila trp mutation is responsible for the phenotype called transient receptor potential, an alteration of the fly’s electrorentinogram in which its sustained phase is missing [1,2]. The responsible gene was cloned in 1989 [3]. Its amino acid sequence predicted a protein with eight hydrophobic segments that could potentially form transmembrane segments. Purification and cloning of a calmodulin-binding protein from Drosophila heads showed it to be a homologue of trp. It received the name trp-like or trpl [4]. Its discoverers highlighted the existence of limited sequence similarities between trp/trpl and voltage-sensitive Na⁺ and Ca²⁺ channels. Expression of trpl in silkworm cells of Spodoptera frugiperda (Sf9 cells) did indeed lead to appearance of cation channels [5]. In keeping with both a role for trp and trpl in insect phototransduction, and the fact that insect phototransduction is biochemically akin to mammalian signal transduction based on the Gq-PLC pathway instead of a transducin-phosphodiesterase (Gt-PDE) pathway [6,7], the trpl channels expressed in Sf9 cells could be activated by a Gq-coupled GPCR [8].