%0 Journal Article
%T Biochemical Evidence for a Putative Inositol 1,3,4,5-Tetrakisphosphate Receptor in the Olfactory System of Atlantic Salmon (Salmo salar)
%A Jiongdong Pang
%A Dennis E. Rhoads
%J Neuroscience Journal
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/460481
%X Olfactory receptor neurons in Atlantic salmon (Salmo salar) appear to use a phosphoinositide-directed phospholipase C (PLC) in odorant signal transduction. The consequences of odor-activated PLC depend on its product, inositol 1,4,5-trisphosphate (IP3). Therefore, a plasma membrane rich (PMR) fraction, previously characterized from salmon olfactory rosettes, was used to study binding sites for IP3 and its phosphorylation product, inositol 1,3,4,5-tetrakisphosphate (IP4). Binding sites for IP3 were present at the lower limit for detection in the PMR fraction but were abundant in a microsomal fraction. Binding sites for IP4 were abundant in the PMR fraction and thus colocalized in the same subcellular fraction with odorant receptors for amino acids and bile acids. Binding of IP4 was saturable and high affinity ( £¿=£¿83£¿nM). The rank order for potency of inhibition of IP4 by other inositol polyphosphates (InsPx) followed the phosphorylation number with InsP6 > InsP5 > other InsP4 isomers > InsP3 isomers > InsP2 isomers, with the latter showing no activity. The consequences of PLC activity in this system may be dictated in part by a putative receptor for IP4. 1. Introduction Adenylyl cyclase and cAMP appear to dominate odor signal transduction in mammals (for reviews, see [1¨C3]). Phosphoinositides may play a divergent role in olfaction, mediating inhibitory signaling through phosphoinositide-3-kinase [4] or excitatory signaling through phospholipase C [1, 5]. For fish, components of a phospholipase C-based olfactory signal transduction system have been characterized in catfish [6¨C13] and are seen in carp [14, 15], zebrafish [16], and Atlantic salmon [17, 18]. As potent olfactory stimuli for Atlantic salmon, amino acids and bile acids interact with distinct subclasses of olfactory receptors to begin the process of olfactory reception [18, 19]. The amino acid and bile acid receptors appear to be coupled through G proteins to the activation of phospholipase C (PLC) and the breakdown of phosphatidylinositol 4,5-bisphosphate (PIP2) to generate diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3) [17, 18]. Early biochemical data characterizing these as G protein-coupled receptors is now supported by molecular studies characterizing olfactory receptor gene sequences from Atlantic salmon [20¨C23]. Underscoring the importance of these receptors in salmon physiology, odorant receptor expression has been shown to change during the parr-smolt transformation, a period characterized by increased olfactory sensitivity and olfactory-based learning [24]. The
%U http://www.hindawi.com/journals/neuroscience/2013/460481/