Biochemical Evidence for a Putative Inositol 1,3,4,5-Tetrakisphosphate Receptor in the Olfactory System of Atlantic Salmon (Salmo salar).

Jiongdong Pang,Dennis E Rhoads

doi:10.1155/2013/460481

Abstract

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 (K d = 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.

Highlights

Adenylyl cyclase and cAMP appear to dominate odor signal transduction in mammals
The goal of the present study was to characterize further the phospholipase C (PLC)-based olfactory signal transduction system of Atlantic salmon, beginning with the hypothesis that IP3 binding sites would colocalize with odor receptor binding sites in a plasma membrane rich fraction (PMR) that we characterized previously [17,18,19,20, 35]
At a radioligand concentration of 7 nM, no specific binding of IP3 was detectable with the olfactory PMR fraction

Summary

Introduction

Adenylyl cyclase and cAMP appear to dominate odor signal transduction in mammals (for reviews, see [1,2,3]). 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 4,5bisphosphate (PIP2) to generate diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3) [17, 18]. Biochemical data characterizing these as G protein-coupled receptors is supported by molecular studies characterizing olfactory receptor gene sequences from Atlantic salmon [20,21,22,23]

Objectives

Methods

Results

Conclusion