IP Excretiony

A transporter-like protein inebriated, which responds to osmotic stimuli, is involved in potassium transport

C. S. Chiu, L. S. Ross & S. S. Gill

Dept. Cell Biol. & Neuroscience, Univ. California, Riverside, CA 92521, USA

The Na + /Cl - dependent neurotransmitter transporter superfamily consists of proteins involved in transport of neurotransmitters (GABA, serotonin, dopamine, norepinephrine, epinephrine, glycine, proline), osmolytes (taurine, betaine), and a metabolite (creatine). Recently we cloned a transporter-like protein inebriated, MasIne, from Manduca sexta. Phylogenetic analysis shows this protein is divergent from other neurotransmitter transporters, suggesting it probably has a distinct function from that of the other transporters. Using heterologous expression in Xenopus we show that oocytes expressing MasIne do not transport any of the commonly known ligands but respond to hyperosmotic stimulation, which causes the release of intracellular Ca 2+ . In Xenopus oocytes this release stimulates endogenous calcium-activated Cl - currents. This Ca 2+ release requires the N-terminus and occurs via the IP3 signaling pathway. Fusion of this N-terminus to the rat ?-aminobutyric acid transporter (rGAT1) also renders rGAT1 responsive to hyperosmotic stimulation. Immunohistochemical analyses show MasIne is distributed in tissues involved in potassium transport, including the goblet cells in the midgut, the Malpighian tubules, the hindgut and the central nervous system. We propose that stimulation of MasIne releases intracellular Ca 2+ in native tissues, activating Ca 2+ -dependent K + channels, leading to K + transport. This is the first report showing involvement of the IP3 signaling cascade in a member of the Na + /Cl - dependent neurotransmitter transporter. The ability of a transporter protein to activate intracellular signaling suggests these transporter proteins may have more diverse functions than previously believed. (Supported in part from a grant from the US National Institutes of Health)

Index terms: Manduca sexta; IP3, calcium-activated, channels

Copyright: The copyrights of this abstract belong to the author (see right-most box of title table). This document also appears in Session 13 – INSECT PHISIOLOGY, NEUROSCIENCES, IMMUNITY AND CELL BIOLOGY Symposium and Poster Session, ABSTRACT BOOK II – XXI-International Congress of Entomology, Brazil, August 20-26, 2000.