Research in the Kavanaugh laboratory focuses on transporters and ion channels, membrane proteins involved in solute uptake and signaling in neurons and other cells. Kavanaugh and his associates integrate electrophysiological and molecular biological approaches in their work. Cloned transporters and channels are expressed in Xenopus oocytes or mammalian cells and studied using techniques including voltage-clamp recording, radiotracer flux measurement, and site-directed mutagenesis. Other studies are focused on the behavior of these molecules in native retinal neurons.

Elucidating the biophysical properties of ion channels and transporters is necessary for understanding the physiological roles of these molecules. In the brain, transporters mediate the reuptake of neurotransmitter following its release from the presynaptic cell. Kavanaugh and coworkers are particularly interested in the structural and functional properties of transporters for glutamate, the major central nervous system excitatory neurotransmitter. They are probing the molecular mechanisms involved in translocating glutamate across the cell membrane by examining flux of ions through the transporters as well as by analyzing the effects of mutations on this flux.

Glutamate transport is thermodynamically coupled to the cotransport of three sodium ions and one proton, and the countertransport of one potassium ion. However, a chloride channel is also associated with glutamate transporters and the channel open-probability increases when glutamate is present. The physiological role of this channel is unclear. Kavanaugh's lab is exploring its properties in terminals of retinal photoreceptors, where it may significantly influence the presynaptic membrane conductance. Another active area of research in the lab involves relating the chloride channel kinetics to glutamate transport kinetics. Understanding this relationship will allow the channel to be used to monitor the microscopic states of the transporter, providing a powerful tool for developing and testing kinetic models.

Other ongoing research involves studies of the tertiary and quaternary structures of glutamate transporters. Identification of residues involved in key functions such as ion selectivity and glutamate recognition are beginning to allow construction of more detailed models for the fundamental molecular processes involved in transporter gating and ion co- and countertransport. The oligomeric structure of the transporters is also being studied by coexpressing different proportions of wild-type transporter subunits together with mutant subunits with altered functional properties. Analysis of the resulting transport properties indicates that multiple subunits interact to form a functional complex. Functional modeling together with complementary biochemical studies are being used to define the subunit stoichiometry further.

Otis T.S., and Kavanaugh M.P. (2000) Isolation of current components and partial reaction cycles in the glial glutamate transporter EAAT2. J. Neurosci. 20:2749-57.

Otis T.S., and Kavanaugh M.P. (1999) Glutamate transporters and their contributions to excitatory synaptic transmission. Handbook of Exp. Pharmacol. 141:419-440.

Tzingounis A.V., Lin C.L., Rothstein J.D., and Kavanaugh M.P. (1998) Arachidonic acid activates a proton current in the rat glutamate transporter EAAT4. J. Biol. Chem. 273: 17315-17357.

Zarbiv R., Grunewald M., Kavanaugh M.P., and Kanner B.I. (1998) Cysteine scanning of the surroundings of an alkali-ion binding site of the glutamate transporter GLT-1 reveals a conformationally sensitive residue. J. Biol. Chem. 273:14231-14237.

Wadiche J.I., and Kavanaugh M.P. (1998) Macroscopic and microscopic properties of a cloned glutamate transporter/chloride channel. J. Neurosci. 18:7650-7661.