For many years we have studied glutamate receptors, with an emphasis on the N-methyl-D-aspartate (NMDA) receptor. Glutamate receptors play a major role in excitatory signaling in the brain and are involved in the induction of various forms of synaptic plasticity. Because these receptors can also trigger neuronal cell death, they are targets for neuroprotective drugs. Some of our work is centered around understanding the molecular basis of the complex modulatory effects of polyamines, protons, and of the novel antagonist ifenprodil. Another focus is the site and mechanism of action of open-channel blockers. Several model systems are used for these studies, which blend the concepts and questions of traditional receptor pharmacology with modern cellular and molecular techniques. Currently, our major focus involves studies of recombinant glutamate receptors expressed in oocytes. One approach involves site-directed mutagenesis and the construction of chimeric receptor subunits to define regions and individual amino acids in the receptor protein that are important for binding and/or function of particular ligands. A second, complimentary approach involves the use of novel polyamine derivatives to probe glutamate receptor channels. A related project is concerned with the channel pore properties of "orphan" delta receptors. In collaboration with Dr. Kazuei Igarashi in Japan, we are carrying out biochemical studies of portions of glutamate receptors expressed as soluble proteins.
Our work on GABAA receptors is carried out in collaboration with Dr. Sheryl Smith at Downstate. Those studies are concerned with the effects of alcohol and neurosteroids on recombinant GABAA receptors expressed in oocytes.
In collaboration with Drs. Nicholas Penington and Robert Wong at Downstate, we are using patch-clamp recording to study the properties of recombinant TRPC channels expressed in HEK-293 cells and activated by metabotropic glutamate receptors. Activation of TRPC channels may underlie the appearance of a novel cation conductance, discovered by Dr. Wong and colleagues, that is involved in some forms of epileptogenesis.
Figure 1. Modeling block of NMDA channels and residues at which mutations affect block or produce constitutively open channels.
Figure 2. Complex pharmacology of NMDA receptors.
Chao, J., Seiler, N., Renault, J., Kashiwagi, K., Masuko, T., Igarashi, K., and Williams, K. (1997). N1-Dansyl-spermine and N1-(n-octanesulfonyl)-spermine, novel glutamate receptor antagonists: block and permeation of N-methyl-D-aspartate receptors. Mol. Pharmacol. 51, 861-871.
Kashiwagi, K., Pahk, A. J., Masuko, T., Igarashi, K., and Williams, K. (1997). Block and modulation of N-methyl-D-aspartate receptors by polyamines and protons: role of amino acid residues in the transmembrane and pore-forming regions of NR1 and NR2 subunits. Mol. Pharmacol. 52, 701-713.
Williams, K., Pahk, A. J., Kashiwagi, K., Masuko, T., Nguyen, N.D., and Igarashi, K. (1998). The selectivity filter of the N-methyl-D-aspartate receptor: a tryptophan residue controls block and permeation of Mg2+. Mol. Pharmacol. 53, 933-941.
Masuko, T., Kashiwagi, K., Kuno, T., Nguyen, N. D., Pahk, A. J., Fukuchi, J., Igarashi, K., and Williams, K. (1999). A regulatory domain (R1-R2) in the amino terminus of the N-methyl-D-aspartate receptor: effects of spermine, protons, and ifenprodil, and structural similarity to bacterial leucine/isoleucine/valine binding protein. Mol. Pharmacol. 55, 957-969.
Kashiwagi, K., Masuko, T., Nguyen, C. D., Kuno, T., Tanaka, I., Igarashi, K, and Williams, K. (2002). Channel blockers acting at N-methyl-D-aspartate receptors: differential effects of mutations in the vestibule and ion channel pore. Mol. Pharmacol. 61, 533-545.
Sundström-Poromaa, I., Smith, D. H., Gong, Q. H., Sabado, T. N., Li, X., Light, A., Wiedmann, M., Williams, K., and Smith, S. S. (2002). Hormonally regulated α4β2ζ GABAA receptors are a target for alcohol. Nature Neurosci. 5, 721-722.
Masuko, T., Kusama-Eguchi, K., Sakata, K., Kusama, T., Chaki, S., Okuyama, S., Williams, K., Kashiwagi, K., and Igarashi, K. (2003). Polyamine transport, accumulation and release in brain. J. Neurochem. 84, 610-617.
Williams, K., Dattilo, M., Sabado, T. N., Kashiwagi, K., and Igarashi, K. (2003). Pharmacology of ζ2 glutamate receptors: Effects of pentamidine and protons. J. Pharmacol. Exp. Ther. 305, 740-748.
Kashiwagi, K., Tanaka, I., Tamura, M., Sugiyama, H., Okawara, T., Otsuka, M., Sabado, T. N., Williams, K., and Igarashi, K. (2004). Antheroquinone polyamines: novel channel blockers to study NMDA receptors. J. Pharmacol. Exp. Ther. 309, 884-893.
Thomas Sabado, Research Technician
Yanai Zhan, Ph.D. student
Michael Dattilo, M.D./Ph.D. student
Editorial board, Molecular Pharmacology. Ad hoc reviewer for various journals and funding agencies.