This section investigates the functional properties of neurotransmitter receptors in the vertebrate CNS utilizing electrophysiological and molecular biological techniques. Receptor selective agonists and antagonists are applied by rapid perfusion to cells and membrane patches under voltage clamp. Preparations in use include recombinant glutamate receptors expressed in transfected mammalian cells and Xenopus oocytes, and native glutamate receptors generated in primary cultures of selected CNS cells. Kinetic analysis of the molecular basis of AMPA receptor allosteric regulation is being investigated by generation of mutants in an extracellular domain controlling sensitivity to potentiation by cyclothiazide and aniracetam. In glial progenitor cells regulation of expression of native AMPA receptors by the growth factors PDGF and bFGF was analysed by electrophysiological techniques. Increased rectification after treatment with PDGF and bFGF revealed selective expression of polyamine sensitive subunits. The mechanism of polyamine induced rectification was characterized using GluR6(Q) homomeric receptors. Spermine and philanthotoxin (PhTX) block from both the cytoplasmic and external faces of the channel; external spermine block is very weak, and for PhTX the rate of recovery from block increases with hyperpolarization. An Eyring rate theory model with an asymmetrical external barrier higher for PhTX than for spermine adequately reproduced these features.
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