Recent advances in amino acid transporters and excitatory amino acid receptors.

Complementary DNAs that encode proteins capable of biochemically defined system A-, N-, asc-, and T-like activities have been cloned. Functional expression and localization analyses of these proteins have revealed significant information about how transport is energized, what substrates are recognized, and where transporter messenger RNA or proteins are expressed. Still lacking, however, is definitive knowledge about transporter localization and how expression and function are coordinated with that of other transport proteins, enzymes, and receptors to support tissue physiology. Although the molecular identity of the physiologically relevant glutamate receptors has been known for nearly 10 years, work has progressed in the areas of molecular regulation, the localization of receptors to identified populations of neurons and glia, and the rate of turnover at the cell membrane. Collectively, these accomplishments enable the putative relationship between abnormal transporter or receptor functions to be correlated with the etiology of several diseases.