CONTINUOUS MONITORING OF L-GLUTAMATE RELEASED FROM CULTURED NERVE-CELLS BY AN ONLINE SENSOR COUPLED WITH MICRO-CAPILLARY SAMPLING

A small volume L-glutamate online sensor was developed in order to mon itor changes in the local concentration of L-glutamate released from c ultured nerve cells. Syringe pump in the suction mode is used to sampl e extracellular fluid continuously from a glass micro-capillary and th e concentration of L-glutamate can be determined by using a glassy car bon (GC) electrode modified with an Os-polyvinylpyridine mediator bott om film containing horseradish peroxidase and a bovine serum albumin t op layer containing L-glutamate oxidase. The overall efficiency of L-g lutamate detection with a sensor is 71% under optimum conditions due t o an efficient enzymatic reaction at the modified electrode in the thi n layer radial flow cell. As a result, we achieved a detection limit o f 7-15 nM and a linear range of 50 nM to 10 mu M. In an in vitro exper iment, the extracellular fluid near a particular nerve cell can be sam pled with this micro-piper and continuously introduced into the modifi ed GC electrode in the radial flow cell via suction provided by a syri nge pump. The nerve cells are stimulated by KCl in a glass capillary a nd the L-glutamate concentration change can be monitored by changing t he distance between the sampling pipet and the nerve cells. (C) 1997 E lsevier Science Limited.