Distribution and lateral mobility of GABA/benzodiazepine receptors on nerve cells

The distribution and mobility of GABA/benzodiazepine receptors has been examined on living nerve cells by fluorescence digital imaging and fluorescence photobleach recovery with 2 novel fluorescent derivatives of the benzodiazepines Ro7-1986 and 1012S. These fluorescent derivatives retain their high affinity for the GABA/benzodiazepine receptor complex with Ks of 79 and 85 nM, respectively. Digital fluorescence imaging of GABA/benzodiazepine receptors on rat spinal cord neurons maintained in culture reveal that, even in the absence of observable synaptic contact, GABA/benzodiazepine receptors are localized on the cell body in clusters of very high density. Receptor density on processes is lower than on cell bodies, although occasional areas of intense fluorescence were observed. Fluorescence photobleach recovery measurements show that 70% of the GABA/benzodiazepine receptors on the cell body and greater than 85% on the processes of rat spinal cord neurons are immobile. In comparison, voltage-gated sodium channels are diffusely distributed and very mobile on the cell body (D = 10(-9) cm2/sec). The results suggest that even in the absence of nerve-nerve cell contact, there are specific mechanisms that segregate GABA/benzodiazepine receptors to the neuronal cell body and control their lateral mobility.