Protein kinases and light: unlikely partners in a receptor localization puzzle

Abstract

Brief flashes of light directed at neuronal cell bodies and proximal dendrites of neurons in culture can enhance whole-cell electrophysiological responses mediated by NMDA and GABA A receptors. In experiments aimed at identifying the molecular moieties responsible for mediating this phenomenon, we observed that broad-spectrum protein kinase inhibitors substantially amplified the actions of light. Kinase inhibitors, however, were surprisingly ineffective in altering light-induced potentiation of recombinant NMDA receptors expressed in Chinese hamster ovary (CHO) cells. Furthermore, receptors assembled from truncated NMDA receptor subunits, previously shown to be relatively insensitive to modulation via phosphorylation, remained light sensitive. Phosphatase inhibitors had no effects of lightinduced NMDA receptor potentiation in neurons, and nucleated patches excised from neuronal somata behaved similarly to CHO cells. Taken together, these data suggests that the effects of kinase inhibitors were unrelated to the molecular mechanism of light-induced potentiation. We propose a model whereby kinase inhibition promotes an enrichment of NMDA receptors in the neuronal cell body vs. the distal dendrites. Under these conditions, NMDA receptor redistribution elicited by kinase inhibitors would increase the number of receptors exposed to light and, as a consequence, the whole cell response. These observations support a critical role for protein kinases in the rapid redistribution of neurotransmitter receptors, with profound physiological significance. D

Reversible modulation of GABAA receptor‐mediated currents by light is dependent on the redox state of the receptor

“…As we have proposed before, modulation of ion channel function by both redox agents and light seem to be structurally linked within the receptor (Leszkiewicz & Aizenman, 2002). Specifically, we have shown that both GABA and NMDA receptor mediated responses are enhanced following exposure to light stimuli, and that reducing agents occlude the effects of light on these channels (Fig.…”

“…GABA A receptors have been shown to be redox sensitive (Pan et al ., 1995; Amato et al ., 1999; Pan et al ., 2000), and we have reported that an intact and oxidized functional redox site is necessary for the light induced potentiation of NMDA induced currents (Leszkiewicz & Aizenman, 2002). Therefore, we evaluated whether the effects of light would also be altered by the oxidation or reduction of recombinant α 1 β 2 GABA A receptors transfected in CHO cells.…”

“…Therefore, we evaluated whether the effects of light would also be altered by the oxidation or reduction of recombinant α 1 β 2 GABA A receptors transfected in CHO cells. We chose to use CHO cells for these experiments, as the light stimulus we utilize does not illuminate the entire population of receptors in our cultured neurons (due to their large and elaborate dendritic processes; Leszkiewicz et al ., 2002). Trials consisted of first testing the light sensitivity of receptors that had been previously oxidized by exposure to 500 n m DTNB for 2 min (–DTT; Fig.…”

“…Specifically, we have shown that both GABA and NMDA receptor mediated responses are enhanced following exposure to light stimuli, and that reducing agents occlude the effects of light on these channels (Fig. 4D; Leszkiewicz and Aizenman, 2002). Mutation of two cysteines on the NR1 subunit, responsible for redox modulation of the majority of NMDA receptor configurations (Sullivan et al ., 1994; Brimecombe et al ., 1999), nearly abolishes the effects of light on this channel (Leszkiewicz & Aizenman, 2002).…”

“…4D; Leszkiewicz and Aizenman, 2002). Mutation of two cysteines on the NR1 subunit, responsible for redox modulation of the majority of NMDA receptor configurations (Sullivan et al ., 1994; Brimecombe et al ., 1999), nearly abolishes the effects of light on this channel (Leszkiewicz & Aizenman, 2002). Expression of the γ 2S subunit along with the α 1 β 2 subunits decreases, but does not abolish, the redox sensitivity of the ion channel (Amato et al ., 1999; Pan et al ., 2000).…”