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A. Akopian, F. Mizuno; Glutamate Induces Cav1.3 L-type Ca Channel Internalization in Salamander Retinal Neurons. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3226.
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The functional activity of channels can be regulated (i) by changes in biophysical properties of the channel, and/or (ii) by alteration in the number of channels on the surface membrane. In the present study we investigated the effect of glutamate on the subcellular distribution of L-type Ca channels as a possible mechanism for glutamate-induced Ca current reduction in retinal neurons.
Whole-cell patch clamp technique, immunocytochemistry and confocal microscopy were used to study the effects of glutamate on Ca current and on the subcellular distribution of α1D (Cav1.3) L-type Ca channels in slice preparations and dissociated retinal neurons.
α1D labeling of cells in control solution was concentrated primarily on the surface membrane. Exposure of cells to glutamate increased cytoplasmic labeling, suggesting internalization of Ca channels. To quantify these changes we measured integrated fluorescence values in cytoplasmic (Fc), and a membrane (Fm) area and used Fc/Fm as a measure for internalization. The average ratio was increased from 0.6±0.5 in control, to 1.3±0.8 in cells exposed to glutamate. Further evidence for Ca channel internalization was provided by the use of myristoylated dynamin inhibitory peptide (DIP), an inhibitor of clathrine-mediated endocytosis. Pretreatment of cells with DIP dramatically reduced glutamate-induced Ca channel internalization. The average Fc/Fm reduced from 1.56±0.13% in untreated cells, to 0.53±0.05% in cells pretreated with DIP. In patch clamp experiments, pretreatment of slices with DIP attenuated the glutamate-induced inhibition of Ca currents, indicating the involvement of dynamin-dependent Ca channel endocytosis. Furthermore, we showed that F-actin stabilization attenuated glutamate-induced channel internalization, whereas disruption of F-actin caused internalization of Ca channels.
These data suggest that Cav1.3 channel internalization, which involves glutamate-induced Ca-dependent actin depolymerization, may serve as a possible mechanism for a reduction of L-type Ca currents by glutamate.
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