Tissue-specific Expression and Gabapentin-Binding Properties of Calcium Channel α2δ Subunit Subtypes
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We report here the tissue-specific expression and gabapentin-binding properties of calcium channel α2δ subunits. Northern blot analysis demonstrated that human α2δ-1, -2, and -3 mRNA all had high levels of expression in brain, heart and skeletal muscle. However, the highest expression of human α2δ-2 mRNA was found in lung. Human α2δ-1, -2, and -3 mRNAs were detected in all portions of brain tested. Western blotting revealed that α2δ-2 protein was predominantly expressed in cerebellar cortex (brain) and undetectable in lung. The dissociation between mRNA and protein levels of human α2δ-2 in lung suggests possible post-transcriptional regulation. Although mouse α2δ-1 proteins exhibited a similar tissue distribution profile as that of human, tissue distribution of mouse α2δ-2 and -3 mRNA revealed a different profile. Mouse α2δ-3 mRNA was restricted to brain and mouse α2δ-2 mRNA was not detectable in lung. Gel electrophoresis under a reduced condition resulted in a mobility shift of both α2δ-1 and α2δ-2 proteins, suggesting that α2 and δ of α2δ-2 protein are linked by disulfide bond as are α2 and δ of α2δ-1. Scatchard plots revealed a single population of gabapentin binding sites for human α2δ-2 with the KD value twofold higher than that of porcine α2δ-1 (156 ± 25 nm vs. 72 ± 9 nm). Inhibition of gabapentin binding to α2δ-2 by selected amino acids and gabapentin analogs produced a binding profile similar, but not identical to that of α2δ-1.
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