Human neuronal stargazin-like proteins, γ(2), γ(3 )and γ(4); an investigation of their specific localization in human brain and their influence on Ca(V)2.1 voltage-dependent calcium channels expressed in Xenopus oocytes.

BACKGROUND: Stargazin (γ(2)) and the closely related γ(3), and γ(4 )transmembrane proteins are part of a family of proteins that may act as both neuronal voltage-dependent calcium channel (VDCC) γ subunits and transmembrane α-amino-3-hydroxy-5-methyl-4-isoxazoleproponinc (AMPA) receptor regulatory proteins (TARPs). In this investigation, we examined the distribution patterns of the stargazin-like proteins γ(2), γ(3), and γ(4 )in the human central nervous system (CNS). In addition, we investigated whether human γ(2 )or γ(4 )could modulate the electrophysiological properties of a neuronal VDCC complex transiently expressed in Xenopus oocytes. RESULTS: The mRNA encoding human γ(2 )is highly expressed in cerebellum, cerebral cortex, hippocampus and thalamus, whereas γ(3 )is abundant in cerebral cortex and amygdala and γ(4 )in the basal ganglia. Immunohistochemical analysis of the cerebellum determined that both γ(2 )and γ(4 )are present in the molecular layer, particularly in Purkinje cell bodies and dendrites, but have an inverse expression pattern to one another in the dentate cerebellar nucleus. They are also detected in the interneurons of the granule cell layer though only γ(2 )is clearly detected in granule cells. The hippocampus stains for γ(2 )and γ(4 )throughout the layers of the every CA region and the dentate gyrus, whilst γ(3 )appears to be localized particularly to the pyramidal and granule cell bodies. When co-expressed in Xenopus oocytes with a Ca(V)2.1/β(4 )VDCC complex, either in the absence or presence of an α2δ(2 )subunit, neither γ(2 )nor γ(4 )significantly modulated the VDCC peak current amplitude, voltage-dependence of activation or voltage-dependence of steady-state inactivation. CONCLUSION: The human γ(2), γ(3 )and γ(4 )stargazin-like proteins are detected only in the CNS and display differential distributions among brain regions and several cell types in found in the cerebellum and hippocampus. These distribution patterns closely resemble those reported by other laboratories for the rodent orthologues of each protein. Whilst the fact that neither γ(2 )nor γ(4 )modulated the properties of a VDCC complex with which they could associate in vivo in Purkinje cells adds weight to the hypothesis that the principal role of these proteins is not as auxiliary subunits of VDCCs, it does not exclude the possibility that they play another role in VDCC function.