The effect of overexpression of auxiliary Ca2+ channel subunits on native Ca2+ channel currents in undifferentiated mammalian NG108-15 cells

• Published in: The Journal of physiology Vol. 510; no. 2; pp. 347 - 360
• Main Authors: Wyatt, Christopher N., Page, Karen M., Berrow, Nicholas S., Brice, Nicola L., Dolphin, Annette C.
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 15-07-1998; Blackwell Science Ltd; Blackwell Science Inc
• Subjects: Animals; Brain Neoplasms - metabolism; Calcium Channels - biosynthesis; Calcium Channels - genetics; Calcium Channels - metabolism; Electric Stimulation; Electrophysiology; Glioma - metabolism; Hybrid Cells; Immunohistochemistry; Ion Channel Gating - physiology; Membrane Potentials - physiology; Mice; Neuroblastoma - metabolism; Original; Patch-Clamp Techniques; Rats; Reverse Transcriptase Polymerase Chain Reaction; Transfection
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.1998.347bk.x

High voltage activated (HVA) Ca 2+ channels are composed of a pore-forming α1 subunit and the accessory β and α2–δ subunits. However, the subunit composition
of low voltage activated (LVA), or T-type, Ca 2+ channels has yet to be elucidated. We have examined whether native calcium channels in NG108-15 mouse neuroblastoma × rat
glioma hybrid cells, which express predominantly LVA currents when undifferentiated, are modulated by overexpression of accessory
calcium channel subunits.
Endogenous α1A, B, C, D and E, and low levels of β and α2–δ subunit protein were demonstrated in undifferentiated NG108-15
cells.
The α2–δ, β2a or β1b accessory subunits were overexpressed by transfection of the cDNAs into these cells, and the effect examined
on the endogenous Ca 2+ channel currents. Heterologous expression, particularly of α2–δ but also of β2a subunits clearly affected the profile of
these currents. Both subunits induced a sustained component in the currents evoked by depolarizing voltages above −30 mV,
and α2–δ additionally caused a depolarization in the voltage dependence of current activation, suggesting that it also affected
the native T-type currents. In contrast, β1b overexpression had no effect on the endogenous Ca 2+ currents, despite immunocytochemical evidence for its expression in the transfected cells.
These results suggest that in NG108-15 cells, overexpression of the Ca 2+ channel accessory subunits α2–δ and β2a induce a sustained component of HVA current, and α2–δ also influences the voltage
dependence of activation of the LVA current. It is possible that native T-type α1 subunits are not associated with β subunits.