Intracellular Ca2+ oscillations induced by over-expressed CaV3.1 T-type Ca2+ channels in NG108-15 cells

Summary T-type Ca 2+ channel family includes three subunits Ca V 3.1, Ca V 3.2 and Ca V 3.3 and have been shown to control burst firing and intracellular Ca 2+ concentration ([Ca 2+ ] i ) in neurons. Here, we investigated whether Ca V 3.1 channels could generate a pacemaker current and contribute to cell excitability. Ca V 3.1 clones were over-expressed in the neuronal cell line NG108-15. Ca V 3.1 channel expression induced repetitive action potentials, generating spontaneous membrane potential oscillations (MPOs) and concomitant [Ca 2+ ] i oscillations. These oscillations were inhibited by T-type channels antagonists and were present only if the membrane potential was around −61 mV. [Ca 2+ ] i oscillations were critically dependent on Ca 2+ influx through Ca V 3.1 channels and did not involve Ca 2+ release from the endoplasmic reticulum. The waveform and frequency of the MPOs are constrained by electrophysiological properties of the Ca V 3.1 channels. The trigger of the oscillations was the Ca V 3.1 window current. This current induced continuous [Ca 2+ ] i increase at −60 mV that depolarized the cells and triggered MPOs. Shifting the Ca V 3.1 window current potential range by increasing the external Ca 2+ concentration resulted in a corresponding shift of the MPOs threshold. The hyperpolarization-activated cation current ( I h ) was not required to induce MPOs, but when expressed together with Ca V 3.1 channels, it broadened the membrane potential range over which MPOs were observed. Overall, the data demonstrate that the Ca V 3.1 window current is critical in triggering intrinsic electrical and [Ca 2+ ] i oscillations.