Objectives: 

The M-Current, formed by tetramerization of Kv7.2 and Kv7.3 subunits, is a neuronal voltage gated K+ current playing a key role in controlling resting potential and cell excitability. It has been described previously that the serum-and glucocorticoid regulated kinase 1 (SGK1) induces an increase Kv7.2/3 channels abundance in the membrane of Xenopus laevis oocytes. Recently, a neuronal isoform of this kinase (SGK1.1) has been shown to regulate neuronal ion channels. We aimed to study the regulation of the Kv7.2/3 current and the M current in various heterologous expression systems as well as in SCG neurons from a transgenic mouse expressing a constitutively active form of SGK1.1 (S515D).

Materials: 

KV7.2/3 currents were measured by TEVC on Xenopus oocytes, patch-clamp recordings on HEK293 transfected cells and neurons isolated from the superior cervical ganglia. Different mutations were introduced in the Kv7 channels and the kinase to investigate the underlying mechanism by site directed mutagenesis. Plasmids encoding different regulators were co transfected in cells using lipofectamine transfection methods. SCG neuron isolation was performed as previously described Lamas JA et al 2002, Neuroreport 13:585). Membrane abundance of Kv7.2/3 channels under different conditions was studied by flow cytometry analysis.

Results: 

An SGK1.1 mutant disrupting PIP2 binding (K21N/K22N/R23G) had no effect in the amplitude of the Kv7.2/3 current. SGK1.1 did not modify the voltage dependence and open or close kinetics of the Kv7.2/3 channels, suggesting that the kinase alters channel abundance in the membrane. We also tested M-current amplitude in neurons of the superior cervical ganglion (SCG) isolated from transgenic mice expressing a constitutively active form of SGK1.1 (S515D). Transgenic SCG neurons showed an increase in M-current amplitude, consistent with a trend towards a more negative resting potential and less excitability when compared with wild-type SCG neurons.

Conclusions: 

SGK1.1 is a novel regulator of M-channels that could be an integrator of different signal transduction pathways, controlling M-channels and therefore neuronal excitability.