Epilepsy affects 0.5-1% of the population; however, it remains poorly understood and treatments are suboptimal. Understanding basic mechanisms underlying epilepsy is an important step in developing new treatments. We are pursuing post-translational modification of potassium (K ?) channels via phosphorylation as a candidate mechanism in epilepsy. K ? channels are critical determinants of neuronal excitability. K+ channel downregulation is associated with increased neuronal excitability and epilepsy phenotypes. Gene mutations or post-translational modifications, such as phosphorylation decrease functional K + channels. Indeed, phosphorylation of K ? channels could rapidly alter neuronal excitability and contribute to seizures; however, little is known about these mechanisms in epilepsy. This area of research has recently attracted national attention. At the 2003 American Epilepsy Society meeting, an entire symposium is dedicated to posttranslationalmodification through phosphorylation of ion channels as candidate mechanisms in epilepsy. Activation of the cyclic-AMP-dependent protein kinase (PKA) pathway in neurons increases excitability and epileptic discharges by decreasing the afterhyperpolarization (AHP) K ? current. The AHP current stops neuronal bursting and facilitates adaptation (slowing of firing frequency with sustained depolarization). Thus, the AHP restricts the spread of neuronal excitation, and downregulation of the AHP could contribute to increased excitability in epilepsy. The mechanism of PKA downregulation of the AHP current is unknown. Small-conductance K + channel (SK) subunits contribute to the AHP current. We propose direct PKA phosphorylation of SK channel subunits as a candidate molecular mechanism for modulation of the AHP K + current. In pilot studies we have identified several PKA phosphorylation sites in an SK subunit. Additionally we have EEG evidence that the SK blocker, apamin induces seizures in rats, suggesting that these channels may play a role in epilepsy.
The aims of this project are to characterize the PKA phosphorylation sites within SK proteins; evaluate the functional effects of phosphorylation of SK channels in expression systems; and investigate phosphorylation of SK channels in the kainate epilepsy model. Elucidating this form of post-translational modification of SK channels may guide drug development or gene therapy toward a novel target in epilepsy.
|Barnwell, L Forbes S; Lugo, Joaquin N; Lee, Wai L et al. (2009) Kv4.2 knockout mice demonstrate increased susceptibility to convulsant stimulation. Epilepsia 50:1741-51|