Shal-type (Kv4.x) K+ channels are expressed in a variety of tissue, with particularly high levels in the brain and heart. These channels are the primary subunits that contribute to transient, voltage-dependent K+ currents in the nervous system (A currents) and the heart (transient outward current). Recent studies have revealed an enormous degree of complexity in the regulation of these channels. In this review, we describe the surprisingly large number of ancillary subunits and scaffolding proteins that can interact with the primary subunits, resulting in alterations in channel trafficking and kinetic properties. Furthermore, we discuss posttranslational modification of Kv4.x channel function with an emphasis on the role of kinase modulation of these channels in regulating membrane properties. This concept is especially intriguing as Kv4.2 channels may integrate a variety of intracellular signaling cascades into a coordinated output that dynamically modulates membrane excitability. Finally, the pathophysiology that may arise from dysregulation of these channels is also reviewed.

Consistent with our hypothesis, the presence of SDB was associated with an earlier age at cognitive decline. Our findings in CPAP+ participants suggest that CPAP treatment of SDB may delay progression of cognitive impairment.

Angelman syndrome (AS) is a disorder of human cognition characterized by severe mental retardation and epilepsy. Recently, a mouse model for AS (Ube3a maternal null mutation) was developed that displays deficits in both context-dependent learning and hippocampal long-term potentiation (LTP). In the present studies, we examined the molecular basis for these LTP and learning deficits. Mutant animals exhibited a significant increase in hippocampal phospho-calcium/calmodulin-dependent protein kinase II (CaMKII), specifically at sites Thr(286) and Thr(305), with no corresponding change in the levels of total CaMKII. In addition, mutants show a reduction in CaMKII activity, autophosphorylation capability, and total CaMKII associated with postsynaptic density. These findings are the first to implicate misregulation of CaMKII as a molecular cause for the neurobehavioral deficits in a human learning disorder.

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Calcium-calmodulin-dependent kinase II (CaMKII) has a long history of involvement in synaptic plasticity, yet little focus has been given to potassium channels as CaMKII targets despite their importance in repolarizing EPSPs and action potentials and regulating neuronal membrane excitability. We now show that Kv4.2 acts as a substrate for CaMKII in vitro and have identified CaMKII phosphorylation sites as Ser438 and Ser459. To test whether CaMKII phosphorylation of Kv4.2 affects channel biophysics, we expressed wild-type or mutant Kv4.2 and the K ϩ channel interacting protein, KChIP3, with or without a constitutively active form of CaMKII in Xenopus oocytes and measured the voltage dependence of activation and inactivation in each of these conditions. CaMKII phosphorylation had no effect on channel biophysical properties. However, we found that levels of Kv4.2 protein are increased with CaMKII phosphorylation in transfected COS cells, an effect attributable to direct channel phosphorylation based on site-directed mutagenesis studies. We also obtained corroborating physiological data showing increased surface A-type channel expression as revealed by increases in peak K ϩ current amplitudes with CaMKII phosphorylation. Furthermore, endogenous A-currents in hippocampal pyramidal neurons were increased in amplitude after introduction of constitutively active CaMKII, which results in a decrease in neuronal excitability in response to current injections. Thus CaMKII can directly modulate neuronal excitability by increasing cell-surface expression of A-type K ϩ channels.