Faculty Bibliography

Our results demonstrate that (a) the Kir2.1 gene encodes a native K+ channel protein with a 21-pS conductance; (b) this channel has an important role in the genesis of adult ventricular 1K1; and (c) the contribution of Kir2.1 channel proteins to 1K1 changes during development. The lack of contribution of Kir2.1 to fetal 1K1 channels is interesting from the point of view of possible future generation of knockout mice lacking Kir2.1, since cardiac abnormalities would not be expected to result in fetal lethality. These observations provide further support for a generalized hypothesis that different genes may code for 1K1 channel proteins at various developmental stages. However, the effects of these AS-oligos must first be examined on native 1K1 channels in cardiac myocytes before definite conclusions can be reached

Potassium channels that are open at very negative membrane potentials govern the subthreshold behavior of neurons. These channels contribute to the resting potential and help regulate the degree of excitability of a neuron by affecting the impact of synaptic inputs and the threshold for action potential generation. They can have large influences on cell behavior even when present at low concentrations because few conductances are active at these voltages. We report the identification of a new K(+) channel pore-forming subunit of the ether-a-go-go (Eag) family, named Eag2, that expresses voltage-gated K(+) channels that have significant activation at voltages around -100 mV. Eag2 expresses outward-rectifying, non-inactivating voltage-dependent K(+) currents resembling those of Eag1, including a strong dependence of activation kinetics on prepulse potential. However, Eag2 currents start activating at subthreshold potentials that are 40-50 mV more negative than those reported for Eag1. Because they activate at such negative voltages and do not inactivate, Eag2 channels will contribute sustained outward currents down to the most negative membrane potentials known in neurons. Although Eag2 mRNA levels in whole brain appear to be low, they are highly concentrated in a few neuronal populations, most prominently in layer IV of the cerebral cortex. This highly restricted pattern of cortical expression is unlike that of any other potassium channel cloned to date and may indicate specific roles for this channel in cortical processing. Layer IV neurons are the main recipient of the thalamocortical input. Given their functional properties and specific distribution, Eag2 channels may play roles in the regulation of the behavioral state-dependent entry of sensory information to the cerebral cortex

Kv3.1 and Kv3.2 K(+) channel proteins form similar voltage-gated K(+) channels with unusual properties, including fast activation at voltages positive to -10 mV and very fast deactivation rates. These properties are thought to facilitate sustained high-frequency firing. Kv3.1 subunits are specifically found in fast-spiking, parvalbumin (PV)-containing cortical interneurons, and recent studies have provided support for a crucial role in the generation of the fast-spiking phenotype. Kv3.2 mRNAs are also found in a small subset of neocortical neurons, although the distribution of these neurons is different. We raised antibodies directed against Kv3.2 proteins and used dual-labeling methods to identify the neocortical neurons expressing Kv3.2 proteins and to determine their subcellular localization. Kv3.2 proteins are prominently expressed in patches in somatic and proximal dendritic membrane as well as in axons and presynaptic terminals of GABAergic interneurons. Kv3.2 subunits are found in all PV-containing neurons in deep cortical layers where they probably form heteromultimeric channels with Kv3.1 subunits. In contrast, in superficial layer PV-positive neurons Kv3.2 immunoreactivity is low, but Kv3.1 is still prominently expressed. Because Kv3.1 and Kv3.2 channels are differentially modulated by protein kinases, these results raise the possibility that the fast-spiking properties of superficial- and deep-layer PV neurons are differentially regulated by neuromodulators. Interestingly, Kv3. 2 but not Kv3.1 proteins are also prominent in a subset of seemingly non-fast-spiking, somatostatin- and calbindin-containing interneurons, suggesting that the Kv3.1-Kv3.2 current type can have functions other than facilitating high-frequency firing

Peptide growth factors such as the neurotrophins and fibroblast growth factors have potent effects on synaptic transmission, development, and cell survival. We report that chronic (hours) treatment with basic fibroblast growth factor (FGF-2) potentiates Ca(2+)-dependent N-methyl-D-aspartate (NMDA) receptor inactivation in cultured hippocampal neurons. This effect is specific for the NMDA-subtype of ionotropic glutamate receptor and FGF-2. The potentiated inactivation requires ongoing protein synthesis during growth factor treatment and the activity of protein phosphatase 2B (PP2B or calcineurin) during agonist application. These results suggest a mechanism by which FGF-2 receptor signaling may regulate neuronal survival and synaptic plasticity

Four mammalian Kv3 genes have been identified, each of which generates, by alternative splicing, multiple protein products differing in their C-terminal sequence. Products of the Kv3.1 and Kv3.2 genes express similar delayed-rectifier type currents in heterologous expression systems, while Kv3.3 and Kv3.4 proteins express A-type currents. All Kv3 currents activate relatively fast at voltages more positive than -10 mV, and deactivate very fast. The distribution of Kv3 mRNAs in the rodent CNS was studied by in situ hybridization, and the localization of Kv3.1 and Kv3.2 proteins has been studied by immunohistochemistry. Most Kv3.2 mRNAs (approximately 90%) are present in thalamic-relay neurons throughout the dorsal thalamus. The protein is expressed mainly in the axons and terminals of these neurons. Kv3.2 channels are thought to be important for thalamocortical signal transmission. Kv3.1 and Kv3.2 proteins are coexpressed in some neuronal populations such as in fast-spiking interneurons of the cortex and hippocampus, and neurons in the globus pallidus. Coprecipitation studies suggest that in these cells the two types of protein form heteromeric channels. Kv3 proteins appear to mediate, in native neurons, similar currents to those seen in heterologous expression systems. The activation voltage and fast deactivation rates are believed to allow these channels to help repolarize action potentials fast without affecting the threshold for action potential generation. The fast deactivating current generates a quickly recovering after hyperpolarization, thus maximizing the rate of recovery of Na+ channel inactivation without contributing to an increase in the duration of the refractory period. These properties are believed to contribute to the ability of neurons to fire at high frequencies and to help regulate the fidelity of synaptic transmission. Experimental evidence has now become available showing that Kv3.1-Kv3.2 channels play critical roles in the generation of fast-spiking properties in cortical GABAergic interneurons