Faculty Bibliography

K+ channel principal subunits are by far the largest and most diverse of the ion channels. This diversity originates partly from the large number of genes coding for K+ channel principal subunits, but also from other processes such as alternative splicing, generating multiple mRNA transcripts from a single gene, heteromeric assembly of different principal subunits, as well as possible RNA editing and posttranslational modifications. In this chapter, we attempt to give an overview (mostly in tabular format) of the different genes coding for K+ channel principal and accessory subunits and their genealogical relationships. We discuss the possible correlation of different principal subunits with native K+ channels, the biophysical and pharmacological properties of channels formed when principal subunits are expressed in heterologous expression systems, and their patterns of tissue expression. In addition, we devote a section to describing how diversity of K+ channels can be conferred by heteromultimer formation, accessory subunits, alternative splicing, RNA editing and posttranslational modifications. We trust that this collection of facts will be of use to those attempting to compare the properties of new subunits to the properties of others already known or to those interested in a comparison between native channels and cloned candidates

The activation of T-lymphocytes is dependent upon, and accompanied by, an increase in voltage-gated K+ conductance. Kv1.3, a Shaker family K+ channel protein, appears to play an essential role in the activation of peripheral human T cells. Although Kv1.3-mediated K+ currents increase markedly during the activation process in mice, and to a lesser degree in humans, Kv1.3 mRNA levels in these organisms do not, indicating post-transcriptional regulation. In other tissues Shaker K+ channel proteins physically associate with cytoplasmic beta-subunits (Kvbeta1-3). Recently it has been shown that Kvbeta1 and Kvbeta2 are expressed in mouse T cells and that they are up-regulated during mitogen-stimulated activation. In this study, we show that the human Kvbeta subunits substantially increase K+ current amplitudes when coexpressed with their Kv1.3 counterpart, and that unlike in mouse, protein levels of human Kvbeta2 remain constant upon activation. Differences in Kvbeta2 expression between mice and humans may explain the differential K+ conductance increases which accompany T-cell proliferation in these organisms

Fast-spiking GABAergic interneurons of the neocortex and hippocampus fire high-frequency trains of brief action potentials with little spike-frequency adaptation. How these striking properties arise is unclear, although recent evidence suggests K(+) channels containing Kv3.1-Kv3.2 proteins play an important role. We investigated the role of these channels in the firing properties of fast-spiking neocortical interneurons from mouse somatosensory cortex using a pharmacological and modeling approach. Low tetraethylammonium (TEA) concentrations (</=1 mM), which block only a few known K(+) channels including Kv3.1-Kv3.2, profoundly impaired action potential repolarization and high-frequency firing. Analysis of the spike trains evoked by steady depolarization revealed that, although TEA had little effect on the initial firing rate, it strongly reduced firing frequency later in the trains. These effects appeared to be specific to Kv3.1 and Kv3.2 channels, because blockade of dendrotoxin-sensitive Kv1 channels and BK Ca(2+)-activated K(+) channels, which also have high TEA sensitivity, produced opposite or no effects. Voltage-clamp experiments confirmed the presence of a Kv3.1-Kv3.2-like current in fast-spiking neurons, but not in other interneurons. Analysis of spike shape changes during the spike trains suggested that Na(+) channel inactivation plays a significant role in the firing-rate slowdown produced by TEA, a conclusion that was supported by computer simulations. These findings indicate that the unique properties of Kv3.1-Kv3.2 channels enable sustained high-frequency firing by facilitating the recovery of Na(+) channel inactivation and by minimizing the duration of the afterhyperpolarization in neocortical interneurons

The cardiac inward rectifying K+ current (IK1) is important in maintaining the maximum diastolic potential. We used antisense oligonucleotides to determine the role of Kir2.1 channel proteins in the genesis of native rat ventricular IK1. A combination of two antisense phosphorothioate oligonucleotides inhibited heterologously expressed Kir2.1 currents in Xenopus oocytes, either when coinjected with Kir2.1 cRNA or when applied in the incubation medium. Specificity was demonstrated by the lack of inhibition of Kir2.2 and Kir2.3 currents in oocytes. In rat ventricular myocytes (4-5 days culture), these oligonucleotides caused a significant reduction of whole cell IK1 (without reducing the transient outward K+ current or the L-type Ca2+ current). Cell-attached patches demonstrated the occurrence of multiple channel events in control myocytes (8, 14, 21, 35, 43, and 80 pS). The 21-pS channel was specifically knocked down in antisense-treated myocytes (fewer patches contained this channel, and its open frequency was reduced). These results demonstrate that the Kir2.1 gene encodes a specific native 21-pS K(+)-channel protein and that this channel has an essential role in the genesis of cardiac IK1