Faculty Bibliography

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

The mammalian Kv4 gene subfamily and its Drosophila Shal counterpart encode proteins that form fast inactivating K+ channels that activate and inactivate at subthreshold potentials and recover from inactivation at a faster rate than other inactivating Kv channels. Taken together, the properties of Kv4 channels compare best with those of low-voltage activating 'A-currents' present in the neuronal somatodendritic compartment and widely reported across several types of central and peripheral neurons, as well as the (Ca2+-independent) transient outward potassium conductance of heart cells (Ito). Three distinct genes have been identified that encode mammalian Shal homologs (Kv4. 1, Kv4.2, and Kv4.3), of which the latter two are abundant in rat adult brain and heart tissues. The distribution in the adult rat brain of the mRNA transcripts encoding the three known Kv4 subunits was studied by in situ hybridization histochemistry. Kv4.1 signals are very faint, suggesting that Kv4.1 mRNAs are expressed at very low levels, but Kv4.2 and Kv4.3 transcripts appear to be abundant and each produces a unique pattern of expression. Although there is overlap expression of Kv4.2 and Kv4.3 transcripts in several neuronal populations, the dominant feature is one of differential, and sometimes reciprocal expression. For example, Kv4.2 transcripts are the predominant form in the caudate-putamen, pontine nucleus and several nuclei in the medula, whereas the substantia nigra pars compacta, the restrosplenial cortex, the superior colliculus, the raphe, and the amygdala express mainly Kv4.3. Some brain structures contain both Kv4.2 and Kv4.3 mRNAs but each dominates in distinct neuronal subpopulations. For example, in the olfactory bulb Kv4.2 dominates in granule cells and Kv4.3 in periglomerular cells. In the hippocampus Kv4.2 is the most abundant isoform in CA1 pyramidal cells, whereas only Kv4.3 is expressed in interneurons. Both are abundant in CA2-CA3 pyramidal cells and in granule cells of the dentate gyrus, which also express Kv4.1. In the dorsal thalamus strong Kv4.3 signals are seen in several lateral nuclei, whereas medial nuclei express Kv4.2 and Kv4.3 at moderate to low levels. In the cerebellum Kv4.3, but not Kv4.2, is expressed in Purkinje cells and molecular layer interneurons. In the cerebellar granule cell layer, the reciprocity between Kv4.2 and Kv4.3 is observed in subregions of the same neuronal population. In fact, the distribution of Kv4 channel transcripts in the cerebellum defines a new pattern of compartmentation of the cerebellar cortex and the first one involving molecules directly involved in signal processing