Faculty Bibliography

External application of hydrogen peroxide (H2O2) was found to inhibit the time-dependent fast inactivation process of three cloned voltage-gated K+ channels expressed in Xenopus oocytes: KShIIIC, KShIIID and HukII. As expected from kinetic models where some channels are still opening while a significant fraction of channels is already inactivated there was a large increase in current magnitude concomitant to inactivation block. The channels otherwise functioned normally. The effects of H2O2 were specific (other cloned voltage-gated K+ channels were not affected), and reversible, the currents returned to normal upon removal of the H2O2. H2O2 is produced during normal metabolism; it could act as a modulator of excitability through effects on K+ channels if effective local concentrations are reached in neuronal regions close to the channel. KShIIIC and KShIIID currents are very similar to an O2-sensitive K+ current present in type I cells of the carotid body which is believed to underlie the modulation of excitability of these cells by changes in arterial O2 pressure. H2O2 has been proposed as an intermediary between O2 and cellular response in the carotid body; our results provide support for this model

Northern blot analysis and in situ hybridization studies reveal the highly localized expression in rat brain of transcripts from a gene (KShIIIA) encoding components for voltage-gated K+ channels. KShIIIA expression is particularly prominent throughout the dorsal thalamus. The expression of KShIIIA is compared to that of a closely related gene, here called NGK2-KV4. These two genes encode transcripts that induce currents in Xenopus oocytes that are as of yet indistinguishable, but they show very different patterns of expression in rat brain. NGK2-KV4 transcripts are particularly abundant in the cerebellar cortex, where KShIIIA expression is very weak. These results demonstrate the existence of cell-type-specific K+ channel components and suggest that one reason for the unusually large diversity of K+ channel proteins is the presence of subtypes that participate in specific brain functions

Transient voltage-dependent potassium (K+) currents, also known as A currents, have been of great interest to neurophysiologists due to their special roles in neuronal excitability. Several cDNAs encoding transcripts expressing A currents have been characterized. Recently, a cDNA (KShIIIC or Raw3) was isolated which expresses an unusual A current that is highly sensitive to TEA, and activates at potentials more positive than -20 mV. Channels containing this protein may have specialized roles in modulating the electrical behaviour of neurons. Here we report the isolation and characterization of two rat cDNAs corresponding to two alternatively spliced transcripts (KShIIID.1 and KShIIID.2) from another gene (KShIIID) of the same subfamily as KShIIIC, the ShIII or Shaw-related gene subfamily. KShIIID.1 also expresses an unusual high-voltage-activating, TEA-sensitive A-type channel. There are, however, significant differences between KShIIIC and KShIIID channels which may have interesting functional consequences. The two most important differences are: (i) KShIIID channels conduct in the steady-state over a much broader window of potentials than KShIIIC; this reflects differences between the kinetic schemes of the two channels; and (ii) KShIIID inactivates with significantly slower kinetics than KShIIIC. The identification of KShIIID transcripts contributes to our knowledge of the molecular components that may determine the functional diversity of A currents and provides exciting opportunities to increase our understanding of the structure and function of K+ channels