IDENTIFICATION OF MOLECULAR-COMPONENTS OF A-TYPE CHANNELS ACTIVATING AT SUBTHRESHOLD POTENTIALS

1. Xenopus oocytes injected with rat brain mRNA express a transient KC current similar to the A current that activates transiently near the threshold for Na+ action potential generation (I-SA) seen in somatic r ecordings from neurons. We used hybrid arrest with antisense oligonucl eotides to investigate which of the cloned K+ channel proteins might b e components of the channels responsible for the I-SA expressed from b rain mRNA. An oligonucleotide complementary to a sequence common to al l known mammalian Shal-related mRNAs [KV4.1, KV4.2, and KV4.3 (the nom enclature of Sh K+ channel genes of Chandy and colleagues was used in this paper)] blocked the expression of the I-SA. An oligonucleotide co mplementary only to the KV4.2 mRNA, the most abundant Shal-related tra nscript in rat brain RNA preparations, was also quite efficient in arr esting the expression of the I-SA from brain. These experiments indica te that Shal-related proteins are important components of the channels carrying the I-SA expressed in oocytes injected with brain mRNA. Howe ver, there are several significant differences between this I-SA and t he currents expressed in the same oocytes by in vitro transcribed KV4. 1 or KV4.2 cRNA. Most of these differences are eliminated if KV4.1 or KV4.2 cRNA is coinjected with brain poly-(A) RNA treated with antisens e oligonucleotides which arrest the expression of the I-SA, or with a 2-4Kb rat brain poly-(A) RNA fraction which does not express detectabl e K+ currents under the same recording conditions. These data support the hypothesis that I-SA channels such as those expressed from brain m RNA contain Shal proteins that can be modified by proteins encoded in RNAs that by themselves do not express K+ currents.