Cloning and tissue-specific expression of five voltage-gated potassium channel cDNAs expressed in rat heart.

Abstract

Five distinct K+ channel cDNA molecules (RK1 to RK5) were cloned from either rat heart or rat aorta cDNA libraries. Four of the channels, RK1 to RK4, are similar or identical to Shaker-like K+ channels previously identified in rat brain cDNA libraries. Major differences among RK1 to RK4 exist in the amino-and carboxyl-terminal regions and in amino acids representing potential extracellular sequence between the S1 and S2 hydrophobic domains. RK5 encodes a unique channel of 490 amino acids having six hydrophobic domains but only five basic residues in the putative voltagesensing domain. Unlike RK1 to RK4, RK5 is a rat homologue of the Drosophila Shal family of K+ channels, which have not been previously described in mammals. Although RK5 mRNA is present in cardiac atrium and ventricle, it is most abundant in brain. RK1, RK2, and RK3 transcripts are predominantly found in brain but are present also at lower levels in other tissues, such as heart and aorta. RK2 is absent from skeletal muscle whereas RK1 and RK3 are present in this tissue. RK4 mRNA is ubiquitous in electrically excitable tissue, being present at comparable levels in atrium, ventricle, aorta, brain, and skeletal muscle. The cloning of RK5 confirms the presence in mammals of all four Drosophila K+ channel families: Shaker, Shab, Shaw, and Shal.Potassium channels constitute the most diverse group of voltage-gated ion channels. At least four general classes of K+ channels have been defiuied by electrophysiological means, with each class being comprised of many subtypes.These classes include inward rectifiers, Ca2+-activated K+ channels, A-type K+ channels, and delayed rectifiers (1). This diversity of K+ channel electrophysiology suggests that these channels are also structurally diverse. The discovery of a Drosophila strain possessing a mutant K+ channel prompted the cloning of the Drosophila Shaker gene (2), initiating the study of K+ channels at the molecular level. To date, the complete cDNA sequences for 1 mouse (3), 2 human (4, 5), and 11 rat (6-15) K+ channel cDNA clones have been reported. Heterogeneity in mammals appears to be generated primarily by the expression of a large number of genes, since known mammalian K+ channel genes are intronless (4,5,12,14,16) and alternative splicing in mammals has not been reported.Whereas previous K+ channel cloning efforts have focused on the nervous system, this paper reports the sequence and tissue distribution of five K+ channel clones (RK1 to RK5) from the rat cardiovascular system.t RK1 to RK4 are homologues of the Drosophila Shaker K+ channel family. RK5 has not been described previously, to our knowledge, and is a mammalian homologue of the Drosophila Shal gene. This study further illustrates the diversity of structure and tissuespecific expression of mammalian K+ channels.MATERIALS AND METHODS cDNA Library Construction and Screening. Size-fractionated libraries [2-to 8-kilobase (kb) cDNA] were constructed according to standard protocols (17). PCR-generated cDNA fragments corresponding to nucle...

Molecular correlates of the calcium‐independent, depolarization‐activated K+ currents in rat atrial myocytes

“…The results of the experiments presented here demonstrate that AsODNs targeted against three of the Kv á subunits expressed in rat heart Kv1.2, Kv1.5 and Kv4.2 (Roberds & Tamkun, 1991;Dixon & McKinnon, 1994;Barry et al 1995;Xu et al 1996) attenuate peak outward K¤ current amplitudes recorded in isolated P28 rat atrial myocytes. Although current amplitudes (densities) in control and AsODN-treated P28 rat atrial myocytes vary considerably among cells, on average, peak outward current densities were reduced approximately 30% in cells exposed to the AsODNs (Table 3).…”

“…The experiments here were undertaken to test directly the hypothesis that different Kv á channel subunits underlie IK,fast, IK,slow and Iss in rat atrial myocytes. In these experiments, the effects of antisense oligodeoxynucleotides targeted against the translation start sites of several Kv á subunits expressed in rat atria, Kv1.2, Kv1.5, Kv2.1, Kv4.2 and Kv4.3 (Roberds & Tamkun, 1991;Dixon & McKinnon, 1994;Barry et al 1995;, were examined. The results presented reveal that distinct Kv channel á subunits, Kv4.2, Kv1.2 and Kv1.5, contribute to IK,fast, IK,slow, and Iss, respectively, in adult rat atrial myocytes.…”

Effects of Oxypeucedanin on hKv1.5 and Action Potential Duration

“…However, there are several reports suggesting that Kv1.5 channel is expressed in both rat atrial and ventricular myocyte. [17][18][19] Thus, although we did not do experiment with human heart due to the difficulty to get its sample, the effect of oxypeucedanin on human heart might be the same with that on rat heart.…”

“…The action potentials were recorded with a 3-M KClfilled microelectrode (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) connected to an amplifier (KS-700, WPI), and they were displayed on an oscilloscope (dual-beam storage 5113, Tektronix, Beaverton, OR, U.S.A.). The tracings on the oscilloscope screen were photographed using 35-mm film, and they also recorded on a chart recorder (RS 3400, Gould, Cleveland, OH, U.S.A.).…”

Viral vector-mediated expression of K+ channels regulates electrical excitability in skeletal muscle

“…15 Expression of Kv1.4 has been shown in heart and brain, but not skeletal muscle. 18 The introduction of an exogenous Kv1.4 channel would be expected to change both the total amount of K + current and the characteristics of the current with respect to voltage and time dependence of activation and inactivation.…”