Deletion of highly conserved C-terminal sequences in the Kv1 <tex>K^{+}$</tex> channel subfamily does not prevent expression of currents with wildtype characteristics

AbstractThe C-terminal regions of Kv1 K+ channels show little conservation between isoforms except for the last four C-terminal residues, (E/L)TDV, which are well conserved from Drosophila to man. Deletions of the 4,16, and 57 C-terminal residues of the human Kv1.5 channel did not affect whole cell current amplitude, midpoint of activation, degree of inactivation, or activation kinetics following expression in mouse L-cells. Similar results were obtained with the rat Kv1.1 channel. Therefore, the conserved (E/L)TDV motif, and most of the C-terminal amino acids, are not required for Kv1 channel expression

Mutations throughout the S6 region of the hKv1.5 channel alter the stability of the activation gate

First published September 21, 2001; 10.1152/ ajpcell.00232.2001.—The S6 segment of voltage-gated K+ channels is thought to contribute to the gate that opens the central permeation pathway. Here we present evidence that mutations throughout the cytoplasmic end of S6 strongly influence hKv1.5 channel gating characteristics. Modification of hKv1.5 at positions T505, V512, and S515 resulted in large negative shifts in the voltage dependence of activation, whereas modifications at position Y519 resulted in negative (Y519N) and positive (Y519F) shifts. When adjusted for the altered voltage sensitivity, activation kinetics of mutated channels were similar to those of the wild-type (WT) channel; however, deactivation kinetics of mutations T505I, T505V, V512A, and V512M [time constant (τ) = 35, 250, 170, and 420 ms, respectively] were still slower than WT (τ = 8.3 ms). In addition, deactivation of WT channels was highly temperature sensitive. However, deactivation of T505I and V512A channels was largely temperature insensitive. Together, these data suggest that mutations in S6 decouple activation from deactivation by altering the open-state stability and that residues on both sides of the highly conserved Pro-X-Pro sequence influence the movement of S6 during channel gating. </jats:p

Heteromultimeric assembly of human potassium channels: molecular basis of a transient outward current?

To gain insight into the molecular basis of cardiac repolarization, we have expressed K+ channels cloned from ventricular myocardium in Xenopus oocytes. A recently identified human cardiac K+ channel isoform (human Kv1.4) has properties similar to the 4-aminopyridine-sensitive calcium-insensitive component of the cardiac transient outward current. However, these channels recovered from inactivation much slower than native channels. Hybrid channels consisting of subunits from different K+ channel clones (delayed rectifier channels [Kv1.1, Kv1.2, and Kv1.5] and Kv1.4) were created by coinjection of cRNAs in oocytes. Multimeric channels consisting of Kv1.4:Kv1.1, Kv1.4:Kv1.2, and Kv1.4:Kv1.5 were expressed and compared. The hybrid channels displayed characteristics of heterotetrameric channels with kinetics that more closely resembled a native cardiac transient outward current. The inactivation and recovery from inactivation of the heteromeric channels indicated that the presence of a single inactivating subunit (Kv1.4) was probably sufficient to cause channel inactivation. The results demonstrate that expression of different K+ channel genes can produce channel protein subunits that assemble as heteromultimers with unique properties. It is shown that certain combinations of voltage-gated K+ channels probably do not contribute to native transient outward current. However, one combination of subunits could not be excluded. Therefore, this mechanism of channel assembly may underlie some of the functional diversity of potassium channels found in the cardiovascular system.</jats:p