MinK-Related Peptide 1

Abstract

Abstract-The HCN family of ion channel subunits underlies the currents I f in heart and I h and I q in the nervous system.In the present study, we demonstrate that minK-related peptide 1 (MiRP1) is a ␤ subunit for the HCN family. As such, it enhances protein and current expression as well as accelerating the kinetics of activation. Because MiRP1 also functions as a ␤ subunit for the cardiac delayed rectifier I Kr , these results suggest that this peptide may have the unique role of regulating both the inward and outward channels that underlie cardiac pacemaker activity. The full text of this article is available at http://www.circresaha.org. (Circ Res. 2001;88:e84-e87.)Key Words: HCN family Ⅲ MiRP1 Ⅲ KCNE family Ⅲ ␤ subunit T he HCN (hyperpolarization-activated cyclic nucleotidegated) family of ion channel subunits has been identified as the molecular correlate of the currents I f in heart and I h and I q in neurons. [1][2][3] However, several ion channels are heteromultimers of a large ␣ subunit (like the HCN family members) and smaller ␤ subunits. The cardiac delayed rectifiers I Kr 4 and I Ks 5 are examples of this basic principle. Their ␣ subunits derive from the ERG and KCNQ families, respectively, but both also contain ␤ subunits from the KCNE family of single transmembranespanning proteins called minK and minK-related peptides (MiRPs). In this study, we report that MiRP1 enhances the expression and speeds the kinetics of activation of the HCN family of channel subunits. From immunoprecipitation experiments, we show that it most probably forms a complex with HCN1. Using RNase protection assays (RPAs), we demonstrate that MiRP1 mRNA is prevalent in the primary cardiac pacemaking region, the sinoatrial (SA) node, and barely detectable in ventricle. Cardiac pacemaker activity is generated by a narrow balance of inward (I f ) and outward (I Kr ) currents. Our results demonstrate for the first time the potential importance of a single ␤ subunit in simultaneously regulating both the expression and gating of both inward and outward cardiac pacemaker channels. Materials and Methods Heterologous Expression in Xenopus OocytescRNA encoding mouse HCN1 or HCN2, rat MiRP1 with or without an HA tag at the carboxy-terminal, and rat minK were transcribed using the mMessage mMachine kit (Ambion). Xenopus laevis oocytes were isolated, injected with 2 to 5 ng (50 to 100 nL) of cRNA, and maintained in Barth medium at 18°C for 1 to 3 days. For experiments using both HCN1 or HCN2 and MiRP1 or minK, the respective cRNAs were injected in a 1:0.04 to 1 ratio. Electrophysiological studies on oocytes used the 2-microelectrode voltage clamp. The extracellular recording solution (OR2) contained, in mmol/L, NaCl 80, KCl 2, MgCl 2 1, and Na-HEPES 5 (pH 7.6). Group data are presented as meanϮSEM. Tests of statistical significance for midpoint and slope of activation curves were performed using unpaired Student's t tests. PϽ0.05 is considered significant. RNase Protection AssaysThe procedures for the preparation of total RNA from rabbit he...

A Potassium Channel-MiRP Complex Controls Neurosensory Function in Caenorhabditis elegans

“…Third, each subunit controls expression and/or stability of the other in neurons where both are expressed. Although the mps-1 knockdown effects on KVS-1 expression are consistent with previous observations showing that mammalian MiRPs alter protein expression levels of some pore-forming subunits (4,14,33), kvs-1 RNAi effect on MPS-1 protein levels is a novel observation suggesting that neither subunit is dispensable in physiological cell types in which a complex is programmed to be assembled. Fourth, in CHO cells KVS-1 forms functional channels whose characteristics are markedly altered upon co-expression with MPS-1.…”

“…A well-established characteristic of MiRPs is the capacity to associate with multiple pore-forming subunits in heterologous systems. For instance, MiRP1 can associate with HERG, KCNQ1, HCN, and Kv4.2 subunits (2,(13)(14)(15). Indeed, MiRP "promiscuity" has considerable biomedical implications, because, if a single MiRP coassembles with multiple pore-forming subunits, genetic mutations would be predicted to lead to disruption of multiple currents simultaneously.…”

The genetic basis of Brugada syndrome: A mutation update

“…The Kv:KCNE ion channel complexes are heterohexameric structures consisting of four a-subunits and two KCNE peptides [Morin and Kobertz, 2008]. The KCNE peptides modulate several potassium currents in the heart [Abbott and Goldstein, 2002;Abbott et al, 1999;Grunnet et al, 2003;Lewis et al, 2004;McCrossan et al, 2003;Yu et al, 2001;Zhang et al, 2001], including I Ks [Bendahhou et al, 2005], I Kr [Abbott and Goldstein, 2002], and possibly I to [Delpon et al, 2008]. The minK peptide, encoded by KCNE1, has been shown convincingly to confer a slow activation to the KCNQ1 channel, characteristic of the I Ks current, whereas the MiRP2:KCNQ1 complex is a constitutively active potassium channel [Schroeder et al, 2000].…”

IhChannels Contribute to the Different Functional Properties of Identified Dopaminergic Subpopulations in the Midbrain

“…Qualitative single-cell RT-mPCR experiments have shown that DA SN neurons coexpress three of the four I h channel subunits, HCN2, HCN3, and HCN4 (Franz et al, 2000). However, the molecular composition of native neuronal I h channels that might exist as homomeric or heteromeric complexes (Chen et al, 2001;Ulens and Tytgat, 2001;Yu et al, 2001) as well as the possible differential I h channel subunit expression between different DA subpopulations remains unclear. In this context, quantitative differences in HCN subunit expression might also play a significant role.…”