Biomedical subjects

Kirstine Calloe

Publications and source records attributed to Kirstine Calloe.

3 recordsLinked to original sources

PubMed2006

The acrylamide (S)-1 differentially affects Kv7 (KCNQ) potassium channels.

The family of Kv7 (KCNQ) potassium channels consists of five members. Kv7.2 and 3 are the primary molecular correlates of the M-current, but also Kv7.4 and Kv7.5 display M-current characteristics. M-channel modulators include blockers (e.g., linopirdine) for cognition enhancement and openers (e.g., retigabine) for treatment of epilepsy and neuropathic pain. We investigated the effect of a Bristol-Myers Squibb compound (S)-N-[1-(3-morpholin-4-yl-phenyl)-ethyl]-3-phenyl-acrylamide [(S)-1] on cloned human Kv7.1-5 potassium channels expressed in Xenopus laevis oocytes. Using two-electrode voltage-clamp recordings we found that (S)-1 blocks Kv7.1 and Kv7.1/KCNE1 currents. In contrast, (S)-1 produced a hyperpolarizing shift of the activation curve for Kv7.2, Kv7.2/Kv7.3, Kv7.4 and Kv7.5. Further, the compound enhanced the maximal current amplitude at all potentials for Kv7.4 and Kv7.5 whereas the combined activation/block of Kv7.2 and Kv7.2/3 was strongly voltage-dependent. The tryptophan residue 242 in S5, known to be crucial for the effect of retigabine, was also shown to be critical for the enhancing effect of (S)-1 and BMS204352. Furthermore, no additive effect on Kv7.4 current amplitude was observed when both retigabine and (S)-1 or BMS204352 were applied simultaneously. In conclusion, (S)-1 differentially affects the Kv7 channel subtypes and is dependent on a single tryptophan for the current enhancing effect in Kv7.4.

Acrylamides↗

PubMed2005

Hypoosmotic cell swelling as a novel mechanism for modulation of cloned HCN2 channels.

This work demonstrates cell swelling as a new regulatory mechanism for the cloned hyperpolarization-activated, cyclic nucleotide-gated channel 2 (HCN2). HCN2 channels were coexpressed with aquaporin1 in Xenopus laevis oocytes and currents were monitored using a two-electrode voltage-clamp. HCN2 channels were activated by hyperpolarization to -100 mV and the currents were measured before and during hypoosmotic cell swelling. Cell swelling increased HCN2 currents by 30% without changing the kinetics of the currents. Injection of 50 nl intracellular solution resulted in a current increase of 20%, indicating that an increase in cell volume also under isoosmotic conditions may lead to activation of HCN2. In the absence of aquaporin1 only negligible changes in oocyte cell volume occur during exposure to hypoosmotic media and no significant change in HCN2 channel activity was observed during perfusion with hypoosmotic media. This indicates that cell swelling and not a change in ionic strength of the media, caused the observed swelling-induced increase in current. The increase in HCN2 current induced by cell swelling could be abolished by cytochalasin D treatment, indicating that an intact F-actin cytoskeleton is a prerequisite for the swelling-induced current.

Actins↗

PubMed2005

Functional assessment of compound mutations in the KCNQ1 and KCNH2 genes associated with long QT syndrome.

BACKGROUND: Long QT syndrome (LQTS) is a cardiovascular disorder characterized by prolonged QTc time, syncope, or sudden death caused by torsades de pointes and ventricular fibrillation. We investigated the clinical and electrophysiologic phenotype of individual mutations and the compound mutations in a family in which different genotypes could be found. OBJECTIVES: The purpose of this study was to determine the impact of genotype-based diagnostic assessment in LQTS. METHODS: We used cascade screening and functional analyses to investigate the phenotype in a family with LQTS. The contributions of the compound mutations in the KCNQ1 and KCNH2 genes (KCNQ1 R591H, KCNH2 R328C) were analyzed by heterologous expression in Xenopus laevis oocytes using two-electrode voltage clamp and by confocal imaging. RESULTS: KCNH2 R328C did not show any functional phenotype whereas KCNQ1 R591H resulted in severe reduction of current. Neither wild-type nor mutant channels affected each other functionally in coexpression experiments. Therefore, a direct interaction between KCNQ1 and KCNH2 was ruled out under these conditions. CONCLUSION: Assessment of novel mutational findings in LQTS should include accurate genetic and functional analysis. Notably, appropriate studies are needed if two or more mutations in different genes are present in one proband. Our findings prompt reconsideration of the impact of compound mutations in LQTS families and reinforce the need for thorough functional evaluation of novel ion channel mutations before assignment of pathogenic status.

Alleles↗