1,721,014 research outputs found
Expression and function of dipeptidyl-aminopeptidase-like protein 6 (DPPX) as a putative b-subunit of human cardiac transient outward current encoded by Kv4.3
No full textDipeptidyl-aminopeptidase-like protein 6 (DPPX) was recently shown in the brain to modulate the kinetics of transient A-type currents by accelerating inactivation and recovery from inactivation. Since the kinetics of human cardiac transient outward current (I(to)) are not mimicked by coexpression of the alpha-subunit Kv4.3 with its known beta-subunit KChIP2, we have tested the hypothesis that DPPX may serve as an additional beta-subunit in the human heart. With quantitative real-time RT-PCR strong mRNA expression of DPPX was detected in human ventricles and was verified at the protein level in human but not in rat heart by a DPPX-specific antibody. Co-expression of DPPX with Kv4.3 in Chinese hamster ovary cells produced I(to)-like currents, but compared with expression of KChIP2a and Kv4.3, the time constant of inactivation was faster, the potential of half-maximum steady-state inactivation was more negative and recovery from inactivation was delayed. Co-expression of DPPX in addition to Kv4.3 and KChIP2a produced similar current kinetics as in human ventricular myocytes. We therefore propose that DPPX is an essential component of the native cardiac I(to) channel complex in human heart
Is SAP97 the main modulator of regulating Kv ion channels in dilated cardiomyopathy?
No full textBackground: Dilated cardiomyopathy is a multifactorial disease therefore it can be expected that
several gene expression is altered in the heart. The exact nature of those changes has not been
resolved yet. Voltage-dependent potassium channels regulate membrane excitability and cell communication
between cardiomyocytes. Cardiac ion channels are assembled as a homomeric and heteromeric
tetramers composed of a- and b-subunits providing the molecular basis for the
transmembrane ionic currents. The synapse-associated protein 97 (SAP97) can associate with different
potassium ion channels modulating and anchoring these proteins at the plasma membrane.
Aim and Methods: The aim of this study was to compare the expression of Kv ion channels and
the SAP97 in the cardiomyocytes of failing heart. We investigated the expression of the Kv ion channels
by molecular biological techniques (real-time qPCR and immunoblotting) in the heart of failing
and non-failing human ventricular preparations.
Results: The a-subunits of mRNA of channels did not change significantly or we measured mild upor
down-regulation. HERG and KvLQT1 were slightly up regulated but the KChIP2 gene significantly
decreased 50% as the MIRP4 in the left ventricle tissues of DCM patients comparing to those of
undiseased controls. Immunoblotting studies revealed that the protein expression of these
a-subunits is significantly decreased in the samples of patients.
Conclusion: DCM remodel the expression of delayed rectifier potassium channel genes and proteins.
Down-regulation was significant in the anchoring-subunits and little changed in the pore
forming a-subunits. The decreased SAP97 expression suggests that alterations in regulation of potassium
ion channel expression may play a main role in the development of pathological cardiac
repolarization in cardiomyopathy
Dpp10 - A New Putative Regulatory ß-subunit Of Ito In Failing And Non-failing Human Heart
No full textBackground: Recently we reported that the dipeptidyl-aminopeptidase-like protein DPP6 serves as a regulatory ß-subunit for cardiac Kv4.3 channels. DPP6 is up-regulated in human failing hearts in which Kv4.3 and the ß-subunit KChIP2 are down-regulated. Here, we provide evidence for the presence of a new member of this protein family, i.e. DPP10, in failing and non-failing human hearts and investigate the role of this putative ß-subunit in regulating transient outward current.
Methods: mRNA was extracted from samples of 5 failing and 5 non-failing human hearts and quantified by realtime PCR. Functional interaction of DPP10 and Kv4.3 was studied in co-expression experiments (Chinese hamster ovary CHO cells) with standard voltage clamp techniques.
Results: Expression level of DPP10 was 85±13 fg/ng in failing and 33±6 fg/ng total RNA in non-failing hearts (P<0.01), amounting to a 2.6fold reduction. In comparison, DPP6 was up-regulated 1.3fold (P<0.001). After co-expression of Kv4.3 and DPP10 in CHO cells, channel complexes were verified in the plasma membrane by immunostaining, suggesting proper trafficking as with co-expression of Kv4.3 and KChIP2. Expression of Kv4.3 alone failed to yield Ito current, but robust Ito amplitudes were measured after co-expression of Kv4.3 and DPP10, DDP6, or KChIP2. Compared with the conventional co-expression combination of Kv4.3 and KChIP2, kinetics of Ito inactivation were accelerated in Kv4.3 plus DPP10 channels ({tau}fast: 56± 3 ms and 5.9±0.4 ms, respectively; P<0.01), however, recovery from inactivation was not affected ({tau}rec: 53± 7 ms vs. 58±13 ms). Co-expression of Kv4.3 with KChIP2 plus DPP10 maintained rapid inactivation of Ito ({tau}fast 8±1ms), but enhanced recovery kinetics ({tau}rec: 13±2 ms, P<0.001). The role of glycosylation for channel kinetics was studied with the glycosylation inhibitor tunicamicin (10 μg/ml; 24h). In the presence of tunicamicin, Ito inactivation and recovery were slowed ({tau}fast 51± 4 ms and {tau}rec: 42±3 ms), suggesting importance of glycosylation for channel function. Kinetics were similarly slowed when extracellular domain of DDP10 was deleted ({tau}fast: 48±5 ms, {tau}rec: 30± 4 ms).
Conclusion: DPP10, like DPP6 and KChIP2, contributes to regulation of Ito in normal and diseased human hearts
Accessory subunits alter the temperature sensitivity of Kv4.3 channel complexes.
No full textIn human atrial myocytes the transient outward current I(to) develops a conspicuous faster inactivation with increasing temperatures. Since β-subunits are known to modulate I(to) current kinetics, we hypothesized that the temperature sensitivity of I(to) is not only determined by the property of the ion-passing α-subunit Kv4.3 but also by its interaction with accessory β-subunits. We therefore studied the influence of the transmembrane β-subunits KCNE1, KCNE2 and DPP6 on Kv4.3/KChIP2 channels in CHO cells at room temperature and at physiological temperature. Exposure to 37°C caused a significant acceleration of the channel kinetics, whereas current densities and voltage dependences remained unaltered at 37°C compared to 23°C. However, Kv4.3/KChIP2 channels without transmembrane β-subunits showed the strongest temperature sensitivity with considerably increased rates of activation and inactivation at 37°C. KCNE2 significantly slowed the current kinetics at 37°C compared to Kv4.3/KChIP2 channels, whereas KCNE1 did not influence the channel properties at both temperatures. Interestingly, the accelerating effects of DPP6 on current kinetics described at 23°C were diminished at physiological temperature, thus at 37°C current kinetics became remarkably similar for channel complexes Kv4.3/KChIP2 with and without DPP6 isoforms. A Markov state model was developed on the basis of experimental measurements to simulate the influence of β-subunits on Kv4.3 channel complex at both temperatures. In conclusion, the remarkably fast kinetics of the native I(to) at 37°C could be reproduced by co-expressing Kv4.3, KChIP2, KCNE2 and DPP6 in CHO cells, whereas the high temperature sensitivity of human I(to) could be not mimicked
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The transmembrane beta-subunits KCNE1, KCNE2, and DPP6 modify pharmacological effects of the antiarrhythmic agent tedisamil on the transient outward current Ito
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