Abstract 17570: Rescue of Dilated Cardiomyopathy in Nav1.5 Mutant Mice Defective in Calmodulin Binding by Inhibition of Late Na+ Current

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Hana Cho ◽  
Takeshi Aiba ◽  
Deborah DiSilvestre ◽  
Victoria Halperin ◽  
Eiki Takimoto ◽  
...  
Keyword(s):  
Heart Failure ◽  
Dilated Cardiomyopathy ◽  
Sodium Current ◽  
Ionic Currents ◽  
Na Channel ◽  
Binding Motif ◽  
Na Channels ◽  
Na Current ◽  
Down Regulation ◽  
K Currents

Introduction: Nav1.5, the main voltage-gated Na+ channel in the heart, has been shown to be involved in many cardiac diseases such as long QT syndrome, Brugada syndrome, and heart failure. Na+ channels are importantly regulated by Ca2+ calmodulin (CaM) mediated signaling: however, a fundamental understanding and physiological significance of CaM regulation of Na+ channel is incomplete. Here, we have created a transgenic mouse that harbors a mutated CaM binding motif (NaV1.5-IQ/AA), which is critical for Na+ channel regulation by Ca2+-CaM. Methods: Ventricle mass and function were analyzed with electrocardiogram, echocardiogram, and detailed invasive pressure-volume analysis. Additionally, single ventricular myocytes were obtained. Whole cell patch clamp was used to record membrane ionic currents, including sodium current, Ca2+ current, K+ currents and NCX current. Results: Homozygous mice are embryonic lethal and IQ/AA+/- mice exhibit a dramatic phenotype consisting of dilated cardiomyopathy (DCM) at 4-6 months of age with prolongation of QT. The Na+ current in IQ mice exhibits an enhanced slowly inactivating late component (INa,L) with concomitant up regulation of Na+/Ca2+ exchanger currents. Consistent with other models of DCM and heart failure, DCM in IQ/AA+/- mice was associated with a down regulation of transient outward K+ currents (Ito) and an increase in T-type Ca2+ currents. Chronic treatment with ranolazine designed to block INa,L prevented electrical remodeling of the hearts including an increase in INa,L and a down regulation of Ito. Consistent with the changes in INa,L and Ito, in ranolazine-fed IQ/AA+/- mice, the QT interval was decreased compared to vehicle (p<0.05). Further, the contractile dysfunction, cardiac hypertrophy, and myocardial fibrosis were attenuated in all ranolazine- fed animals, while ventricular dysfunction persisted in animals not fed drug (p<0.05). Conclusions: The data suggest that loss of CaM-mediated regulation of Na+ channel induces dilated cardiomyopathy by enhancing late Na+ current. Taken together, our data demonstrate a dynamic interplay for Ca2+ and Na+ signaling via the CaM binding motif of Na+ channels and highlight the critical importance of late Na+ currents to myopathy and arrhythmia.

scholarly journals The Combined Human Genotype of Truncating TTN and RBM20 Mutations Is Associated with Severe and Early Onset of Dilated Cardiomyopathy

Genes ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 883
Author(s):  
Anna Gaertner ◽  
Julia Bloebaum ◽  
Andreas Brodehl ◽  
Baerbel Klauke ◽  
Katharina Sielemann ◽  
...  
Keyword(s):  
Heart Failure ◽  
Dilated Cardiomyopathy ◽  
Early Onset ◽  
Target Genes ◽  
Frameshift Mutation ◽  
Rna Binding ◽  
Splicing Factor ◽  
Binding Motif ◽  
Rich Domain ◽  
Generation Sequencing

A major cause of heart failure is cardiomyopathies, with dilated cardiomyopathy (DCM) as the most common form. Over 40 genes are linked to DCM, among them TTN and RBM20. Next Generation Sequencing in clinical DCM cohorts revealed truncating variants in TTN (TTNtv), accounting for up to 25% of familial DCM cases. Mutations in the cardiac splicing factor RNA binding motif protein 20 (RBM20) are also known to be associated with severe cardiomyopathies. TTN is one of the major RBM20 splicing targets. Most of the pathogenic RBM20 mutations are localized in the highly conserved arginine serine rich domain (RS), leading to a cytoplasmic mislocalization of mutant RBM20. Here, we present a patient with an early onset DCM carrying a combination of (likely) pathogenic TTN and RBM20 mutations. We show that the splicing of RBM20 target genes is affected in the mutation carrier. Furthermore, we reveal RBM20 haploinsufficiency presumably caused by the frameshift mutation in RBM20.

Basis for tetrodotoxin and lidocaine effects on action potentials in dog ventricular myocytes

1988 ◽  
Vol 254 (6) ◽  
pp. H1157-H1166 ◽  
Author(s):  
J. A. Wasserstrom ◽  
J. J. Salata
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Ventricular Myocytes ◽  
Ionic Currents ◽  
Detectable Effect ◽  
Na Channel ◽  
Na Current ◽  
Voltage Range ◽  
Purkinje Fibers ◽  
Ventricular Cells

We studied the effects of tetrodotoxin (TTX) and lidocaine on transmembrane action potentials and ionic currents in dog isolated ventricular myocytes. TTX (0.1-1 x 10(-5) M) and lidocaine (0.5-2 x 10(-5) M) decreased action potential duration, but only TTX decreased the maximum rate of depolarization (Vmax). Both TTX (1-2 x 10(-5) M) and lidocaine (2-5 x 10(-5) M) blocked a slowly inactivating toward current in the plateau voltage range. The voltage- and time-dependent characteristics of this current are virtually identical to those described in Purkinje fibers for the slowly inactivating inward Na+ current. In addition, TTX abolished the outward shift in net current at plateau potentials caused by lidocaine alone. Lidocaine had no detectable effect on the slow inward Ca2+ current and the inward K+ current rectifier, Ia. Our results indicate that 1) there is a slowly inactivating inward Na+ current in ventricular cells similar in time, voltage, and TTX sensitivity to that described in Purkinje fibers; 2) both TTX and lidocaine shorten ventricular action potentials by reducing this slowly inactivating Na+ current; 3) lidocaine has no additional actions on other ionic currents that contribute to its ability to abbreviate ventricular action potentials; and 4) although both agents shorten the action potential by the same mechanism, only TTX reduces Vmax. This last point suggests that TTX produces tonic block of Na+ current, whereas lidocaine may produce state-dependent Na+ channel block, namely, blockade of Na+ current only after Na+ channels have already been opened (inactivated-state block).

scholarly journals Kinetic analysis of the action of Leiurus scorpion alpha-toxin on ionic currents in myelinated nerve.

1985 ◽  
Vol 86 (5) ◽  
pp. 739-762 ◽  
Author(s):  
G K Wang ◽  
G Strichartz
Keyword(s):  
Steady State ◽  
Ionic Currents ◽  
Na Channel ◽  
Dependent Manner ◽  
Na Current ◽  
Toxin Concentration ◽  
Toxin Molecule ◽  
Channel Inactivation ◽  
Na Currents ◽  
Voltage Dependent

The effects of a neurotoxin, purified from the venom of the scorpion Leiurus quinquestriatus, on the ionic currents of toad single myelinated fibers were studied under voltage-clamp conditions. Unlike previous investigations using crude scorpion venom, purified Leiurus toxin II alpha at high concentrations (200-400 nM) did not affect the K currents, nor did it reduce the peak Na current in the early stages of treatment. The activation of the Na channel was unaffected by the toxin, the activation time course remained unchanged, and the peak Na current vs. voltage relationship was not altered. In contrast, Na channel inactivation was considerably slowed and became incomplete. As a result, a steady state Na current was maintained during prolonged depolarizations of several seconds. These steady state Na currents had a different voltage dependence from peak Na currents and appeared to result from the opening of previously inactivated Na channels. The opening kinetics of the steady state current were exponential and had rates approximately 100-fold slower than the normal activation processes described for transitions from the resting state to the open state. In addition, the dependence of the peak Na current on the potential of preceding conditioning pulses was also dramatically altered by toxin treatment; this parameter reached a minimal value near a membrane potential of -50 mV and then increased continuously to a "plateau" value at potentials greater than +50 mV. The amplitude of this plateau was dependent on toxin concentration, reaching a maximum value equal to approximately 50% of the peak current; voltage-dependent reversal of the toxin's action limits the amplitude of the plateauing effect. The measured plateau effect was half-maximum at a toxin concentration of 12 nM, a value quite similar to the concentration producing half of the maximum slowing of Na channel inactivation. The results of Hill plots for these actions suggest that one toxin molecule binds to one Na channel. Thus, the binding of a single toxin molecule probably both produces the steady state currents and slows the Na channel inactivation. We propose that Leiurus toxin inhibits the conversion of the open state to inactivated states in a voltage-dependent manner, and thereby permits a fraction of the total Na permeability to remain at membrane potentials where inactivation is normally complete.

Sexual behaviour in Euplotes raikovi is accompanied by pheromone-induced modifications of ionic currents

1999 ◽  
Vol 202 (4) ◽  
pp. 475-483
Author(s):  
C. Stock ◽  
T. Krüppel ◽  
G. Key ◽  
W. Lueken
Keyword(s):  
Mating Type ◽  
Sexual Behaviour ◽  
Walking Speed ◽  
Ionic Currents ◽  
Marine Ciliate ◽  
Na Current ◽  
Threefold Increase ◽  
The Mean ◽  
Euplotes Raikovi ◽  
K Currents

In the marine ciliate Euplotes raikovi, pheromone released by a complementary mating type (nonself pheromone) induces typical sexual behaviour, whereas self pheromone released by the same mating type generally has no effect. Nonself pheromone evokes a reduction of the mean walking speed by 66 %, a threefold increase in the frequency and duration of long-lasting rest phases and a doubling in the number of side-stepping reactions. Consequently, translocation is strongly reduced and the cells remain in a small area. This could increase the probability of finding a sexual partner for pair formation (conjugation). The usual pattern of rhythmic, spontaneous depolarizations controlling the walking rhythm is absent in nonself-pheromone-stimulated cells. The remaining depolarizations arise from a 4 mV hyperpolarized membrane potential and do not reach the usual amplitudes of 15–20 mV but only of 6–10 mV. In addition, the amplitudes of K+ currents are increased at depolarizations of more than 20 mV by at least 30 %. Hyperpolarization- and depolarization-activated Na+ current amplitudes are increased, whereas the Ca2+ current amplitude remains nearly unaffected.

Is there a second external lidocaine binding site on mammalian cardiac cells?

1989 ◽  
Vol 257 (1) ◽  
pp. H79-H84 ◽  
Author(s):  
L. A. Alpert ◽  
H. A. Fozzard ◽  
D. A. Hanck ◽  
J. C. Makielski
Keyword(s):  
Binding Site ◽  
Cardiac Arrhythmias ◽  
Local Anesthetics ◽  
Sodium Current ◽  
Cardiac Cells ◽  
Na Channel ◽  
Functional Difference ◽  
Na Channels ◽  
Internal Perfusion ◽  
Cardiac Purkinje Cells

Lidocaine and its permanently charged analogue QX-314 block sodium current (INa) in nerve, and by this mechanism, lidocaine produces local anesthesia. When administered clinically, lidocaine prevents cardiac arrhythmias. Nerve and skeletal muscle are much more sensitive to local anesthetics when the drugs are applied inside the cell, indicating that the binding site for local anesthetics is located on the inside of those Na channels. Using a large suction pipette for voltage clamp and internal perfusion of single cardiac Purkinje cells, we demonstrate that a charged lidocaine analogue blocks INa not only when applied from the inside but also from the outside, unlike noncardiac tissue. This functional difference in heart predicts that a second local anesthetic binding site exists outside or near the outside of cardiac Na channels and emphasizes that the cardiac Na channel is different from that in nerve.

Cholinergic modulation of apical Na+ channels in turtle colon: analysis of CDPC-induced fluctuations

1990 ◽  
Vol 259 (4) ◽  
pp. C668-C674 ◽  
Author(s):  
D. J. Wilkinson ◽  
D. C. Dawson
Keyword(s):  
Single Channel ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Rate Coefficients ◽  
Corner Frequency ◽  
Na Channel ◽  
Fluctuation Analysis ◽  
Na Channels ◽  
Na Current

Current fluctuation analysis was used to investigate the properties of apical Na+ channels during muscarinic inhibition of active Na+ absorption. A reversible Na+ channel blocker, 6-chloro-3,5-diaminopyrazine-2-carboxamide (CDPC), was used to induce fluctuations in the short-circuit current (I(sc)). Power density spectra of the CDPC-induced fluctuations exhibited a clearly discernible Lorentzian component, characterized by a corner frequency that was linearly related to CDPC concentration between 20 and 100 microM. The on (k'on) and off (k(off)) rate coefficients for the CDPC blocking reaction were k'on = 11.1 +/- 0.8 rad.s-1.microM-1 and k(off) = 744 +/- 53 rad/s, and the microscopic inhibition constant was 67 microM (n = 11). CDPC blocking kinetics were not significantly different after inhibition of Isc by 5 microM serosal carbachol. Single-channel Na+ current (iNa) and the density of open and blocked Na+ channels (N(ob)) were estimated from the fluctuations induced by 40 microM CDPC. Under control conditions, iNa was 0.43 +/- 0.05 pA and N(ob) was 251 +/- 42 X 10(6)/cm2 (n = 10). After exposure to serosal carbachol (2-10 microM) for 60 min, Na+ current and N(ob) were reduced by approximately 50%, but iNa was not changed significantly. These results indicate that muscarinic inhibition of electrogenic Na+ absorption was associated with a reduction in the number of open Na+ channels in the apical membrane. They also suggest that this downregulation of transport involved a coordinated decrease in both apical and basolateral membrane conductances.

scholarly journals Abnormal Na channel gating in murine cardiac myocytes deficient in myotonic dystrophy protein kinase

2003 ◽  
Vol 12 (2) ◽  
pp. 147-157 ◽  
Author(s):  
Hwa C. Lee ◽  
Manoj K. Patel ◽  
Dilawaar J. Mistry ◽  
Qingcai Wang ◽  
Sita Reddy ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Current Density ◽  
Channel Gating ◽  
Resting Membrane Potential ◽  
Na Channel ◽  
Na Channels ◽  
Wild Type ◽  
Membrane Excitability ◽  
Na Current ◽  
Deficient Mice

DMPK is a serine/threonine kinase implicated in the human disease myotonic muscular dystrophy (DM). Skeletal muscle Na channels exhibit late reopenings in Dmpk-deficient mice and peak current density is reduced, implicating DMPK in regulation of membrane excitability. Since complete heart block and sudden cardiac death occur in the disease, we tested the hypothesis that cardiac Na channels also exhibit abnormal gating in Dmpk-deficient mice. We made whole cell and cell-attached patch clamp recordings of ventricular cardiomyocytes enzymatically isolated from wild-type, Dmpk+/−, and Dmpk−/− mice. Recordings from membrane patches containing one or a few Na channels revealed multiple Na channel reopenings occurring after the macroscopic Na current had subsided in both Dmpk+/− and Dmpk−/− muscle, but only rare reopenings in wild-type muscle (>3-fold difference, P < 0.05). This resulted in a plateau of non-inactivating Na current in Dmpk-deficient muscle. The magnitude of this plateau current was independent on the magnitude of the test potential from −40 to 0 mV and was also independent of gene dose. Macroscopic Na current density was similar in wild-type and Dmpk-deficient muscle, as was steady-state Na channel gating. Decay of macroscopic currents was slowed in Dmpk−/− muscle, but not in Dmpk+/− or wild-type muscle. Entry into, and recovery from, inactivation were similar at multiple test potentials in wild-type and Dmpk-deficient muscle. Resting membrane potential was depolarized, and action potential duration was significantly prolonged in Dmpk-deficient muscle. Thus in cardiac muscle, Dmpk deficiency results in multiple late reopenings of Na channels similar to those seen in Dmpk-deficient skeletal muscle. This is reflected in a plateau of non-inactivating macroscopic Na current and prolongation of cardiac action potentials.

scholarly journals Down-regulation of sodium current in heart failure: rescue by beta-blockers

2002 ◽  
Vol 39 ◽  
pp. 164
Author(s):  
Albertas I. Undrovinas ◽  
Victor A. Maltsev ◽  
Hani N. Sabbah
Keyword(s):  
Heart Failure ◽  
Sodium Current ◽  
Beta Blockers ◽  
Down Regulation

scholarly journals Phosphorylation of S1505 in the cardiac Na+ channel inactivation gate is required for modulation by protein kinase C.

1996 ◽  
Vol 108 (5) ◽  
pp. 375-379 ◽  
Author(s):  
Y Qu ◽  
J C Rogers ◽  
T N Tanada ◽  
W A Catterall ◽  
T Scheuer
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Na Channel ◽  
Na Channels ◽  
Na Current ◽  
Inactivation Curve ◽  
Electrophysiological Properties ◽  
Negative Shift ◽  
Kinase C ◽  
Steady State Inactivation

Inactivation of both brain and cardiac Na+ channels is modulated by activation of protein kinase C (PKC) but in different ways. Previous experiments had shown that phosphorylation of serine 1506 in the highly conserved loop connecting homologous domains III and IV (LIII/IV) of the brain Na+ channel alpha subunit is necessary for all effects of PKC. Here we examine the importance of the analogous serine for the different modulation of the rH1 cardiac Na+ channel. Serine 1505 of rH1 was mutated to alanine to prevent its phosphorylation, and the resulting mutant channel was expressed in 1610 cells. Electrophysiological properties of these mutant channels were indistinguishable from those of wild-type (WT) rH1 channels. Activation of PKC with 1-oleoyl-2-acetyl-sn-glycerol (OAG) reduced WT Na+ current by 49.3 +/- 4.2% (P &lt; 0.01) but S1505A mutant current was reduced by only 8.5 +/- 5.4% (P = 0.29) when the holding potential was -94 mV. PKC activation also caused a -17-mV shift in the voltage dependence of steady-state inactivation of the WT channel which was abolished in the mutant. Thus, phosphorylation of serine 1505 is required for both the negative shift in the inactivation curve and the reduction in Na+ current by PKC. Phosphorylation of S1505/1506 has common and divergent effects in brain and cardiac Na+ channels. In both brain and cardiac Na+ channels, phosphorylation of this site by PKC is required for reduction of peak Na+ current. However, phosphorylation of S1506 in brain Na+ channels slows and destabilizes inactivation of the open channel. Phosphorylation of S1505 in cardiac, but not S1506 in brain, Na+ channels causes a negative shift in the inactivation curve, indicating that it stabilizes inactivation from closed states. Since LIII/IV containing S1505/S1506 is completely conserved, interaction of the phosphorylated serine with other regions of the channel must differ in the two channel types.

LabHEART: an interactive computer model of rabbit ventricular myocyte ion channels and Ca transport

2001 ◽  
Vol 281 (6) ◽  
pp. C2049-C2060 ◽  
Author(s):  
José L. Puglisi ◽  
Donald M. Bers
Keyword(s):  
Heart Failure ◽  
Ionic Currents ◽  
Ventricular Myocyte ◽  
Original Formulation ◽  
Ca Current ◽  
Current Clamp ◽  
Interactive Computer Program ◽  
Intracellular Ca ◽  
On Line ◽  
K Currents

An interactive computer program, LabHEART, was developed to simulate the action potential (AP), ionic currents, and Ca handling mechanisms in a rabbit ventricular myocyte. User-oriented, its design allows switching between voltage and current clamp and easy on-line manipulation of key parameters to change the original formulation. The model reproduces normal rabbit ventricular myocyte currents, Ca transients, and APs. We also changed parameters to simulate data from heart failure (HF) myocytes, including reduced transient outward ( I to) and inward rectifying K currents ( I K1), enhanced Na/Ca exchange expression, and reduced sarcoplasmic reticulum Ca-ATPase function, but unaltered Ca current density. These changes caused reduced Ca transient amplitude and increased AP duration (especially at lower frequency) as observed experimentally. The model shows that the increased Na/Ca exchange current ( I NaCa) in HF lowers the intracellular [Ca] threshold for a triggered AP from 800 to 540 nM. Similarly, the decrease in I K1reduces the threshold to 600 nM. Changes in I tohave no effect. Combining enhanced Na/Ca exchange with reduced I K1 (as in HF) lowers the threshold to trigger an AP to 380 nM. These changes reproduce experimental results in HF, where the contributions of different factors are not readily distinguishable. We conclude that the triggered APs that contribute to nonreentrant ventricular tachycardia in HF are due approximately equally (and nearly additively) to alterations in I NaCa and I K1. A free copy of this software can be obtained at http://www.meddean.luc.edu/lumen/DeptWebs/physio/bers.html .

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