Localised Ca channel phosphorylation modulates the distribution of L-type Ca current in cardiac myocytes

2010 ◽  
Vol 49 (1) ◽  
pp. 121-131 ◽  
Author(s):  
Anabelle Chase ◽  
John Colyer ◽  
Clive H. Orchard
Keyword(s):  
Cardiac Myocytes ◽  
Ca Channel ◽  
Ca Current

Sodium-calcium exchange-mediated contractions in feline ventricular myocytes

1992 ◽  
Vol 263 (4) ◽  
pp. H1161-H1169 ◽  
Author(s):  
H. B. Nuss ◽  
S. R. Houser
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Membrane Potentials ◽  
Exchange Mechanism ◽  
Ca Channel ◽  
Ca Current ◽  
Voltage Step ◽  
Reverse Mode ◽  
Sodium Calcium ◽  
Calcium Exchange

The hypothesis that Ca entry by the sarcolemmal Na-Ca exchange mechanism induces sarcoplasmic reticulum (SR) Ca release, loads the SR with Ca, and/or directly induces contractions by elevating cytosolic free Ca was tested in voltage-clamped feline ventricular myocytes. Intracellular Na concentration was increased by cellular dialysis to enhance Ca influx via "reverse-mode" Na-Ca exchange at positive membrane potentials, at which the "L-type" Ca current (ICa) should be small. Contractions were induced in the presence of Ca channel antagonists by depolarization to these potentials, suggesting that Ca influx via reverse-mode Na-Ca exchange was involved. These contractions had both phasic (SR related) and tonic components of shortening. They were smaller and began with more delay after depolarization than contractions which involved ICa. The magnitude of shortening was graded by the amount and duration of depolarization, suggesting that Ca influx via reverse-mode Na-Ca exchange has the capacity to induce and grade SR Ca release. Small slow contractions could be evoked in the presence of ryanodine (to impair SR function) and verapamil (to block ICa), supporting the idea that Ca influx via Na-Ca exchange is sufficient to directly activate the contractile proteins. Contractions induced by voltage steps to +10 mV, which were usually small when ICa was blocked, were potentiated if preceded by a voltage step to strongly positive potentials. This potentiation was inhibited by ryanodine, suggesting that Ca entry that occurs by Na-Ca exchange may be important for normal SR Ca loading.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Antibodies to the ciliary membrane of Paramecium tetraurelia alter membrane excitability.

1983 ◽  
Vol 97 (5) ◽  
pp. 1421-1428 ◽  
Author(s):  
R Ramanathan ◽  
Y Saimi ◽  
J B Peterson ◽  
D L Nelson ◽  
C Kung
Keyword(s):  
Antibody Binding ◽  
Voltage Sensitivity ◽  
Ca Channel ◽  
Paramecium Tetraurelia ◽  
Membrane Excitability ◽  
Ca Current ◽  
Antibody Treatment ◽  
Ciliary Membrane ◽  
Entire Cell ◽  
Electrophysiological Effects

Immobilization of Paramecium followed the binding of antibodies to the major proteins of the ciliary membrane (the immobilization antigens, i-antigens, approximately 250,000 mol wt). Immunoelectron microscopy showed this binding to be serotype-specific and to occur over the entire cell surface. Antibody binding also reduced the current through the Ca-channel of the excitable ciliary membrane as monitored using a voltage-clamp. The residual Ca-current appeared normal in its voltage sensitivity and kinetics. As a secondary consequence of antibody binding, the Ca-induced K-current was also reduced. The resting membrane characteristics and other activatable currents, however, were not significantly altered by the antibody treatment. Since monovalent fragments of the antibodies also reduced the current but did not immobilize the cell, the electrophysiological effects were not the secondary consequences of immobilization. Antibodies against the second most abundant family of proteins (42,000-45,000 mol wt) had similar electrophysiological effects as revealed by experiments in which the Paramecia and the serum were heterologous with respect to the i-antigen but homologous with respect to the 42,000-45,000-mol-wt proteins. Protease treatment, shown to remove the surface antigen, also caused a reduction of the Ca-inward current. The loss of the inward Ca-current does not seem to be due to a drop in the driving force for Ca++ entry since increasing the external Ca++ or reducing the internal Ca++ (through EGTA injection) did not restore the current. Here we discuss the possibilities that (a) the major proteins define the functional environment of the Ca-channel and that (b) the Ca-channel is more susceptible to certain general changes in the membrane.

scholarly journals Properties of L-type calcium channel gating current in isolated guinea pig ventricular myocytes.

1991 ◽  
Vol 98 (2) ◽  
pp. 265-285 ◽  
Author(s):  
R W Hadley ◽  
W J Lederer
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Channel Gating ◽  
Charge Movement ◽  
Ca Channel ◽  
Dependent Manner ◽  
Gating Current ◽  
Ca Current ◽  
Channel Inactivation ◽  
Time Dependencies

Nonlinear capacitative current (charge movement) was compared to the Ca current (ICa) in single guinea pig ventricular myocytes. It was concluded that the charge movement seen with depolarizing test steps from -50 mV is dominated by L-type Ca channel gating current, because of the following observations. (a) Ca channel inactivation and the immobilization of the gating current had similar voltage and time dependencies. The degree of channel inactivation was directly proportional to the amount of charge immobilization, unlike what has been reported for Na channels. (b) The degree of Ca channel activation was closely correlated with the amount of charge moved at all test potentials between -40 and +60 mV. (c) D600 was found to reduce the gating current in a voltage- and use-dependent manner. D600 was also found to induce "extra" charge movement at negative potentials. (d) Nitrendipine reduced the gating current in a voltage-dependent manner (KD = 200 nM at -40 mV). However, nitrendipine did not increase charge movement at negative test potentials. Although contamination of the Ca channel gating current from other sources cannot be fully excluded, it was not evident in the data and would appear to be small. However, it was noted that the amount of Ca channel gating charge was quite large compared with the magnitude of the Ca current. Indeed, the gating current was found to be a significant contaminant (19 +/- 7%) of the Ca tail currents in these cells. In addition, it was found that Ca channel rundown did not diminish the gating current. These results suggest that Ca channels can be "inactivated" by means that do not affect the voltage sensor.

Voltage-dependent calcium current and the effects of adrenergic modulation in rat aortic smooth muscle cells

1992 ◽  
Vol 337 (1279) ◽  
pp. 37-47 ◽  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Ca Channel ◽  
Ca Current ◽  
Inward Current ◽  
Aortic Smooth Muscle Cells ◽  
Aortic Smooth Muscle ◽  
Inward Currents ◽  
Sustained Inward Current

Smooth muscle cells from rat aorta were cultured in defined, serum-free medium and studied using whole-cell patch-clamp techniques. Under conditions designed to isolate currents through Ca channels, step depolarizations produced inward currents which were fast in onset and inactivated rapidly, with little sustained inward current being observed. Both Ni and Cd blocked these currents, with Ni being effective at 50 μM. Removal of external Na or addition of 1 μM tetrodotoxin had no effect. Peak inward currents were attained at about —15 mV, with half-maximal activation at —41 mV using —80 mV holding potentials. The transient inward currents were reduced by depolarized holding potentials, with half-maximal steady-state inactivation at —48 mV. In three of the 98 cells studied, small maintained inward currents were observed with a —40 mV holding potential. The Ca channel antagonist nicardipine (5 μM ) blocked the transient inward current while neither of the dihydropyridine Ca channel agonists S( + )202 791 and ( — )BAY K 8644 produced a significant augmentation of sustained inward current. At 10 μM, both noradrenaline and adrenaline but not phenylephrine decreased the peak inward current. This inhibition was unaffected by a variety of adrenoceptor antagonists and was also observed when internal solutions having high Ca buffering capacity were used, but was absent when GDP-β-S instead of GTP was included in the pipette solution. The main conclusions from this study are that under our cell culture conditions, rat aortic smooth muscle cells possess predominately a transient, low-threshold-activated inward Ca current and that this Ca current is inhibited by certain adrenoceptor agonists but with a quite atypical adrenoceptor antagonist pharmacology.

A mathematical model of phase 2 reentry: role of L-type Ca current

2003 ◽  
Vol 284 (4) ◽  
pp. H1285-H1294 ◽  
Author(s):  
Shunichiro Miyoshi ◽  
Hideo Mitamura ◽  
Kana Fujikura ◽  
Yukiko Fukuda ◽  
Kojiro Tanimoto ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Brugada Syndrome ◽  
Field Potential ◽  
Outward Current ◽  
Transient Outward Current ◽  
Ca Channel ◽  
Phase 2 ◽  
Ca Current ◽  
St Segment Elevation ◽  
St Segment

Phase 2 reentry (P2R) is known to be one of the mechanisms of malignant ventricular arrhythmias, especially those associated with Brugada syndrome. However, little is known about the underlying mechanism for P2R. Our aim in this study was to simulate P2R in a mathematical model to enable us to understand its mechanism and identify a potential therapeutic target. A mathematical model of the L-type Ca current was composed according to whole cell current data from guinea pig ventricular myocytes recorded at 37°C. Our mathematical model was incorporated into the modified Luo-Rudy phase 2 model. We set a dispersion in transient outward current ( I to) density within the theoretical fiber, composed of 80 serially arranged epicardial cells with gap junctions and then observed the P2R. The dispersion in I todensity within an only 0.8-cm epicardial theoretical fiber generated P2R with our Ca channel but not with the original model. When the P2R developed in the theoretical fiber, the calculated extracellular field potential showed coved-type ST segment elevation. We succeeded in generating P2R in our model for the first time. The local epicardial P2R may contribute the genesis of coved-type ST segment elevation in the Brugada syndrome.

A binding-site model for calcium channel inactivation that depends on calcium entry

1982 ◽  
Vol 217 (1206) ◽  
pp. 101-110 ◽  
Keyword(s):  
Membrane Surface ◽  
Calcium Entry ◽  
Ca Channel ◽  
Ca Channels ◽  
Ca Current ◽  
Two Phase ◽  
Site Model ◽  
Channel Inactivation ◽  
Calcium Channel Inactivation ◽  
Simplifying Assumptions

We describe a model for the mechanism by which Ca channel inactivation might depend on calcium entry. Ca is assumed to bind to a site at the internal membrane surface to cause inactivation of Ca channels. We assume that Ca that enters through the membrane accumulates in a submembrane compartment and also make simplifying assumptions about Ca buffering and removal. Our model predicts the results of single and double-pulse voltage-clamp experiments well. The predicted turn-off of Ca current is non-exponential. The model also predicts that procedures that slow inactivation will increase peak Ca current and suggests that both two-phase turn-off of currents and failure of normalized current to recover to 1. 0 in two-pulse experiments may be explained without assuming a voltage-dependent component of inactivation or two popu­lations of Ca channels.

scholarly journals Expression and roles of N-type Ca channel in cardiaomyocytes

2021 ◽  
Vol 42 (Supplement_1) ◽  
Author(s):  
M Kobara ◽  
H Toba ◽  
T Nakata
Keyword(s):  
Myocardial Infarction ◽  
Heart Failure ◽  
Cardiac Myocytes ◽  
Caspase 3 ◽  
Cardiac Tissue ◽  
Pathological Condition ◽  
Ca Channel ◽  
Myocyte Apoptosis ◽  
Ldh Release ◽  
Cultured Cardiomyocytes

Abstract Background Voltage dependent Ca channels are divided to L-, T-, N-, P/Q-, and R-types, and N-type Ca channel (NCC) is mainly expressed in nerve terminal and regulates neurotransmitter release. Recently, NCC has been reported to express in adrenal gland and renal tubular cells. We examined whether NCC is expressed in cardiac myocytes and if so, the roles of this channel. Methods Expression of NCC mRNA and protein in cardiomyocytes were assessed by quantitative real time PCR and Western blot analysis using neonatal rat cultured cardiomyocytes, infant, and adult rat hearts. Expression site of NCC in cardiomyocytes was examined by confocal imaging of immunofluorescent staining. The roles of NCC in physiological Ca transient in neonatal myocytes were examined using fluorescence imaging of Fluo4, an intracellular Ca indicator. To examine the effects of pathological condition, such as heart failure and ischemia-reperfusion, on NCC expression, cultured cardiomyocytes were treated with norepinephrine (10 μmol/L, 24 hours) or subjected to 5 hours of hypoxia followed by 30 minutes of reoxygenation. In addition, adult rats were subjected to myocardial infarction by ligating the left anterior coronary artery. Lethal myocyte injury was examined by LDH activity in culture medium and myocyte apoptosis was examined by nuclear staining with DAPI and caspase 3 activity. To clarify the roles of NCC in neonatal myocytes in these pathological conditions, we examine the effect of ω-conotoxin, a selective NCC blocker. Results NCC mRNA and protein were expressed in neonatal cardiomyocytes. Immunocytochemical staining showed NCC was expressed in myocyte plasma membrane. During physiological spontaneous beating, ω-conotoxin did not affect beating rate and intra cellular Ca transient, suggesting that the roles of NCC on physiological beating are little. After birth level of NCC mRNA expression in cardiac tissue gradually decreased within 2 weeks and low level of mRNA expressed continuously in adult cardiac tissue. However, in pathological condition, mRNA and protein levels of NCC in non-infarcted region were increased 4 weeks after myocardial infarction. In addition, hypoxia-reoxygenation and norepinephrine administration increased LDH release and myocyte apoptosis in association with increase in NCC expression in neonatal cultured myocytes. ω-conotoxin significantly suppressed hypoxia/reoxygenation- and norepinephrine-induced LDH release and caspase 3 activation. Conclusion NCC is expressed in neonatal cardiac myocytes and the expression level was decreased after birth. Pathological condition, such as ischemic heart disease and heart failure, upregulated NCC expression in cardiomyocytes and NCC exacerbated lethal myocyte injury, while roles of NCC in physiological beating are little. FUNDunding Acknowledgement Type of funding sources: None.

BAY K 8644 depresses excitation-contraction coupling in cardiac muscle

1996 ◽  
Vol 270 (3) ◽  
pp. C878-C884 ◽  
Author(s):  
E. McCall ◽  
D. M. Bers
Keyword(s):  
Cardiac Tissue ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Bay K 8644 ◽  
Ca Channel ◽  
Ca Current ◽  
Release Channel ◽  
Dihydropyridine Receptors ◽  
Current Voltage ◽  
The Relationship

We determined the effect of the dihydropyridine L-type Ca channel agonist BAY K 8644 (BAY) on excitation-contraction (E-C) coupling in isolated ferret ventricular myocytes using whole cell voltage clamp. The sarcoplasmic reticulum (SR) Ca load during the test pulses, assessed by caffeine-induced contractures, was similar in the presence and absence of BAY, with extracellular Ca concentration lowered from 3 to 1 mM in BAY. The relationship between L-type Ca current (ICa) and contraction was assessed, with current and contractions measured during depolarizations from -40 to between -30 and +50 mV after a conditioning train (to ensure constant SR Ca load). BAY shifted the current-contraction relationship downward, such that, for a given ICa and SR Ca load, the contraction elicited was much smaller in the presence of BAY. BAY also induced a characteristic negative shift in the the current-voltage relationship. We conclude that BAY decreases the efficacy of a given Ca current to induce SR Ca release during E-C coupling in ferret cardiac tissue (in contrast to the BAY-induced increase of resting SR Ca release). This may reflect an alteration in the state of the SR Ca release channel due to BAY binding to dihydropyridine receptors.

Measurement and simulation of noninactivating Ca current in smooth muscle cells

1989 ◽  
Vol 256 (4) ◽  
pp. C880-C885 ◽  
Author(s):  
Y. Imaizumi ◽  
K. Muraki ◽  
M. Takeda ◽  
M. Watanabe
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Ca Channel ◽  
Ca Current ◽  
Dependent Inactivation ◽  
High K ◽  
Voltage Dependent ◽  
Rabbit Portal Vein

An attempt was made to obtain electrophysiological evidence for continuous influx of Ca ion through voltage-dependent Ca channel (VDCC) in smooth muscle during long depolarization, for example in high K solution. Noninactivated Ca current [ICa(ni)] remaining after the accomplishment of voltage-dependent inactivation by prolonged depolarization for approximately 1 min was detected by three means under whole cell voltage clamp in several types of smooth muscle cells. The measurement of ICa(ni) was performed by micropuff application of Cd2+ or Ca2+ in the presence or absence of 5 mM extracellular Ca, respectively, or jump of extracellular Ca concentration [( Ca]o). The current-voltage relationship of ICa(ni) evaluated by these means had a peak at approximately -10 mV. The peak amplitude ranged from 5 to 25 pA, depending on whether the cells were isolated from guinea pig urinary bladder, ureter, vas deferens, taenia caecum, or rabbit portal vein. The ICa(ni) may be large enough to explain sustained contraction in high K solution, at least in these smooth muscle tissues. A window current simulated from the steady-state activation and inactivation curves and the maximum conductance of Ca current (ICa) in these cells suggests a theoretical basis for the observed ICa(ni).

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