scholarly journals Lipopolysaccharide prolongs action potential duration in HL-1 mouse cardiomyocytes

2012 ◽  
Vol 303 (8) ◽  
pp. C825-C833 ◽  
Author(s):  
Robert Wondergem ◽  
Bridget M. Graves ◽  
Chuanfu Li ◽  
David L. Williams
Keyword(s):  
Action Potential ◽  
Action Potential Duration ◽  
Salmonella Enteritidis ◽  
Time Course ◽  
Outward Current ◽  
Cell Voltage ◽  
Delayed Rectifier ◽  
Maximal Effect ◽  
Cellular Mechanisms ◽  
Whole Cell

Sepsis has deleterious effects on cardiac function including reduced contractility. We have shown previously that lipopolysaccharides (LPS) directly affect HL-1 cardiac myocytes by inhibiting Ca2+ regulation and by impairing pacemaker “funny” current, If. We now explore further cellular mechanisms whereby LPS inhibits excitability in HL-1 cells. LPS (1 μg/ml) derived from Salmonella enteritidis decreased rate of firing of spontaneous action potentials in HL-1 cells, and it increased their pacemaker potential durations and decreased their rates of depolarization, all measured by whole cell current clamp. LPS also increased action potential durations and decreased their amplitude in cells paced at 1 Hz with 0.1 nA, and 20 min were necessary for maximal effect. LPS decreased the amplitude of a rapidly inactivating inward current attributed to Na+ and of an outward current attributed to K+; both were measured by whole cell voltage clamp. The K+ currents displayed a resurgent outward tail current, which is characteristic of the rapid delayed-rectifier K+ current, IKr. LPS accordingly reduced outward currents measured with pipette Cs+ substituted for K+ to isolate IKr. E-4031 (1 μM) markedly inhibited IKr in HL-1 cells and also increased action potential duration; however, the direct effects of E-4031 occurred minutes faster than the slow effects of LPS. We conclude that LPS increases action potential duration in HL-1 mouse cardiomyocytes by inhibition of IKr and decreases their rate of firing by inhibition of INa. This protracted time course points toward an intermediary metabolic event, which either decreases available mouse ether-a-go-go (mERG) and Na+ channels or potentiates their inactivation.

Developmental Regulation of Whole Cell Capacitance and Membrane Current in Identified Interneurons in C. elegans

2006 ◽  
Vol 95 (6) ◽  
pp. 3665-3673 ◽  
Author(s):  
Serge Faumont ◽  
Thomas Boulin ◽  
Oliver Hobert ◽  
Shawn R. Lockery
Keyword(s):  
Time Course ◽  
Homeobox Gene ◽  
Outward Current ◽  
Cell Voltage ◽  
Membrane Current ◽  
Immunoglobulin Superfamily ◽  
Loss Of Function ◽  
Whole Cell ◽  
Steady State Current ◽  
Cell Capacitance

Postembryonic developmental changes in electrophysiological properties of the AIY interneuron class were investigated using whole cell voltage clamp. AIY interneurons displayed an increase in cell capacitance during larval development, whereas steady-state current amplitude did not increase. The time course of the outward membrane current, carried at least in part by K+ ions, matured, from a slowly activating, sustained current to a rapidly activating, decaying current. We also investigated how the development of capacitance and outward current was altered by loss-of-function mutations in genes expressed in AIY. One such gene, the LIM homeobox gene ttx-3, is known to be involved in the specification of the AIY neuronal subtype. In ttx-3 mutants, capacitance and outward current matured precociously. In mutants of the gene wrk-1, an immunoglobulin superfamily (IgSF) member whose expression is regulated by ttx-3, capacitance matured normally, whereas outward current matured precociously. We conclude that AIY interneurons contain distinct pathways for regulating capacitance and membrane current.

Effects of myocardial hypertrophy on transient outward current

1994 ◽  
Vol 266 (5) ◽  
pp. H1738-H1745 ◽  
Author(s):  
Q. Li ◽  
E. C. Keung
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Action Potential Duration ◽  
Time Course ◽  
Myocardial Hypertrophy ◽  
Pressure Overload ◽  
Reversal Potential ◽  
Outward Current ◽  
Transient Outward Current ◽  
The Difference

In the one-clip, two-kidney model of hypertensive rat, a gradual chronic pressure overload is imposed on the heart. Myocardial hypertrophy resulting from such pressure overload is associated with an increased but slower inactivating L-type calcium current and prolongation of action potential duration. Voltage clamp experiments in a variety of excitable tissues indicate that a 4-aminopyridine-sensitive transient outward current (Ito) plays an important role in regulating the action potential duration. Accordingly, we studied Ito in single adult cardiac myocytes enzymatically isolated from hypertrophied left ventricles of the renovascular hypertensive (HBP) rat hearts using the whole cell patch-clamp method. The current densities (normalized to cell capacitative surface area) measured at the early transient peak Ito, at the steady state, and as the difference between the transient peak and the steady state were larger in HBP cells (n = 23) than in control (Ctrl) cells (n = 20) (P < 0.05). There was no difference in the Ito reversal potential between Ctrl (-60.9 +/- 1.9 mV, mean +/- SE; n = 16) and HBP (-63.7 +/- 2.6 mV; n = 19) cells. The observed increase in Ito amplitude was not due to an increase in the number of channels available for activation or in the fraction of channels activated because there were no statistical differences in the membrane potential at which one-half of the Ito channels are activated (V0.5) for the steady-state activation and inactivation curves between Ctrl and HBP cells. The time course of inactivation of Ito was described by a double-exponential function.(ABSTRACT TRUNCATED AT 250 WORDS)

A- and C-type rat nodose sensory neurons: model interpretations of dynamic discharge characteristics

1994 ◽  
Vol 71 (6) ◽  
pp. 2338-2358 ◽  
Author(s):  
J. H. Schild ◽  
J. W. Clark ◽  
M. Hay ◽  
D. Mendelowitz ◽  
M. C. Andresen ◽  
...  
Keyword(s):  
Action Potential ◽  
Sensory Neurons ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Current Clamp ◽  
Patch Clamp Technique ◽  
Whole Cell ◽  
Response Properties ◽  
Wide Range

1. Neurons of the nodose ganglia provide the sole connection between many types of visceral sensory inputs and the central nervous system. Electrophysiological studies of isolated nodose neurons provide a practical means of measuring individual cell membrane currents and assessing their putative contributions to the overall response properties of the neuron and its terminations. Here, we present a comprehensive mathematical model of an isolated nodose sensory neuron that is based upon numerical fits to quantitative voltage- and current-clamp data recorded in our laboratory. Model development was accomplished using an iterative process of electrophysiological recordings, nonlinear parameter estimation, and computer simulation. This work is part of an integrative effort aimed at identifying and characterizing the fundamental ionic mechanisms participating in the afferent neuronal limb of the baroreceptor reflex. 2. The neuronal model consists of two parts: a Hodgkin-Huxley-type membrane model coupled to a lumped fluid compartment model that describes Ca2+ ion concentration dynamics within the intracellular and external perineuronal media. Calcium buffering via a calmodulin-type buffer is provided within the intracellular compartment. 3. The complete model accurately reproduces whole-cell voltage-clamp recordings of the major ion channel currents observed in enzymatically dispersed nodose sensory neurons. Specifically, two Na+ currents exhibiting fast (INaf) and slow tetrodotoxin (TTX)-insensitive (INas) kinetics; low- and high-threshold Ca2+ currents exhibiting transient (ICa,t) and long-lasting (ICa,n) dynamics, respectively; and outward K+ currents consisting of a delayed-rectifier current (IK), a transient outward current (I(t)) and a Ca(2+)-activated K+ current (IK,Ca). 4. Whole-cell current-clamp recordings of somatic action-potential dynamics were performed on enzymatically dispersed nodose neurons using the perforated patch-clamp technique. Stimulus protocols consisted of both short (< or = 2.0 ms) and long (> or = 200 ms) duration current pulses over a wide range of membrane holding potentials. These studies clearly revealed two populations of nodose neurons, often termed A- and C-type cells, which exhibit markedly different action-potential signatures and stimulus response properties. 5. Using a single set of equations, the model accurately reproduces the electrical behavior of both A- and C-type nodose neurons in response to a wide variety of stimulus conditions and membrane holding potentials. The structure of the model, as well as the majority of its parameters are the same for both A- and C-type implementations.(ABSTRACT TRUNCATED AT 400 WORDS)

Whole-cell recording of light-evoked photoreceptor responses in a slice preparation of the cuttlefish retina

2005 ◽  
Vol 22 (3) ◽  
pp. 359-370 ◽  
Author(s):  
ABDESSLAM CHRACHRI ◽  
LISA NELSON ◽  
RODDY WILLIAMSON
Keyword(s):  
Time Course ◽  
Early Stage ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
Slice Preparation ◽  
Whole Cell ◽  
Inward Current ◽  
Transient Inward Current ◽  
Dose Dependent

A new tissue slice preparation of the cuttlefish eye is described that permits patch-clamp recordings to be acquired from intact photoreceptors during stimulation of the retina with controlled light flashes. Whole-cell recordings using this preparation, from the retinas of very youngSepia officinalisdemonstrated that the magnitude, latency, and kinetics of the flash-induced photocurrent are closely dependent on the magnitude of the flash intensity. Depolarizing steps to voltages more positive than −40 mV, from a membrane holding potential of −60 mV, induced a transient inward current followed by a larger, more sustained outward current in these early-stage photoreceptors. The latter current resembled the delayed rectifier (IK) already identified in many other nerve cells, including photoreceptors. This current was activated at −30 mV from a holding potential of −60 mV, had a sustained time course, and was blocked in a dose-dependent manner by tetraethylammonium chloride (TEA). The smaller, transient, inward current appeared at potentials more positive than −50 mV, reached peak amplitude at −30 mV and decreased with further depolarization. This current was characterized as the sodium current (INa) on the basis that it was inactivated at holding potentials above −40 mV, was blocked by tetrodotoxin (TTX) and was insensitive to cobalt.Intracellular perfusion of the photoreceptors,viathe patch pipette, demonstrated that U-73122 and heparin blocked the evoked photocurrent in a dose-dependent manner, suggesting the involvement of the phospholipase C (PLC) and inositol 1,4,5-triphosphate (InsP3), respectively, in the phototransduction cascade. Perfusion with cyclic GMP increased significantly the evoked photocurrent, while the inclusion of phorbol-12,13-dibutyrate reduced significantly the evoked photocurrent, supporting the involvement of cGMP and the diacylglycerol (DAG) pathways, respectively, in the cuttlefish transduction process.

Decreased transient outward K+ current in ventricular myocytes from acromegalic rats

1991 ◽  
Vol 260 (3) ◽  
pp. H935-H942 ◽  
Author(s):  
X. P. Xu ◽  
P. M. Best
Keyword(s):  
Action Potential ◽  
Action Potential Duration ◽  
Time Course ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Resting Potential ◽  
Gh3 Cells ◽  
Heart Weight ◽  
Transient Outward Current ◽  
Tumor Bearing

Cardiac hypertrophy and heart failure are common to acromegalic patients who have abnormally high serum growth hormone (GH). While the function of cardiac muscle is clearly affected by chronically elevated GH, the electrical activity of myocytes from hearts with GH-dependent hypertrophy has not been studied. We used adult, female Wistar-Furth rats with induced GH-secreting tumors to study the effect of excessive GH on ion channels of cardiac myocytes. GH-secreting tumors were induced by subcutaneous inoculation of GH3 cells. Eight weeks after inoculation, the rats had doubled their body weight and heart size compared with age-matched controls. There were no differences in either action potential amplitude or resting potential of right ventricular myocytes from control and tumor-bearing rats. However, action potential duration increased significantly in tumor-bearing rats; the time to 50% repolarization was 23 +/- 14 ms (n = 10) compared with 6.6 +/- 1.5 ms (n = 14) in controls. The prolongation of the action potential was mainly due to a decrease in density of a transient outward current (It,o) carried by K+. The normalized conductance for It,o decreased from 0.53 +/- 0.10 nS/pF (n = 25) in controls to 0.33 +/- 0.09 nS/pF (n = 26) in tumor-bearing rats. The decrease in It,o) and increase in heart weight occurred with a similar time course. The increased action potential duration prolongs Ca2+ influx through L-type Ca2+ channels in the tumor-bearing animals; this may be important in cardiovascular adaptation.

K+ currents in rabbit esophageal muscularis mucosae

1993 ◽  
Vol 264 (5) ◽  
pp. G1001-G1007 ◽  
Author(s):  
H. I. Akbarali
Keyword(s):  
Single Cells ◽  
Outward Current ◽  
Cell Voltage ◽  
Resting Potential ◽  
Delayed Rectifier ◽  
Muscularis Mucosae ◽  
Whole Cell ◽  
Electrophysiological Properties ◽  
Perforated Patch ◽  
K Current

Single cells were obtained from esophageal muscularis mucosae of the rabbit using enzymatic dispersion. Their electrophysiological properties were studied with both conventional whole cell and nystatin-perforated patch techniques. The latter technique was used to prevent "washout" of intracellular constituents and to maintain endogenous buffering of Ca2+. The average resting potential of these cells was -54 +/- 3.2 mV in the conventional recording and -51 +/- 4.4 mV in perforated patch recordings. In the current-clamp mode, regenerative responses were consistently observed in perforated patch recordings, but not when conventional whole cell gigaseal methods were used. Conventional whole cell voltage-clamp methods revealed outward currents on depolarization from a holding potential of -70 mV. These currents were inhibited by extracellular tetraethylammonium (TEA, 5-10 mM) and CoCl2 (4 mM), indicating that the predominant outward current is a Ca(2+)-activated K+ current. In the presence of TEA, inward Ca2+ currents were unmasked. In contrast, when the nystatin-perforated patch technique was used, depolarizations resulted in a net inward current followed by an outward current. The outward current was inhibited by CoCl2 (2 mM) and TEA (5 mM) to the same extent as in conventional recordings. A second component of K+ current was observed in both types of recordings when extracellular Ca2+ influx was abolished and also in the presence of TEA. This slowly activating persistent K+ current resembled a delayed rectifier K+ current. These studies show that the rabbit tunica muscularis mucosal cells possess voltage-activated Ca2+ and K+ channels as well as the capability to elicit action potentials.

scholarly journals Inactivation of A currents and A channels on rat nodose neurons in culture.

1989 ◽  
Vol 94 (5) ◽  
pp. 881-910 ◽  
Author(s):  
E Cooper ◽  
A Shrier
Keyword(s):  
Time Course ◽  
Single Channel ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Whole Cell ◽  
Relative Contribution ◽  
Delayed Rectifier Current ◽  
Nodose Ganglia ◽  
Open Time ◽  
A Current

Cultured sensory neurons from nodose ganglia were investigated with whole-cell patch-clamp techniques and single-channel recordings to characterize the A current. Membrane depolarization from -40 mV holding potential activated the delayed rectifier current (IK) at potentials positive to -30 mV; this current had a sigmoidal time course and showed little or no inactivation. In most neurons, the A current was completely inactivated at the -40 mV holding potential and required hyperpolarization to remove the inactivation; the A current was isolated by subtracting the IK evoked by depolarizations from -40 mV from the total outward current evoked by depolarizations from -90 mV. The decay of the A current on several neurons had complex kinetics and was fit by the sum of three exponentials whose time constants were 10-40 ms, 100-350 ms, and 1-3 s. At the single-channel level we found that one class of channel underlies the A current. The conductance of A channels varied with the square root of the external K concentration: it was 22 pS when exposed to 5.4 mM K externally, the increased to 40 pS when exposed to 140 mM K externally. A channels activated rapidly upon depolarization and the latency to first opening decreased with depolarization. The open time distributions followed a single exponential and the mean open time increased with depolarization. A channels inactivate in three different modes: some A channels inactivated with little reopening and gave rise to ensemble averages that decayed in 10-40 ms; other A channels opened and closed three to four times before inactivating and gave rise to ensemble averages that decayed in 100-350 ms; still other A channels opened and closed several hundred times and required seconds to inactivate. Channels gating in all three modes contributed to the macroscopic A current from the whole cell, but their relative contribution differed among neurons. In addition, A channels could go directly from the closed, or resting, state to the inactivated state without opening, and the probability for channels inactivating in this way was greater at less depolarized voltages. In addition, a few A channels appeared to go reversibly from a mode where inactivation occurred rapidly to a slow mode of inactivation.

scholarly journals Canine Myocytes Represent a Good Model for Human Ventricular Cells Regarding Their Electrophysiological Properties

2021 ◽  
Vol 14 (8) ◽  
pp. 748
Author(s):  
Péter P. Nánási ◽  
Balázs Horváth ◽  
Fábián Tar ◽  
János Almássy ◽  
Norbert Szentandrássy ◽  
...  
Keyword(s):  
Action Potential ◽  
Time Course ◽  
Laboratory Animals ◽  
Delayed Rectifier ◽  
Ion Currents ◽  
Human Cardiomyocytes ◽  
Ventricular Cells ◽  
Repolarization Reserve ◽  
Electrophysiological Studies ◽  
K Current

Due to the limited availability of healthy human ventricular tissues, the most suitable animal model has to be applied for electrophysiological and pharmacological studies. This can be best identified by studying the properties of ion currents shaping the action potential in the frequently used laboratory animals, such as dogs, rabbits, guinea pigs, or rats, and comparing them to those of human cardiomyocytes. The authors of this article with the experience of three decades of electrophysiological studies, performed in mammalian and human ventricular tissues and isolated cardiomyocytes, summarize their results obtained regarding the major canine and human cardiac ion currents. Accordingly, L-type Ca2+ current (ICa), late Na+ current (INa-late), rapid and slow components of the delayed rectifier K+ current (IKr and IKs, respectively), inward rectifier K+ current (IK1), transient outward K+ current (Ito1), and Na+/Ca2+ exchange current (INCX) were characterized and compared. Importantly, many of these measurements were performed using the action potential voltage clamp technique allowing for visualization of the actual current profiles flowing during the ventricular action potential. Densities and shapes of these ion currents, as well as the action potential configuration, were similar in human and canine ventricular cells, except for the density of IK1 and the recovery kinetics of Ito. IK1 displayed a largely four-fold larger density in canine than human myocytes, and Ito recovery from inactivation displayed a somewhat different time course in the two species. On the basis of these results, it is concluded that canine ventricular cells represent a reasonably good model for human myocytes for electrophysiological studies, however, it must be borne in mind that due to their stronger IK1, the repolarization reserve is more pronounced in canine cells, and moderate differences in the frequency-dependent repolarization patterns can also be anticipated.

Dual effects of external magnesium on action potential duration in guinea pig ventricular myocytes

1995 ◽  
Vol 268 (6) ◽  
pp. H2321-H2328 ◽  
Author(s):  
S. Zhang ◽  
T. Sawanobori ◽  
H. Adaniya ◽  
Y. Hirano ◽  
M. Hiraoka
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Decay Time ◽  
Action Potential Duration ◽  
Time Course ◽  
Ventricular Myocytes ◽  
Membrane Surface ◽  
Surface Charges ◽  
Whole Cell Patch Clamp ◽  
K Current

Effects of extracellular magnesium (Mg2+) on action potential duration (APD) and underlying membrane currents in guinea pig ventricular myocytes were studied by using the whole cell patch-clamp method. Increasing external Mg2+ concentration [Mg2+]o) from 0.5 to 3 mM produced a prolongation of APD at 90% repolarization (APD90), whereas 5 and 10 mM Mg2+ shortened it. [Mg2+]o, at 3 mM or higher, suppressed the delayed outward K+ current and the inward rectifier K+ current. Increases in [Mg2+]o depressed the peak amplitude and delayed the decay time course of the Ca2+ current (ICa), the latter effect is probably due to the decrease in Ca(2+)-induced inactivation. Thus 3 mM Mg2+ suppressed the peak ICa but increased the late ICa amplitude at the end of a 200-ms depolarization pulse, whereas 10 mM Mg2+ suppressed both components. Application of 10 mM Mg2+ shifted the voltage-dependent activation and inactivation by approximately 10 mV to more positive voltage due to screening the membrane surface charges. Application of manganese (1-5 mM) also caused dual effects on APD90, similar to those of Mg2+, and suppressed the peak ICa with slowed decay. These results suggest that the dual effects of Mg2+ on APD in guinea pig ventricular myocytes can be, at least in part, explained by its action on ICa with slowed decay time course in addition to suppressive effects on K+ currents.

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