L-type but not T-type calcium current changes during postnatal development in rabbit sinoatrial node

2001 ◽  
Vol 281 (3) ◽  
pp. H1252-H1259 ◽  
Author(s):  
Lev Protas ◽  
Dario DiFrancesco ◽  
Richard B. Robinson
Keyword(s):  
Calcium Current ◽  
Sinoatrial Node ◽  
Voltage Dependence ◽  
Sodium Current ◽  
Sinus Node ◽  
Calcium Currents ◽  
Potential Contribution ◽  
Patch Clamps ◽  
Diastolic Depolarization ◽  
Rabbit Sinoatrial Node

Although the neonatal sinus node beats at a faster rate than the adult, when a sodium current ( I Na) present in the newborn is blocked, the spontaneous rate is slower in neonatal myocytes than in adult myocytes. This suggests a possible functional substitution of I Na by another current during development. We used ruptured [T-type calcium current ( I Ca,T)] and perforated [L-type calcium current ( I Ca,L)] patch clamps to study developmental changes in calcium currents in sinus node cells from adult and newborn rabbits. I Ca,T density did not differ with age, and no significant differences were found in the voltage dependence of activation or inactivation. I Ca,L density was lower in the adult than newborn (12.1 ± 1.4 vs. 17.6 ± 2.5 pA/pF, P = 0.049). However, activation and inactivation midpoints were shifted in opposite directions, reducing the potential contribution during late diastolic depolarization in the newborn (activation midpoints −17.3 ± 0.8 and −22.3 ± 1.4 mV in the newborn and adult, respectively, P = 0.001; inactivation midpoints −33.4 ± 1.4 and −28.3 ± 1.7 mV for the newborn and adult, respectively, P = 0.038). Recovery of I Ca,L from inactivation was also slower in the newborn. The results suggest that a smaller but more negatively activating and rapidly recovering I Ca,L in the adult sinus node may contribute to the enhanced impulse initiation at this age in the absence of I Na.

scholarly journals Effect of FMRFamide on voltage-dependent currents in identified centrifugal neurons of the optic lobe of the cuttlefish, Sepia officinalis

2020 ◽  
Author(s):  
Abdesslam Chrachri
Keyword(s):  
Visual Processing ◽  
Calcium Current ◽  
Optic Lobe ◽  
Low Voltage ◽  
Sodium Current ◽  
Calcium Currents ◽  
Delayed Rectifier ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents

AbstractWhole-cell patch-clamp recordings from identified centrifugal neurons of the optic lobe in a slice preparation allowed the characterization of five voltage-dependent currents; two outward and three inward currents. The outward currents were; the 4-aminopyridine-sensitive transient potassium or A-current (IA), the TEA-sensitive sustained current or delayed rectifier (IK). The inward currents were; the tetrodotoxin-sensitive transient current or sodium current (INa). The second is the cobalt- and cadmium-sensitive sustained current which is enhanced by barium and blocked by the dihydropyridine antagonist, nifedipine suggesting that it could be the L-type calcium current (ICaL). Finally, another transient inward current, also carried by calcium, but unlike the L-type, this current is activated at more negative potentials and resembles the low-voltage-activated or T-type calcium current (ICaT) of other preparations.Application of the neuropeptide FMRFamide caused a significant attenuation to the peak amplitude of both sodium and sustained calcium currents without any apparent effect on the transient calcium current. Furthermore, FMRFamide also caused a reduction of both outward currents in these centrifugal neurons. The fact that FMRFamide reduced the magnitude of four of five characterized currents could suggest that this neuropeptide may act as a strong inhibitory agent on these neurons.SummaryFMRFamide modulate the ionic currents in identified centrifugal neurons in the optic lobe of cuttlefish: thus, FMRFamide could play a key role in visual processing of these animals.

scholarly journals Contribution of L-type Ca2+current to electrical activity in sinoatrial nodal myocytes of rabbits

1999 ◽  
Vol 276 (3) ◽  
pp. H1064-H1077 ◽  
Author(s):  
E. Etienne Verheijck ◽  
Antoni C. G. van Ginneken ◽  
Ronald Wilders ◽  
Lennart N. Bouman
Keyword(s):  
Action Potential ◽  
Calcium Current ◽  
Sodium Current ◽  
Delayed Rectifier ◽  
Current Clamp ◽  
Patch Clamp Technique ◽  
Inward Current ◽  
Delayed Rectifier Current ◽  
Diastolic Depolarization ◽  
Recovery From Inactivation

The role of L-type calcium current ( I Ca,L) in impulse generation was studied in single sinoatrial nodal myocytes of the rabbit, with the use of the amphotericin-perforated patch-clamp technique. Nifedipine, at a concentration of 5 μM, was used to block I Ca,L. At this concentration, nifedipine selectively blocked I Ca,L for 81% without affecting the T-type calcium current ( I Ca,T), the fast sodium current, the delayed rectifier current ( I K), and the hyperpolarization-activated inward current. Furthermore, we did not observe the sustained inward current. The selective action of nifedipine on I Ca,L enabled us to determine the activation threshold of I Ca,L, which was around −60 mV. As nifedipine (5 μM) abolished spontaneous activity, we used a combined voltage- and current-clamp protocol to study the effects of I Ca,L blockade on repolarization and diastolic depolarization. This protocol mimics the action potential such that the repolarization and subsequent diastolic depolarization are studied in current-clamp conditions. Nifedipine significantly decreased action potential duration at 50% repolarization and reduced diastolic depolarization rate over the entire diastole. Evidence was found that recovery from inactivation of I Ca,L occurs during repolarization, which makes I Ca,L available already early in diastole. We conclude that I Ca,L contributes significantly to the net inward current during diastole and can modulate the entire diastolic depolarization.

scholarly journals Unique Ca2+-Cycling Protein Abundance and Regulation Sustains Local Ca2+ Releases and Spontaneous Firing of Rabbit Sinoatrial Node Cells

2018 ◽  
Vol 19 (8) ◽  
pp. 2173 ◽  
Author(s):  
Tatiana Vinogradova ◽  
Syevda Tagirova (Sirenko) ◽  
Edward Lakatta
Keyword(s):  
Sinoatrial Node ◽  
Ventricular Myocytes ◽  
Ryanodine Receptors ◽  
Cell Types ◽  
Protein Abundance ◽  
Gradual Change ◽  
Spontaneous Firing ◽  
Diastolic Depolarization ◽  
Sinoatrial Node Cells ◽  
Rabbit Sinoatrial Node

Spontaneous beating of the heart pacemaker, the sinoatrial node, is generated by sinoatrial node cells (SANC) and caused by gradual change of the membrane potential called diastolic depolarization (DD). Submembrane local Ca2+ releases (LCR) from sarcoplasmic reticulum (SR) occur during late DD and activate an inward Na+/Ca2+ exchange current, which accelerates the DD rate leading to earlier occurrence of an action potential. A comparison of intrinsic SR Ca2+ cycling revealed that, at similar physiological Ca2+ concentrations, LCRs are large and rhythmic in permeabilized SANC, but small and random in permeabilized ventricular myocytes (VM). Permeabilized SANC spontaneously released more Ca2+ from SR than VM, despite comparable SR Ca2+ content in both cell types. In this review we discuss specific patterns of expression and distribution of SR Ca2+ cycling proteins (SR Ca2+ ATPase (SERCA2), phospholamban (PLB) and ryanodine receptors (RyR)) in SANC and ventricular myocytes. We link ability of SANC to generate larger and rhythmic LCRs with increased abundance of SERCA2, reduced abundance of the SERCA inhibitor PLB. In addition, an increase in intracellular [Ca2+] increases phosphorylation of both PLB and RyR exclusively in SANC. The differences in SR Ca2+ cycling protein expression between SANC and VM provide insights into diverse regulation of intrinsic SR Ca2+ cycling that drives automaticity of SANC.

Removal of sialic acid alters both T- and L-type calcium currents in cardiac myocytes

1991 ◽  
Vol 260 (3) ◽  
pp. H735-H743 ◽  
Author(s):  
B. Fermini ◽  
R. D. Nathan
Keyword(s):  
Sialic Acid ◽  
Sinoatrial Node ◽  
Calcium Currents ◽  
Pacemaker Cells ◽  
Patch Clamp Technique ◽  
Inactivation Curve ◽  
Node Removal ◽  
Rabbit Sinoatrial Node ◽  
Ca2 Channels ◽  
In Cells

The whole cell configuration of the patch-clamp technique was used to test the hypothesis that the presence of sialic acid residues influences both T- and L-type Ca2+ currents (ICa,T and ICa,L) in cultured pacemaker cells isolated from the rabbit sinoatrial node. Removal of these anionic sugar moieties by neuraminidase (1.0 U/ml for 5-20 min) increased ICa,T in five of nine cells (by a factor of 2.2-5.1) and ICa,L in three of six cells (by a factor of 1.2-1.6). In cells that did not exhibit such an increase, the enzyme reduced ICa,T but had no significant effect on ICa,L. In cells that exhibited an increase in ICa,T, exposure to neuraminidase also shifted the activation curve to more negative potentials and increased the slope of the inactivation curve. The enzyme did not influence the gating of ICa,L or the rates of inactivation of either ICa,T or ICa,L. The enhancement of ICa,T and ICa,L could not be mimicked by including neuraminidase in the patch pipette or by adding a contaminant of the enzyme preparation, phospholipase C, to the bath. When external Ca2+ was replaced by Ba2+, neither ICa,T nor ICa,L was increased significantly by neuraminidase. It is proposed that by removing sialic acid residues neuraminidase might directly alter the gating of T-type Ca2+ channels. On the other hand, the increased amplitudes of ICa,T and ICa,L might be due to a rise in intracellular Ca2+.

Characterization of inward currents and channels underlying burst activity in motoneurons of crab cardiac ganglion

2013 ◽  
Vol 110 (1) ◽  
pp. 42-54 ◽  
Author(s):  
Joseph L. Ransdell ◽  
Simone Temporal ◽  
Nicole L. West ◽  
Megan L. Leyrer ◽  
David J. Schulz
Keyword(s):  
Calcium Channel ◽  
Calcium Current ◽  
Sodium Current ◽  
Large Cell ◽  
Calcium Currents ◽  
Cardiac Ganglion ◽  
Cancer Borealis ◽  
Cationic Current ◽  
Inward Currents

Large cell motoneurons in the Cancer borealis cardiac ganglion generate rhythmic bursts of action potentials responsible for cardiac contractions. While it is well known that these burst potentials are dependent on coordinated interactions among depolarizing and hyperpolarizing conductances, the depolarizing currents present in these cells, and their biophysical characteristics, have not been thoroughly described. In this study we used a combined molecular biology and electrophysiology approach to look at channel identity, expression, localization, and biophysical properties for two distinct high-voltage-activated calcium currents present in these cells: a slow calcium current ( ICaS) and a transient calcium current ( ICaT). Our data indicate that CbCaV1 is a putative voltage-gated calcium channel subunit in part responsible for an L-type current, while CbCaV2 (formerly cacophony) is a subunit in part responsible for a P/Q-type current. These channels appear to be localized primarily to the somata of the motoneurons. A third calcium channel gene (CbCaV3) was identified that encodes a putative T-type calcium channel subunit and is expressed in these cells, but electrophysiological studies failed to detect this current in motoneuron somata. In addition, we identify and characterize for the first time in these cells a calcium-activated nonselective cationic current ( ICAN), as well as a largely noninactivating TTX-sensitive current reminiscent of a persistent sodium current. The identification and further characterization of these currents allow both biological and modeling studies to move forward with more attention to the complexity of interactions among these distinct components underlying generation of bursting output in motoneurons.

Voltage-dependent calcium currents in rat gonadotropes separated by centrifugal elutriation

1990 ◽  
Vol 258 (4) ◽  
pp. E589-E596 ◽  
Author(s):  
C. Marchetti ◽  
G. V. Childs ◽  
A. M. Brown
Keyword(s):  
Time Constant ◽  
Calcium Current ◽  
Low Voltage ◽  
Sodium Current ◽  
Ionic Currents ◽  
Physiological Solution ◽  
Calcium Currents ◽  
Pituitary Cells ◽  
Centrifugal Elutriation ◽  
Rat Pituitary Cells

Centrifugal elutriation of rat pituitary cells yielded two functionally active fractions (6 and 7) that contained 30-40 and 50-60% gonadotropes, respectively. We studied the membrane ionic currents of these cells with the whole cell patch-clamp method. In physiological solution, cells from the enriched fractions displayed a tetrodotoxin-sensitive sodium current. In 20 mM external calcium and zero sodium, the inward current contained two components that were different in threshold, steady-state inactivation, and deactivation. One component was half activated at approximately -25 mV, half inactivated from a holding potential of -61 mV, and deactivated with a time constant of 3 ms. The second component was half activated at 6 mV and deactivated with a time constant of 0.35 ms. These two currents resembled the high-voltage-activated and low-voltage-activated calcium current described in many preparations, including clonal and primary pituitary cells. Bath application of 20 nM gonadotropin-releasing hormone caused a transient and reversible decrease of the calcium current at depolarized voltages and a negative shift of 10 mV in the activation curve. Both effects were observed in a percentage of cells that closely matches the percentage of gonadotropes in the fraction. The shift appeared to affect both components of the current and can partially account for the increased activity of Ca2+ channels at potentials close to the resting value.

scholarly journals Relationship of calcium transients to calcium currents and charge movements in myotubes expressing skeletal and cardiac dihydropyridine receptors.

1994 ◽  
Vol 103 (1) ◽  
pp. 125-147 ◽  
Author(s):  
J García ◽  
T Tanabe ◽  
K G Beam
Keyword(s):  
Skeletal Muscle ◽  
Calcium Channel ◽  
Calcium Current ◽  
Calcium Release ◽  
Voltage Dependence ◽  
Calcium Transient ◽  
Calcium Currents ◽  
Calcium Transients ◽  
Charge Movement ◽  
The Relationship

In both skeletal and cardiac muscle, the dihydropyridine (DHP) receptor is a critical element in excitation-contraction (e-c) coupling. However, the mechanism for calcium release is completely different in these muscles. In cardiac muscle the DHP receptor functions as a rapidly-activated calcium channel and the influx of calcium through this channel induces calcium release from the sarcoplasmic reticulum (SR). In contrast, in skeletal muscle the DHP receptor functions as a voltage sensor and as a slowly-activating calcium channel; in this case, the voltage sensor controls SR calcium release. It has been previously demonstrated that injection of dysgenic myotubes with cDNA (pCAC6) encoding the skeletal muscle DHP receptor restores the slow calcium current and skeletal type e-c coupling that does not require entry of external calcium (Tanabe, Beam, Powell, and Numa. 1988. Nature. 336:134-139). Furthermore, injection of cDNA (pCARD1) encoding the cardiac DHP receptor produces rapidly activating calcium current and cardiac type e-c coupling that does require calcium entry (Tanabe, Mikami, Numa, and Beam. 1990. Nature. 344:451-453). In this paper, we have studied the voltage dependence of, and the relationship between, charge movement, calcium transients, and calcium current in normal skeletal muscle cells in culture. In addition, we injected pCAC6 or pCARD1 into the nuclei of dysgenic myotubes and studied the relationship between the restored events and compared them with those of the normal cells. Charge movement and calcium currents were recorded with the whole cell patch-clamp technique. Calcium transients were measured with Fluo-3 introduced through the patch pipette. The kinetics and voltage dependence of the charge movement, calcium transients, and calcium current in dysgenic myotubes expressing pCAC6 were qualitatively similar to the ones elicited in normal myotubes: the calcium transient displayed a sigmoidal dependence on voltage and was still present after the addition of 0.5 mM Cd2+ + 0.1 mM La3+. In contrast, the calcium transient in dysgenic myotubes expressing pCARD1 followed the amplitude of the calcium current and thus showed a bell shaped dependence on voltage. In addition, the transient had a slower rate of rise than in pCAC6-injected myotubes and was abolished completely by the addition of Cd2+ + La3+.

scholarly journals The Functional Role of Hyperpolarization Activated Current (If) on Cardiac Pacemaking in Human vs. in the Rabbit Sinoatrial Node: A Simulation and Theoretical Study

2021 ◽  
Vol 12 ◽  
Author(s):  
Xiangyun Bai ◽  
Kuanquan Wang ◽  
Mark R. Boyett ◽  
Jules C. Hancox ◽  
Henggui Zhang
Keyword(s):  
Low Dose ◽  
Sinoatrial Node ◽  
Cell Model ◽  
Bradycardic Agent ◽  
Diastolic Depolarization ◽  
Cardiac Pacemaking ◽  
Resultant Increase ◽  
Model Independent ◽  
Rabbit Sinoatrial Node

The cardiac hyperpolarization-activated “funny” current (If), which contributes to sinoatrial node (SAN) pacemaking, has a more negative half-maximal activation voltage and smaller fully-activated macroscopic conductance in human than in rabbit SAN cells. The consequences of these differences for the relative roles of If in the two species, and for their responses to the specific bradycardic agent ivabradine at clinical doses have not been systematically explored. This study aims to address these issues, through incorporating rabbit and human If formulations developed by Fabbri et al. into the Severi et al. model of rabbit SAN cells. A theory was developed to correlate the effect of If reduction with the total inward depolarising current (Itotal) during diastolic depolarization. Replacing the rabbit If formulation with the human one increased the pacemaking cycle length (CL) from 355 to 1,139 ms. With up to 20% If reduction (a level close to the inhibition of If by ivabradine at clinical concentrations), a modest increase (~5%) in the pacemaking CL was observed with the rabbit If formulation; however, the effect was doubled (~12.4%) for the human If formulation, even though the latter has smaller If density. When the action of acetylcholine (ACh, 0.1 nM) was considered, a 20% If reduction markedly increased the pacemaking CL by 37.5% (~27.3% reduction in the pacing rate), which is similar to the ivabradine effect at clinical concentrations. Theoretical analysis showed that the resultant increase of the pacemaking CL is inversely proportional to the magnitude of Itotal during diastolic depolarization phase: a smaller If in the model resulted in a smaller Itotal amplitude, resulting in a slower pacemaking rate; and the same reduction in If resulted in a more significant change of CL in the cell model with a smaller Itotal. This explained the mechanism by which a low dose of ivabradine slows pacemaking rate more in humans than in the rabbit. Similar results were seen in the Fabbri et al. model of human SAN cells, suggesting our observations are model-independent. Collectively, the results of study explain why low dose ivabradine at clinically relevant concentrations acts as an effective bradycardic agent in modulating human SAN pacemaking.

Relation Between Bicarbonate Concentration and Voltage Dependence of Sodium Currents in Freshly Isolated CA1 Neurons of the Rat

2003 ◽  
Vol 89 (5) ◽  
pp. 2489-2498 ◽  
Author(s):  
C. Bruehl ◽  
O. W. Witte
Keyword(s):  
Membrane Potential ◽  
Voltage Dependence ◽  
Sodium Current ◽  
Calcium Currents ◽  
Sodium Currents ◽  
Bicarbonate Concentration ◽  
Whole Cell ◽  
Ca1 Neurons ◽  
Negative Shift ◽  
Highly Sensitive

It recently has been shown that whole cell calcium and sodium currents are modulated by CO2/HCO[Formula: see text]-buffered saline. While the bicarbonate ion, but not CO2, has been proven to modulate calcium currents, this information is lacking for sodium currents. Furthermore, it is not known whether the strength of modulation dependents on the bicarbonate concentration or whether it is an all-or-nothing phenomenon. To answer these questions, we used the whole cell voltage-clamp technique on freshly isolated hippocampal CA1 neurons from the rat. A voltage step from −130 to −20 mV elicited a sodium current with an amplitude of −5.1 ± 0.5 nA (mean ± SE, n = 17) when cells were superfused with HEPES-buffered saline. The amplitude of this current increased during a subsequent superfusion with solutions containing increasing amounts of bicarbonate and CO2(%CO2/mM HCO[Formula: see text]: 2.5/5.6; 5.0/18; 10/37), with a maximal increment in 10% CO2/37 mM HCO[Formula: see text] of −6.9 ± 0.8 nA. The increase in amplitude was associated with a linear negative shift (slope: −0.7 mV/mM HCO[Formula: see text]) of the potential of half-maximal activation (Δ V h,a: −19.4 ± 1.8 mV in 10% CO2) but not with an alteration in the maximal conductance ( g max: HEPES: 203.1 ± 21.0 nS and 10% CO2/37 mM HCO[Formula: see text]: 207.3 ± 21.3 nS). In addition, the potential of half-maximal inactivation ( V h,i) shifted to more negative potentials (slope: −0.6 mV/mM HCO[Formula: see text]) with increasing amounts of bicarbonate and CO2 (HEPES: −53.6 ± 11.8 mV; 10% CO2/37 mM HCO[Formula: see text]: −69.8 ± 2.1 mV), making the amplitude of the current highly sensitive for small potential changes at resting membrane potential. The same negative shift in voltage dependence arose when cells were exposed to solutions with different amounts of bicarbonate (5.6; 18; 26 mM) but constant CO2(5%) with slope rates of −0.5 mV/mM HCO[Formula: see text] for V h,a and −0.5 mV/mM HCO[Formula: see text] for V h,i. Again, there was no correlation between bicarbonate concentration and the size of g max. When currents were evoked in solutions containing a constant concentration (18 mM) of bicarbonate but different amounts of CO2 (2.5; 5.0 10%), no significant changes have been observed. The present data demonstrate that bicarbonate ions, and not CO2, modulate voltage-gated sodium currents in a concentration-dependent manner. Because the amplitude of the sodium current becomes highly sensitive to membrane potential changes concomitant with increased bicarbonate amounts, this may be critical for the excitability of the neuronal network in situations (like metabolic acidosis, respiratoric alkalosis and hypercapnia) in which the concentration of this ion can alter.

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