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+.

Simulated ischemia enhances L-type calcium current in pacemaker cells isolated from the rabbit sinoatrial node

2007 ◽  
Vol 293 (5) ◽  
pp. H2986-H2994 ◽  
Author(s):  
Yi-Mei Du ◽  
Richard D. Nathan
Keyword(s):  
Steady State ◽  
Sinoatrial Node ◽  
Atrial Myocytes ◽  
Pacemaker Cells ◽  
Activation Curve ◽  
Positive Direction ◽  
Inactivation Curve ◽  
Steady State Inactivation ◽  
Rabbit Sinoatrial Node ◽  
Maximum Conductance

Ischemic-like conditions (a glucose-free, pH 6.6 Tyrode solution bubbled with 100% N2) enhance L-type Ca current ( ICa,L) in single pacemaker cells (PCs) isolated from the rabbit sinoatrial node (SAN). In contrast, studies of ventricular myocytes have shown that acidic extracellular pH, as employed in our “ischemic” Tyrode, reduces ICa,L. Therefore, our goal was to explain why ICa,L is increased by “ischemia” in SAN PCs. The major findings were the following: 1) blockade of Ca-induced Ca release with ryanodine, exposure of PCs to BAPTA-AM, or replacement of extracellular Ca2+ with Ba2+ failed to prevent the ischemia-induced enhancement of ICa,L; 2) inhibition of protein kinase A with H-89, or calcium/calmodulin-dependent protein kinase II with KN-93, reduced ICa,L but did not prevent its augmentation by ischemia; 3) ischemic Tyrode or pH 6.6 Tyrode shifted the steady-state inactivation curve in the positive direction, thereby reducing inactivation; 4) ischemic Tyrode increased the maximum conductance but did not affect the activation curve; 5) in rabbit atrial myocytes isolated and studied with exactly the same techniques used for SAN PCs, ischemic Tyrode reduced the maximum conductance and shifted the activation curve in the positive direction; pH 6.6 Tyrode also shifted the steady-state inactivation curve in the positive direction. We conclude that the acidic pH of ischemic Tyrode enhances ICa,L in SAN PCs, because it increases the maximum conductance and reduces inactivation. Furthermore, the opposite results obtained with rabbit atrial myocytes cannot be explained by differences in cell isolation or patch-clamp techniques.

Multiple calcium currents in a thyroid C-cell line: biophysical properties and pharmacology

1991 ◽  
Vol 260 (6) ◽  
pp. C1253-C1263 ◽  
Author(s):  
B. A. Biagi ◽  
J. J. Enyeart
Keyword(s):  
Cell Line ◽  
Time Constant ◽  
Calcium Currents ◽  
C Cells ◽  
Patch Clamp Technique ◽  
C Cell ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
Rat Thyroid ◽  
Ca2 Channels

The whole cell version of the patch-clamp technique was used to characterize voltage-gated Ca2+ channels in the calcitonin-secreting rat thyroid C-cell line 6-23 (clone 6). Three types of Ca2+ channels could be distinguished based on differences in voltage dependence, kinetics, and pharmacological sensitivity. T-type current was half-maximal at -31 mV, showed steady-state voltage-dependent inactivation that was half-maximal at -57 mV, inactivated with a voltage-dependent time constant that reached a minimum of 20 ms at potentials positive to -20 mV, and deactivated with a single time constant of approximately 2 ms at -80 mV. Reactivation of inactivated channels occurred with a time constant of 1.26 s at -90 mV. T current was selectively blocked by Ni2+ at concentrations between 5 and 50 microM. La3+ and Y3+ blocked the T current at 10- to 20-fold lower concentrations. Dihydropyridine-sensitive L-type current was half-maximal at a test potential of -3 mV and was approximately doubled in size when Ba2+ replaced Ca2+ as the charge carrier. Unlike L-type Ca2+ current in many cells, this current in C-cells displayed little Ca(2+)-dependent inactivation. N-type current was composed of inactivating and sustained components that were inhibited by omega-conotoxin. The inactivating component was half-maximal at +9 mV and could be fitted by two exponentials with time constants of 22 and 142 ms. A slow inactivation of N current with a time constant of 24.9 s was observed upon switching the holding potential from -80 to -40 mV. These results demonstrate that, similar to other neural crest derived cells, thyroid C-cells express multiple Ca2+ channels, including one previously observed only in neurons.

Functional Expression of L-, N-, P/Q-, and R-Type Calcium Channels in the Human NT2-N Cell Line

2000 ◽  
Vol 84 (6) ◽  
pp. 2933-2944 ◽  
Author(s):  
Torben R. Neelands ◽  
Anthony P. J. King ◽  
Robert L. Macdonald
Keyword(s):  
Calcium Channel ◽  
Cell Line ◽  
Functional Expression ◽  
Calcium Currents ◽  
Channel Blockers ◽  
Patch Clamp Technique ◽  
Teratocarcinoma Cell ◽  
Inactivation Curve ◽  
Whole Cell ◽  
Channel Currents

The biophysical and pharmacological properties of voltage-gated calcium channel currents in the human teratocarcinoma cell line NT2-N were studied using the whole cell patch-clamp technique. When held at −80 mV, barium currents ( I Bas) were evoked by voltage commands to above −35 mV that peaked at +5 mV. When holding potentials were reduced to −20 mV or 5 mM barium was substituted for 5 mM calcium, there was a reduction in peak currents and a right shift in the current-voltage curve. A steady-state inactivation curve for I Ba was fit with a Boltzmann curve ( V 1/2 = −43.3 mV; slope = −17.7 mV). Maximal current amplitude increased from 1-wk (232 pA) to 9-wk (1025 pA) postdifferentiation. Whole cell I Bas were partially blocked by specific channel blockers to a similar extent in 1- to 3-wk and 7- to 9-wk postdifferentiation NT2-N cells: 10 μM nifedipine (19 vs. 25%), 10 μM conotoxin GVIA (27 vs. 25%), 10 μM conotoxin MVIIC (15 vs. 16%), and 1.75 μM SNX-482 (31 vs. 33%). Currents were completely blocked by 300 μM cadmium. In the presence of nifedipine, GVIA, and MVIIC, ∼35% of current remained, which was reduced further by SNX-482 (7–14% of current remained), consistent with functional expression of L-, N-, and P/Q-calcium channel types and one or more R-type channel. The presence of multiple calcium currents in this human neuronal-type cell line provides a potentially useful model for study of the regulation, expression and cellular function of human derived calcium channel currents; in particular the R-type current(s).

A mathematical model of a rabbit sinoatrial node cell

1994 ◽  
Vol 266 (3) ◽  
pp. C832-C852 ◽  
Author(s):  
S. S. Demir ◽  
J. W. Clark ◽  
C. R. Murphey ◽  
W. R. Giles
Keyword(s):  
Mathematical Model ◽  
Sinoatrial Node ◽  
Surface Membrane ◽  
Recent Experimental Data ◽  
Pacemaker Cells ◽  
Diffusion Limited ◽  
Electrophysiological Responses ◽  
Sinoatrial Node Cell ◽  
Rabbit Sinoatrial Node

A mathematical model for the electrophysiological responses of a rabbit sinoatrial node cell that is based on whole cell recordings from enzymatically isolated single pacemaker cells at 37 degrees C has been developed. The ion channels, Na(+)-K+ and Ca2+ pumps, and Na(+)-Ca2+ exchanger in the surface membrane (sarcolemma) are described using equations for these known currents in mammalian pacemaker cells. The extracellular environment is treated as a diffusion-limited space, and the myoplasm contains Ca(2+)-binding proteins (calmodulin and troponin). Original features of this model include 1) new equations for the hyperpolarization-activated inward current, 2) assessment of the role of the transient-type Ca2+ current during pacemaker depolarization, 3) inclusion of an Na+ current based on recent experimental data, and 4) demonstration of the possible influence of pump and exchanger currents and background currents on the pacemaker rate. This model provides acceptable fits to voltage-clamp and action potential data and can be used to seek biophysically based explanations of the electrophysiological activity in the rabbit sinoatrial node cell.

Heterogeneity of 4-aminopyridine-sensitive current in rabbit sinoatrial node cells

1999 ◽  
Vol 276 (4) ◽  
pp. H1295-H1304 ◽  
Author(s):  
Haruo Honjo ◽  
Ming Lei ◽  
Mark R. Boyett ◽  
Itsuo Kodama
Keyword(s):  
Membrane Potential ◽  
Regional Differences ◽  
Sinoatrial Node ◽  
Pacemaker Cells ◽  
Electrophysiological Properties ◽  
Sa Node ◽  
Slope Factor ◽  
Ionic Mechanisms ◽  
Rabbit Sinoatrial Node ◽  
Cell Capacitance

The electrophysiological properties of sinoatrial (SA) node pacemaker cells vary in different regions of the node. In this study, we have investigated variation of the 4-aminopyridine (4-AP)-sensitive current as a function of the size (as measured by the cell capacitance) of SA node cells to elucidate the ionic mechanisms. The 10 mM 4-AP-sensitive current recorded from rabbit SA node cells was composed of transient and sustained components ( I trans and I sus, respectively). The activation and inactivation properties [activation: membrane potential at which conductance is half-maximally activated ( V h) = 19.3 mV, slope factor ( k) = 15.0 mV; inactivation: V h= −31.5 mV, k = 7.2 mV] as well as the density of I trans (9.0 pA/pF on average at +50 mV) were independent of cell capacitance. In contrast, the density of I sus (0.97 pA/pF on average at +50 mV) was greater in larger cells, giving rise to a significant correlation with cell capacitance. The greater density of I sus in larger cells (presumably from the periphery) can explain the shorter action potential in the periphery of the SA node compared with that in the center. Thus variation of the 4-AP-sensitive current may be involved in regional differences in repolarization within the SA node.

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 Negative chronotropic actions of endothelin-1 on rabbit sinoatrial node pacemaker cells

1997 ◽  
Vol 122 (2) ◽  
pp. 321-329 ◽  
Author(s):  
Hideo Tanaka ◽  
Yoshizumi Habuchi ◽  
Taku Yamamoto ◽  
Manabu Nishio ◽  
Junichiro Morikawa ◽  
...  
Keyword(s):  
Sinoatrial Node ◽  
Pacemaker Cells ◽  
Endothelin 1 ◽  
Rabbit Sinoatrial Node
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