Differential Modulation of the Cardiac L- and T-type Calcium Channel Currents by Isoflurane

2001 ◽  
Vol 95 (2) ◽  
pp. 515-524 ◽  
Author(s):  
Amadou K. S. Camara ◽  
Zeljana Begic ◽  
Wai-Meng Kwok ◽  
Zeljko J. Bosnjak
Keyword(s):  
Steady State ◽  
Calcium Channels ◽  
Reversal Potential ◽  
Calcium Currents ◽  
Dependent Manner ◽  
Inotropic Effects ◽  
Phenotypic Differences ◽  
Steady State Inactivation ◽  
Dose Dependent ◽  
Hyperpolarizing Shift

Background Volatile anesthetics exert their negative chronotropic and inotropic effects, in part by depressing the L- and T-type calcium channels. This study examines and compares the dose-dependent effects of isoflurane on atrial L- and T-type calcium currents (I(Ca,L) and I(Ca,T)) and ventricular I(Ca,L). Methods Whole cell I(Ca) was recorded from enzymatically isolated guinea pig cardiomyocytes. Current-voltage relations for atrial and ventricular I(Ca,L) was obtained from holding potentials of -90 and -50 mV to test a potential of +60 mV in 10-mV increments. Atrial I(Ca,T) was determined by subtraction of currents obtained from holding potentials of -50 and -90 mV. Steady state inactivation was determined using standard two-pulse protocols, and data were fitted with the Boltzmann equation. Results Isoflurane depressed I(Ca) in a dose-dependent manner, with Kd values of 0.23+/-0.03, 0.34+/-0.03, and 0.71+/-0.02 mM of anesthetic for atrial I(Ca,T) and I(Ca,L) and ventricular (ICa,L), respectively, and caused a significant (P < 0.05) hyperpolarizing shift in steady state inactivation. At 1.2 and 1.6 mm, isoflurane caused a significant (P < 0.05) depolarizing shift in the steady state activation in ventricular I(Ca,L) but not in atrial I(Ca,L) or I(Ca,T). In addition to the depression of I(Ca,L), isoflurane also induced a hyperpolarizing shift in the reversal potential of I(Ca) for both atrial and ventricular L-type calcium channels. Conclusion The results show that atrial I(Ca,T) is more sensitive to isoflurane than atrial I(Ca,L), and ventricular I(Ca,L) was the least responsive to the anesthetic. These differential sensitivities of the calcium channels in the atrial and ventricular chambers might reflect phenotypic differences in the calcium channels or differences in modulation by the anesthetic.

ω-AgaIVA–Sensitive (P/Q-type) and –Resistant (R-type) High-Voltage–Activated Ba2+ Currents in Embryonic Cockroach Brain Neurons

1999 ◽  
Vol 82 (5) ◽  
pp. 2284-2293 ◽  
Author(s):  
Pascal Benquet ◽  
Janine Le Guen ◽  
Govindan Dayanithi ◽  
Yves Pichon ◽  
François Tiaho
Keyword(s):  
Steady State ◽  
Calcium Channels ◽  
Primary Culture ◽  
High Voltage ◽  
Reversal Potential ◽  
Hill Coefficient ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Brain Neurons ◽  
Voltage Dependent

By means of the whole cell patch-clamp technique, the biophysical and pharmacological properties of voltage-dependent Ba2+ currents ( I Ba) were characterized in embryonic cockroach brain neurons in primary culture. I Ba was characterized by a threshold of approximately −30 mV, a maximum at ∼0 mV, and a reversal potential near +40 mV. Varying the holding potential from −100 to −40 mV did not modify these properties. The steady-state, voltage-dependent activation and inactivation properties of the current were determined by fitting the corresponding curves with the Boltzmann equation and yielded V 0.5 of −10 ± 2 (SE) mV and −30 ± 1 mV, respectively. I Ba was insensitive to the dihydropyridine (DHP) agonist BayK8644 (1 μM) and antagonist isradipine (10 μM) but was efficiently and reversibly blocked by the phenylalkylamine verapamil in a dose-dependent manner ( IC 50 = 170 μM). The toxin ω-CgTxGVIA (1 μM) had no significant effect on IBa. Micromolar doses of ω-CmTxMVIIC were needed to reduce the current amplitude significantly, and the effect was slow. At 1 μM, 38% of the peak current was blocked after 1 h. In contrast, IBa was potently and irreversibly blocked by nanomolar concentrations of ω-AgaTxIVA in ∼81% of the neurons. Approximately 20% of the current was unaffected after treatment of the neurons with high concentrations of the toxin (0.4–1 μM). The steady-state dose-response relationship was fitted with a Hill equation and yielded an IC 50 of 17 nM and a Hill coefficient ( n) of 0.6. A better fit was obtained with a combination of two Hill equations corresponding to specific ( IC 50 = 9 nM; n = 1) and nonspecific ( IC 50 = 900 nM; n = 1) ω-AgaTxIVA–sensitive components. In the remaining 19% of the neurons, concentrations ≥100 nM ω-AgaTxIVA had no visible effect on IBa. On the basis of these results, it is concluded that embryonic cockroach brain neurons in primary culture express at least two types of voltage-dependent, high-voltage–activated (HVA) calcium channels: a specific ω-AgaTxIVA–sensitive component and DHP-, ω-CgTxGVIA–, and ω-AgaTxIVA–resistant component related respectively to the P/Q- and R-type voltage-dependent calcium channels.

Single calcium channels in resistance-sized cerebral arteries from rats

1993 ◽  
Vol 264 (2) ◽  
pp. H470-H478 ◽  
Author(s):  
J. M. Quayle ◽  
J. G. McCarron ◽  
J. R. Asbury ◽  
M. T. Nelson
Keyword(s):  
Steady State ◽  
Calcium Channels ◽  
Single Channel ◽  
Cerebral Arteries ◽  
Membrane Depolarization ◽  
Barium Concentration ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Wistar Kyoto ◽  
Single Calcium Channels

Unitary currents through single calcium channels were measured from cell-attached patches on smooth muscle cells isolated from resistance-sized branches of posterior cerebral arteries from Wistar-Kyoto normotensive rats. Barium (80 and 10 mM) was used as the charge carrier, with and without the dihydropyridine calcium channel agonist BAY R 5417. Unitary currents decreased on membrane depolarization, with a slope conductance of 19.4 pS (80 mM barium). Channel open-state probability (Po) was steeply voltage dependent. Peak Po during test pulses from -70 mV increased e-fold per 4.5-mV depolarization. Mean peak Po at potentials positive to +10 mV was 0.44. Po at steady membrane potentials was also steeply voltage dependent, changing e-fold per 4.5 mV in the absence of inactivation. Steady-state Po at positive potentials was substantially lower than peak Po elicited by test pulses, suggesting that steady-state inactivation can reduce Po by as much as 10-fold. Membrane depolarization decreased the longest mean closed time but had little effect on the mean open time of single calcium channels measured during steady-state recordings. Lowering the external barium concentration from 80 to 10 mM reduced the single channel conductance to 12.4 pS and shifted the relationship between steady-state Po and membrane potential by about -30 mV. BAY R 5417 also shifted this relationship by about -15 mV.

scholarly journals Evidence That Histamine is a Neurotransmitter of Photoreceptors in the Locust Ocellus

1988 ◽  
Vol 138 (1) ◽  
pp. 205-219 ◽  
Author(s):  
PETER J. SIMMONS ◽  
ROGER C. HARDIE
Keyword(s):  
Biogenic Amines ◽  
Reversal Potential ◽  
Outward Current ◽  
Second Order ◽  
Dependent Manner ◽  
Tonic Component ◽  
Hyperpolarizing Response ◽  
Histamine Response ◽  
Dose Dependent ◽  
Initial Peak

The results presented here are consistent with the hypothesis that histamine is the major neurotransmitter released by photoreceptors of locust ocelli. 1. When histamine is injected by ionophoresis into the locust ocellar neuropile, large second-order neurones (L-neurones) hyperpolarize in a dose-dependent manner, and responses to light in these neurones are diminished in amplitude. Both histamine and the illumination of ocellar photoreceptors caused an outward current across the membrane. 2. Hyperpolarizing potentials in L-neurones evoked by histamine had the same reversal potential as hyperpolarizing potentials evoked by photoreceptor illumination. 3. When applied ionophoretically in the ocellus, other biogenic amines, including octopamine, dopamine and noradrenaline, had no effect on the L-neurones. Both gamma-aminobutyricacid and acetylcholine, however, depolarized L-neurones and diminished responses to light. 4. Curare blocked the L-neurone's responses to histamine and light. The histamine response recovered fully. The initial peak hyperpolarizing response to increased light recovered, but the more sustained plateau hyperpolarizing potential did not. 5. Hexamethonium bromide prolonged the response of an L-neurone to histamine, and increased the tonic component of the response to light.

Two types of calcium channels in isolated smooth muscle cells from rat tail artery

1989 ◽  
Vol 256 (5) ◽  
pp. H1361-H1368 ◽  
Author(s):  
R. Wang ◽  
E. Karpinski ◽  
P. K. Pang
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Calcium Channels ◽  
Rat Tail Artery ◽  
Inward Current ◽  
Tail Artery ◽  
Channel Current ◽  
Steady State Inactivation ◽  
Channel Currents ◽  
Rat Tail

Whole cell patch-clamp recordings were carried out on smooth muscle cells from rat tail artery in short-term culture to verify the existence of and to characterize the calcium channels that are present. Two types of voltage-dependent calcium channels were identified in 55 of 63 cells studied. The T-type calcium channel was activated at -50 mV, and the peak inward current occurred at -10 mV, whereas the L-type channel was activated at -20 mV, and the peak inward current occurred at +10 or +20 mV. The T-type channel current inactivated quickly in contrast to the much slower inactivation of the L-channel current. The voltage dependence of steady-state inactivation of the two channels was similar to that reported for other vascular smooth muscle preparations. An internal solution containing Cs2-aspartate maintained the calcium-channel currents for at least 20 min with only a 5-10% decline. BAY K 8644 had no effect on T-channel currents, but the L-channel current was increased by at least a factor of two. In addition, BAY K 8644 shifted the activation threshold, the peak inward current, and the steady-state inactivation-activation curves of L-type channel currents in the direction of hyperpolarization.

Reassessment of primed constant-infusion tracer method to measure urea kinetics

1987 ◽  
Vol 252 (4) ◽  
pp. E557-E564 ◽  
Author(s):  
F. Jahoor ◽  
R. R. Wolfe
Keyword(s):  
Steady State ◽  
Constant Infusion ◽  
Dependent Manner ◽  
Tracer Technique ◽  
Tracer Method ◽  
Priming Dose ◽  
Short Term ◽  
Urea Production ◽  
Urea Kinetics ◽  
Dose Dependent

The validity of the primed constant-infusion tracer technique to make short-term measurements of urea production rates (Ra) in humans in a physiological steady state and during disruption of steady state was evaluated. Four subjects received a primed constant infusion (P/I = 560 min) of [13C]urea for 8 h. A plateau in urea enrichment was reached after 2 h and maintained throughout. When [13C]- and [18O]urea were simultaneously infused into four subjects at P/I ratios of 560:1 and 360:1, respectively, both tracers reached plateau enrichment at the same time (2-4 h). The enrichment at plateau was a function of the infusion rate rather than the priming dose, and calculated urea Ra was the same with either prime. In five additional experiments the technique responded acutely to a physiological perturbation (alanine infusion) in a dose-dependent manner. The results confirm that this technique is appropriate for short-term measurements of urea Ra, and the requirement for accuracy in estimating the priming dose is not impractically stringent.

Effect of cocaine and methylecgonidine on intracellular Ca2+ and myocardial contraction in cardiac myocytes

1997 ◽  
Vol 273 (2) ◽  
pp. H893-H901 ◽  
Author(s):  
L. Huang ◽  
J. H. Woolf ◽  
Y. Ishiguro ◽  
J. P. Morgan
Keyword(s):  
Structural Damage ◽  
Time Course ◽  
Crack Cocaine ◽  
Pyrolysis Product ◽  
Myocardial Contraction ◽  
Dependent Manner ◽  
Response Curves ◽  
Inotropic Effects ◽  
Cell Shortening ◽  
Dose Dependent

We evaluated the cardiac effects of the principle pyrolysis product of crack cocaine smoking, methylecgonidine (MEG), in comparison with cocaine. Peak cell shortening and intracellular Ca2+, as detected by the Ca2+ indicator indo 1, were recorded in enzymatically isolated ferret myocytes. Both cocaine and MEG decreased peak cell shortening and peak intracellular Ca2+ concentration ([Ca2+]i) in a dose-dependent manner (10(-8)-10(-4) M). MEG shifted the peak [Ca2+]i-to-peak shortening relationship downward and was more potent than cocaine. Atropine (10(-6) M) upwardly shifted the dose-response curves of MEG, cocaine, and carbachol but not of procaine. The negative inotropic effects of MEG were inhibited by methoctramine, a selective M2 receptor blocker but not by M1 (pirenzepine) or M3 (4-diphenylacetoxy-N-methylpiperidine methiodide) blocking agents. In contrast to cocaine, the effects of large doses of MEG were irreversible over the time course of our experiments, raising the possibility of structural damage. We conclude that MEG acts primarily on M2 cholinergic receptors in the heart to produce acute cardiac intoxication and, in contrast to cocaine, may decrease the myofilament Ca2+ responseness and cause structural damage to myocytes by a direct toxic effect.

Effects of relaxin on rat atrial myocytes. II. Increased calcium influx derived from action potential prolongation

1997 ◽  
Vol 272 (4) ◽  
pp. H1798-H1803 ◽  
Author(s):  
E. S. Piedras-Renteria ◽  
O. D. Sherwood ◽  
P. M. Best
Keyword(s):  
Action Potential ◽  
Calcium Influx ◽  
Calcium Currents ◽  
Atrial Myocytes ◽  
Inotropic Effects ◽  
Whole Cell Patch Clamp ◽  
Rat Hearts ◽  
Action Potential Prolongation ◽  
Dose Dependent ◽  
Rat Atrial Cells

Relaxin produces positive inotropic and chronotropic effects in rat hearts. The effect of relaxin on the action potential duration (APD) of single quiescent rat atrial cells was investigated with a whole cell patch clamp. Relaxin induced a significant, dose-dependent prolongation of the APD. This effect was maximal at 200 ng/ml (nominal concentration of 33.6 nM), which caused, on average, a 57% increase in the time taken to reach 90% repolarization. The effect of relaxin was blocked by the protein kinase A inhibitor 5-24 amide, indicating that its effect is mediated by an adenosine 3',5'-cyclic monophosphate-dependent mechanism. The increased APD induced by relaxin caused an enhanced entrance of calcium, with the charge carried through voltage-activated calcium channels increased by approximately 25%. This increase was not due to a direct modulation of calcium currents (20); rather, it was a consequence of the longer period of cellular depolarization. Our findings that relaxin increased the APD and therefore increased the calcium influx in atrial myocytes could explain the positive inotropic effects induced by relaxin in atrial preparations.

scholarly journals Biophysical Characterization of Epigallocatechin-3-Gallate Effect on the Cardiac Sodium Channel Nav1.5

Molecules ◽  
2020 ◽  
Vol 25 (4) ◽  
pp. 902 ◽  
Author(s):  
Mohamed-Yassine Amarouch ◽  
Han Kurt ◽  
Lucie Delemotte ◽  
Hugues Abriel
Keyword(s):  
Md Simulations ◽  
Inactivation Kinetics ◽  
Free Energy Barrier ◽  
Dependent Manner ◽  
Biophysical Characterization ◽  
Inactivation Curve ◽  
Cardiac Sodium Channel ◽  
Dependent Inhibition ◽  
Steady State Inactivation ◽  
Dose Dependent

Epigallocatechin-3-Gallate (EGCG) has been extensively studied for its protective effect against cardiovascular disorders. This effect has been attributed to its action on multiple molecular pathways and transmembrane proteins, including the cardiac Nav1.5 channels, which are inhibited in a dose-dependent manner. However, the molecular mechanism underlying this effect remains to be unveiled. To this aim, we have characterized the EGCG effect on Nav1.5 using electrophysiology and molecular dynamics (MD) simulations. EGCG superfusion induced a dose-dependent inhibition of Nav1.5 expressed in tsA201 cells, negatively shifted the steady-state inactivation curve, slowed the inactivation kinetics, and delayed the recovery from fast inactivation. However, EGCG had no effect on the voltage-dependence of activation and showed little use-dependent block on Nav1.5. Finally, MD simulations suggested that EGCG does not preferentially stay in the center of the bilayer, but that it spontaneously relocates to the membrane headgroup region. Moreover, no sign of spontaneous crossing from one leaflet to the other was observed, indicating a relatively large free energy barrier associated with EGCG transport across the membrane. These results indicate that EGCG may exert its biophysical effect via access to its binding site through the cell membrane or via a bilayer-mediated mechanism.

scholarly journals Voltage-dependent inactivation of slow calcium channels in intact twitch muscle fibers of the frog.

1989 ◽  
Vol 94 (5) ◽  
pp. 937-951 ◽  
Author(s):  
G Cota ◽  
E Stefani
Keyword(s):  
Steady State ◽  
Rate Constant ◽  
Voltage Dependence ◽  
Muscle Fibers ◽  
Dependent Manner ◽  
Inactivation Curve ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Intact Muscle ◽  
Ca2 Channels

Inactivation of slow Ca2+ channels was studied in intact twitch skeletal muscle fibers of the frog by using the three-microelectrode voltage-clamp technique. Hypertonic sucrose solutions were used to abolish contraction. The rate constant of decay of the slow Ca2+ current (ICa) remained practically unchanged when the recording solution containing 10 mM Ca2+ was replaced by a Ca2+-buffered solution (126 mM Ca-maleate). The rate constant of decay of ICa monotonically increased with depolarization although the corresponding time integral of ICa followed a bell-shaped function. The replacement of Ca2+ by Ba2+ did not result in a slowing of the rate of decay of the inward current nor did it reduce the degree of steady-state inactivation. The voltage dependence of the steady-state inactivation curve was steeper in the presence of Ba2+. In two-pulse experiments with large conditioning depolarizations ICa inactivation remained unchanged although Ca2+ influx during the prepulse greatly decreased. Dantrolene (12 microM) increased mechanical threshold at all pulse durations tested, the effect being more prominent for short pulses. Dantrolene did not significantly modify ICa decay and the voltage dependence of inactivation. These results indicate that in intact muscle fibers Ca2+ channels inactivate in a voltage-dependent manner through a mechanism that does not require Ca2+ entry into the cell.

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