Activation of reverse Na+-Ca2+exchanger by skeletal Na+channel isoform increases excitation-contraction coupling efficiency in rabbit cardiomyocytes

2020 ◽  
Author(s):  
Natalia S Torres
Keyword(s):  
Action Potentials ◽  
Coupling Efficiency ◽  
Adult Rabbit ◽  
Na Channel ◽  
Channel Coupling ◽  
Contraction Coupling ◽  
Reverse Mode ◽  
Ventricular Cells ◽  
Before And After ◽  
Upstroke Velocity

Our prior work has shown that Na+current (INa) affects sarcoplasmic reticular (SR) Ca2+release by activating early reverse of the Na+-Ca2+exchanger (NCX). The resulting Ca2+ entry primes the dyadic cleft, which appears to increase Ca2+channel coupling fidelity. It has been shown that the skeletalisoform of the voltage-gated Na+channel (Nav1.4) is the main tetrodotoxin(TTX)-sensitive Navisoform expressed in adult rabbit ventricular cardiomyocytes.Here I tested the hypothesis that it is also the principal isoform involved in the priming mechanism. Action potentials (AP) were evoked in isolated rabbit ventricular cells loaded with fluo-4, and simultaneouslyrecorded Ca2+transients before and after the application of either relatively low doses of TTX (100nM),the specific Nav1.4 inhibitor μ-Conotoxin GIIIB or the specific Nav1.1 inhibitor ICA 121430. While AP changes after the application of each drug reflected the relative abundance of each isoform, the effects of TTX and GIIIB on SR Ca2+ release (measured as the transient maximum upstroke velocity) were no different. Furthermore, this reduction in SR Ca2+ release wascomparable to the value that we obtained previously when total INawas inactivated with a ramp applied under voltage clamp. Finally, SR Ca2+ release was unaltered by the same ramp in the presence of TTX or GIIB. In contrast, application of ICA had no effect of SR Ca2+release. Theseresults suggest that Nav1.4 is the main Nav isoform involved in regulating the efficiency ofexcitation-contraction coupling in rabbit cardiomyocytes by priming the junction via activation of reverse-mode NCX.

Basis for tetrodotoxin and lidocaine effects on action potentials in dog ventricular myocytes

1988 ◽  
Vol 254 (6) ◽  
pp. H1157-H1166 ◽  
Author(s):  
J. A. Wasserstrom ◽  
J. J. Salata
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Ventricular Myocytes ◽  
Ionic Currents ◽  
Detectable Effect ◽  
Na Channel ◽  
Na Current ◽  
Voltage Range ◽  
Purkinje Fibers ◽  
Ventricular Cells

We studied the effects of tetrodotoxin (TTX) and lidocaine on transmembrane action potentials and ionic currents in dog isolated ventricular myocytes. TTX (0.1-1 x 10(-5) M) and lidocaine (0.5-2 x 10(-5) M) decreased action potential duration, but only TTX decreased the maximum rate of depolarization (Vmax). Both TTX (1-2 x 10(-5) M) and lidocaine (2-5 x 10(-5) M) blocked a slowly inactivating toward current in the plateau voltage range. The voltage- and time-dependent characteristics of this current are virtually identical to those described in Purkinje fibers for the slowly inactivating inward Na+ current. In addition, TTX abolished the outward shift in net current at plateau potentials caused by lidocaine alone. Lidocaine had no detectable effect on the slow inward Ca2+ current and the inward K+ current rectifier, Ia. Our results indicate that 1) there is a slowly inactivating inward Na+ current in ventricular cells similar in time, voltage, and TTX sensitivity to that described in Purkinje fibers; 2) both TTX and lidocaine shorten ventricular action potentials by reducing this slowly inactivating Na+ current; 3) lidocaine has no additional actions on other ionic currents that contribute to its ability to abbreviate ventricular action potentials; and 4) although both agents shorten the action potential by the same mechanism, only TTX reduces Vmax. This last point suggests that TTX produces tonic block of Na+ current, whereas lidocaine may produce state-dependent Na+ channel block, namely, blockade of Na+ current only after Na+ channels have already been opened (inactivated-state block).

scholarly journals High [Na+]i in cardiomyocytes from rainbow trout

2007 ◽  
Vol 293 (2) ◽  
pp. R861-R866 ◽  
Author(s):  
Rikke Birkedal ◽  
Holly A. Shiels
Keyword(s):  
Rainbow Trout ◽  
Ventricular Myocytes ◽  
Resting Cells ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Contraction Frequency ◽  
Reverse Mode ◽  
Whole Cell Patch Clamp ◽  
Ventricular Cells

Intracellular Na+-concentration, [Na+]i modulates excitation-contraction coupling of cardiac myocytes via the Na+/Ca2+ exchanger (NCX). In cardiomyocytes from rainbow trout ( Oncorhyncus mykiss), whole cell patch-clamp studies have shown that Ca2+ influx via reverse-mode NCX contributes significantly to contraction when [Na+]i is 16 mM but not 10 mM. However, physiological [Na+]i has never been measured. We recorded [Na+]i using the fluorescent indicator sodium-binding benzofuran isophthalate in freshly isolated atrial and ventricular myocytes from rainbow trout. We examined [Na+]i at rest and during increases in contraction frequency across three temperatures that span those trout experience in nature (7, 14, and 21°C). Surprisingly, we found that [Na+]i was not different between atrial and ventricular cells. Furthermore, acute temperature changes did not affect [Na+]i in resting cells. Thus, we report a resting in vivo [Na+]i of 13.4 mM for rainbow trout cardiomyocytes. [Na+]i increased from rest with increases in contraction frequency by 3.2, 4.7, and 6.5% at 0.2, 0.5, and 0.8 Hz, respectively. This corresponds to an increase of 0.4, 0.6, and 0.9 mM at 0.2, 0.5, and 0.8 Hz, respectively. Acute temperature change did not significantly affect the contraction-induced increase in [Na+]i. Our results provide the first measurement of [Na+]i in rainbow trout cardiomyocytes. This surprisingly high [Na+]i is likely to result in physiologically significant Ca2+ influx via reverse-mode NCX during excitation-contraction coupling. We calculate that this Ca2+-source will decrease with the action potential duration as temperature and contraction frequency increases.

Abstract 491: Triggered Sarcoplasmic Reticulum Ca Release Mediated By Na-ca Exchanger And Brain Na Channels In Rabbit Ventricular Cells

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Eleonora Savio-Galimberti ◽  
Joshua I Goldhaber ◽  
John H Bridge
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Action Potentials ◽  
High Probability ◽  
Ryanodine Receptors ◽  
Lower Probability ◽  
Na Channel ◽  
Na Channels ◽  
Triggered Release ◽  
Ventricular Cells ◽  
T Tubules

We tested the hypothesis that sarcoplasmic reticulum (SR) Ca release triggered by cardiac action potentials is significantly affected by Na influx through brain isoforms of the Na channel. These channels are reportedly located in the t-tubules and could therefore activate reverse Na-Ca exchanger (NCX) and contribute to triggered release. In the complete absence of a Na gradient (Li replacement) Ca transients evoked by action potentials were delayed, their upstrokes slowed and their peak values diminished (SR Ca content not depleted under these conditions). Ca spikes recorded under these conditions occurred at significantly lower probability and became asynchronous (see figure ). Tetrodotoxin 200 nM (this concentration selectively blocks brain Na channel isoforms Nav 1.1, 1.3 and 1.6) reduced the magnitude and rate of rise of Ca transients in a way that resembled the effect of removing the Na gradient. We suggest that early activation of brain type Na channels leads to elevation of Na in the dyadic cleft. This causes reverse NCX, which primes the junction with Ca before L-type Ca channels (LCC) have opened. Since the junction has been primed with Ca, short LCC openings can effectively gate ryanodine receptors (RyRs). Because these LCC openings have short latencies and occur with high probability they produce spikes with short latencies at high probability. In the absence of a Na gradient longer LCC openings are required to fill the junction and gate RyRs. These occur with lower probability and greater latency. We conclude that brain Na channels together with NCX significantly increase LCC-RyR coupling fidelity and synchronize spikes.

scholarly journals Effects of mitochondrial uncoupling on Ca2+ signaling during excitation-contraction coupling in atrial myocytes

2013 ◽  
Vol 304 (7) ◽  
pp. H983-H993 ◽  
Author(s):  
Aleksey V. Zima ◽  
Malikarjuna R. Pabbidi ◽  
Stephen L. Lipsius ◽  
Lothar A. Blatter
Keyword(s):  
Ion Homeostasis ◽  
Inhibitory Effect ◽  
Partial Recovery ◽  
Atrial Myocytes ◽  
Mitochondrial Uncoupling ◽  
Release Channel ◽  
Excitation Contraction Coupling ◽  
Atp Production ◽  
Contraction Coupling ◽  
Reverse Mode

Mitochondria play an important role in intracellular Ca2+ concentration ([Ca2+]i) regulation in the heart. We studied sarcoplasmic reticulum (SR) Ca2+ release in cat atrial myocytes during depolarization of mitochondrial membrane potential (ΔΨm) induced by the protonophore FCCP. FCCP caused an initial decrease of action potential-induced Ca2+ transient amplitude and frequency of spontaneous Ca2+ waves followed by partial recovery despite partially depleted SR Ca2+ stores. In the presence of oligomycin, FCCP only exerted a stimulatory effect on Ca2+ transients and Ca2+ wave frequency, suggesting that the inhibitory effect of FCCP was mediated by ATP consumption through reverse-mode operation of mitochondrial F1F0-ATPase. ΔΨm depolarization was accompanied by cytosolic acidification, increases of diastolic [Ca2+]i, intracellular Na+ concentration ([Na+]i), and intracellular Mg2+ concentration ([Mg2+]i), and a decrease of intracellular ATP concentration ([ATP]i); however, glycolytic ATP production partially compensated for the exhaustion of mitochondrial ATP supplies. In conclusion, the initial inhibition of Ca2+ transients and waves resulted from suppression of ryanodine receptor SR Ca2+ release channel activity by a decrease in [ATP], an increase of [Mg2+]i, and cytoplasmic acidification. The later stimulation resulted from reduced mitochondrial Ca2+ buffering and cytosolic Na+ and Ca2+ accumulation, leading to enhanced Ca2+-induced Ca2+ release and spontaneous Ca2+ release in the form of Ca2+ waves. ΔΨm depolarization and the ensuing consequences of mitochondrial uncoupling observed here (intracellular acidification, decrease of [ATP]i, increase of [Na+]i and [Mg2+]i, and Ca2+ overload) are hallmarks of ischemia. These findings may therefore provide insight into the consequences of mitochondrial uncoupling for ion homeostasis, SR Ca2+ release, and excitation-contraction coupling in ischemia at the cellular and subcellular level.

Abstract P498: Polycystin-1 Regulates Excitation-contraction Coupling In Atrial Cardiomyocytes

2021 ◽  
Vol 129 (Suppl_1) ◽  
Author(s):  
Troy Hendrickson ◽  
William Perez ◽  
Vincent Provasek ◽  
Francisco J Altamirano
Keyword(s):  
Electrical Stimulation ◽  
Action Potentials ◽  
Primary Cilia ◽  
Calcium Influx ◽  
Calcium Transient ◽  
Calcium Handling ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Atrial Cardiomyocytes ◽  
Atrial Excitation

Patients with Autosomal Dominant Polycystic Kidney disease (ADPKD) have multiple cardiovascular manifestations, including increased susceptibility to arrhythmias. Mutations in polycystin-1 (PC1) encoding gene accounts for 85% cases of ADPKD, whereas mutations in polycystin-2 (PC2) only accounts for 15%. In kidney cells, PC1 interacts with PC2 to form a protein complex at the primary cilia to regulate calcium influx via PC2. However, cardiomyocytes are non-ciliated cells and the role of both PC1 and PC2 in atrial cardiomyocytes remains unknown. We have previously demonstrated that PC1 regulates action potentials and calcium handling to fine-tune ventricular cardiomyocyte contraction. Here, we hypothesize that PC1 regulates action potentials and calcium handling in atrial cardiomyocytes independent of PC2 actions. To test this hypothesis, we differentiated human induced pluripotent stem cells (iPSC) into atrial cardiomyocytes (iPSC-aCM) using previously published protocols. To determine the contribution of PC1/PC2 in atrial excitation-contraction coupling, protein expression was knocked down utilizing specific siRNA constructs, for each protein, or a universal control siRNA transfected using lipofectamine RNAiMAX. We measured action potentials using the potentiometric dye FluoVolt and intracellular calcium with Fura-2 AM or Fluo-4. Changes in fluorescence were monitored using a multiwavelength IonOptix system. iPSC-aCM were paced at 2 Hz to synchronize the beating pattern using field electrical stimulation. Our data shows that PC1 ablation significantly decreased action potential duration at 50% and 80% of repolarization, by 24% and 23%, respectively. Moreover, we observed that PC1 knockdown significantly reduced calcium transient amplitude elicited by field electrical stimulation without changes in calcium transient decay. Interestingly, PC2 knockdown did not modify calcium transients in atrial cardiomyocytes (iPSC-aCM). Our data suggest that PC1 regulates atrial excitation-contraction coupling independent of PC2 actions. This study warrants further investigation into atrial dysfunction in ADPKD patients with PC1 mutations.

CYCLIC AMP STIMULATION OF ELECTROGENIC UPTAKE OF Na+ AND Cl- ACROSS THE GILL EPITHELIUM OF THE CHINESE CRAB ERIOCHEIR SINENSIS

1994 ◽  
Vol 188 (1) ◽  
pp. 159-174 ◽  
Author(s):  
S Riestenpatt ◽  
W Zeiske ◽  
H Onken
Keyword(s):  
Cyclic Amp ◽  
Electromotive Force ◽  
Single Channel ◽  
Short Circuit ◽  
Ussing Chamber ◽  
Eriocheir Sinensis ◽  
Na Channel ◽  
Before And After ◽  
Gill Lamellae ◽  
Stimulation Of

Split gill lamellae (epithelium plus cuticle) of hyperregulating Chinese crabs acclimated to fresh water were mounted in a modified Ussing chamber. Active and electrogenic absorption of sodium and chloride were measured as positive amiloride-sensitive and negative Cl--dependent short-circuit currents (INa, ICl), respectively. Both currents were characterized before and after treatment of the tissue with theophylline or dibutyryl cyclic AMP. Both drugs increased INa and ICl. A simple circuit analysis showed that INa stimulation reflected a marked increase in the transcellular Na+ conductance, whereas the respective electromotive force was unchanged. The Michaelis constant (KNa) for Na+ current saturation was decreased after INa stimulation, indicating an increased affinity of the transport mechanism for its substrate. Consequently, the affinity for the Na+ channel blocker amiloride decreased as expected for a competitive interaction between substrate and inhibitor. Analysis of the amiloride-induced current-noise revealed a marked increase in the number of apical Na+ channels after INa stimulation with theophylline, whereas there was little change in the single-channel current. Stimulation of Cl- absorption was accompanied by a substantial increase in both transcellular conductance and electromotive force, indicating an activation of the apical H+ pump that provides the driving force for active Cl- uptake via apical Cl-/HCO3- exchange and basolateral Cl- channels.

Neuroprotective Effects of Increased Extracellular Ca2+ During Aglycemia in White Matter

2002 ◽  
Vol 88 (3) ◽  
pp. 1302-1307 ◽  
Author(s):  
Angus M. Brown ◽  
Bruce R. Ransom
Keyword(s):  
Action Potentials ◽  
Divalent Cations ◽  
Neuroprotective Effects ◽  
Adult Rat ◽  
Artificial Cerebrospinal Fluid ◽  
Before And After ◽  
Compound Action Potentials ◽  
Compound Action

We investigated the effects of extracellular [Ca2+] ([Ca2+]o) on aglycemia-induced dysfunction and injury in adult rat optic nerves. Compound action potentials (CAPs) from adult rat optic nerve were recorded in vitro, and the area under the CAP was used to monitor nerve function before and after 1 h periods of aglycemia. In control artificial cerebrospinal fluid (ACSF) containing 2 mM Ca2+, CAP function fell after 29.9 ± 1.5 (SE) min and recovered to 48.8 ± 3.9% following aglycemia. Reducing bath [Ca2+] during aglycemia progressively improved recovery. For example, in Ca2+-free ACSF, the CAP recovered to 99.1 ± 3.8%. Paradoxically, increasing bath [Ca2+] also improved recovery from aglycemia. In 5 or 10 mM bath [Ca2+], CAP recovered to 78.8 ± 9.2 or 91.6 ± 5.2%, respectively. The latency to CAP failure during aglycemia increased as a function of bath [Ca2+] from 0 to 10 mM. Increasing bath [Mg2+] from 2 to 5 or 10 mM, with bath [Ca2+] held at 2 mM, increased latency to CAP failure with aglycemia and improved recovery from this insult. [Ca2+]o recorded with calcium-sensitive microelectrodes in control ACSF, dropped reversibly during aglycemia from 1.54 ± 0.03 to 0.45 ± 0.04 mM. In the presence of higher ambient levels of bath [Ca2+] (i.e., 5 or 10 mM), the aglycemia-induced decrease in [Ca2+]o declined, indicating that less Ca2+ left the extracellular space to enter an intracellular compartment. These results indicate that the role of [Ca2+], and divalent cations in general, during aglycemia is complex. While extracellular Ca2+ was required for irreversible aglycemic injury to occur, higher levels of [Ca2+] or [Mg2+] increased the latency to CAP failure and improved the extent of recovery, apparently by limiting Ca2+ influx. These effects are theorized to be mediated by divalent cation screening.

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