scholarly journals Lipopolysaccharides directly decrease Ca2+ oscillations and the hyperpolarization-activated nonselective cation current If in immortalized HL-1 cardiomyocytes

2010 ◽  
Vol 299 (3) ◽  
pp. C665-C671 ◽  
Author(s):  
Robert Wondergem ◽  
Bridget M. Graves ◽  
Tammy R. Ozment-Skelton ◽  
Chuanfu Li ◽  
David L. Williams
Keyword(s):  
Heart Failure ◽  
Calcium Metabolism ◽  
Salmonella Enteritidis ◽  
Cardiac Myocyte ◽  
Reversal Potential ◽  
Cell Voltage ◽  
Pacemaker Current ◽  
Cation Current ◽  
Intracellular Ca ◽  
Myocyte Function

Lipopolysaccharide (LPS) has been implicated in sepsis-mediated heart failure and chronic cardiac myopathies. We determined that LPS directly and reversibly affects cardiac myocyte function by altering regulation of intracellular Ca2+ concentration ([Ca2+]i) in immortalized cardiomyocytes, HL-1 cells. [Ca2+]i oscillated (<0.4 Hz), displaying slow and transient components. LPS (1 μg/ml), derived either from Escherichia coli or from Salmonella enteritidis , reversibly abolished Ca2+ oscillations and decreased basal [Ca2+]i by 30–40 nM. HL-1 cells expressed Toll-like receptors, i.e., TLR-2 and TLR-4. Thus, we differentiated effects of LPS on [Ca2+]i and Ca2+ oscillations by addition of utlrapure LPS, a TLR-4 ligand. Ultrapure LPS had no effect on basal [Ca2+]i, but it reduced the rate of Ca2+ oscillations. Interestingly, Pam3CSK4, a TLR-2 ligand, affected neither Ca2+ parameter, and the effect of ultrapure LPS and Pam3CSK4 combined was similar to that of utlrapure LPS alone. Thus, unpurified LPS directly inhibits HL-1 calcium metabolism via TLR-4 and non-TLR-4-dependent mechanisms. Since others have shown that endotoxin impairs the hyperpolarization-activated, nonselective cationic pacemaker current ( If), which is expressed in HL-1 cells, we utilized whole cell voltage-clamp techniques to demonstrate that LPS (1 μg/ml) reduced If in HL-1 cells. This inhibition was marginal at physiologic membrane potentials and significant at very negative potentials ( P < 0.05 at −140, −150, and −160 mV). So, we also evaluated effects of LPS on tail currents of fully activated If. LPS reduced the slope conductance of the tail currents from 498 ± 140 pS/pF to 223 ± 65 pS/pF ( P < 0.05) without affecting reversal potential of −11 mV. Ultrapure LPS had similar effect on If, whereas Pam3CSK4 had no effect on If. We conclude that LPS inhibits activation of If, enhances its deactivation, and impairs regulation of [Ca2+]i in HL-1 cardiomyocytes via TLR-4 and other mechanisms.

Zn2+ Blocks the NMDA- and Ca2+-Triggered Postexposure Current I pe in Hippocampal Pyramidal Cells

1998 ◽  
Vol 79 (2) ◽  
pp. 1124-1126 ◽  
Author(s):  
Qiang X. Chen ◽  
Katherine L. Perkins ◽  
Robert K. S. Wong
Keyword(s):  
Divalent Cations ◽  
Pyramidal Cells ◽  
Cell Voltage ◽  
Continuous Growth ◽  
Ca1 Pyramidal Cells ◽  
Cation Current ◽  
Hippocampal Ca1 ◽  
Intracellular Ca ◽  
Hippocampal Pyramidal Cells

Chen, Qiang X., Katherine L. Perkins, and Robert K. S. Wong. Zn2+ blocks the NMDA- and Ca2+-triggered postexposure current I pe in hippocampal pyramidal cells. J. Neurophysiol. 79: 1124–1126, 1998. Whole cell voltage-clamp recordings from acutely isolated hippocampal CA1 pyramidal cells from adult guinea pigs were used to evaluate divalent cations as possible blockers of the postexposure current ( I pe). I pe is a cation current that is triggered by the rise in intracellular Ca2+ concentration that occurs after the application of a toxic level of N-methyl-d-aspartate (NMDA). Once triggered, I pe continues to grow until death of the neuron occurs. I pe may be a critical link between transient NMDA exposure and cell death. I pe was blocked by micromolar concentrations of Zn2+. The Zn2+ effect had an IC50 of 64 μM and saturated at 500 μM. Prolonged Zn2+ block of I pe revealed that the maintenance of a steady I pe is not dependent on I pe-mediated Ca2+ influx but that the continuous growth in I pe is dependent on I pe-mediated Ca2+ influx. The availability of an effective blocker of I pe should facilitate the investigation of the intracellular activation pathway of I pe and the role of I pe in neuronal death.

Mitochondrial Ca2+ Activates a Cation Current in Aplysia Bag Cell Neurons

2010 ◽  
Vol 103 (3) ◽  
pp. 1543-1556 ◽  
Author(s):  
Charlene M. Hickey ◽  
Julia E. Geiger ◽  
Chris J. Groten ◽  
Neil S. Magoski
Keyword(s):  
Endoplasmic Reticulum ◽  
Ion Channels ◽  
Time Course ◽  
Reversal Potential ◽  
Neuroendocrine Cells ◽  
Dependent Manner ◽  
Inward Current ◽  
Cation Current ◽  
Intracellular Ca ◽  
Bag Cell Neurons

Ion channels may be gated by Ca2+ entering from the extracellular space or released from intracellular stores—typically the endoplasmic reticulum. The present study examines how Ca2+ impacts ion channels in the bag cell neurons of Aplysia californica. These neuroendocrine cells trigger ovulation through an afterdischarge involving Ca2+ influx from Ca2+ channels and Ca2+ release from both the mitochondria and endoplasmic reticulum. Liberating mitochondrial Ca2+ with the protonophore, carbonyl cyanide-4-trifluoromethoxyphenyl-hydrazone (FCCP), depolarized bag cell neurons, whereas depleting endoplasmic reticulum Ca2+ with the Ca2+-ATPase inhibitor, cyclopiazonic acid, did not. In a concentration-dependent manner, FCCP elicited an inward current associated with an increase in conductance and a linear current/voltage relationship that reversed near −40 mV. The reversal potential was unaffected by changing intracellular Cl−, but left-shifted when extracellular Ca2+ was removed and right-shifted when intracellular K+ was decreased. Strong buffering of intracellular Ca2+ decreased the current, although the response was not altered by blocking Ca2+-dependent proteases. Furthermore, fura imaging demonstrated that FCCP elevated intracellular Ca2+ with a time course similar to the current itself. Inhibiting either the V-type H+-ATPase or the ATP synthetase failed to produce a current, ruling out acidic Ca2+ stores or disruption of ATP production as mechanisms for the FCCP response. Similarly, any involvement of reactive oxygen species potentially produced by mitochondrial depolarization was mitigated by the fact that dialysis with xanthine/xanthine oxidase did not evoke an inward current. However, both the FCCP-induced current and Ca2+ elevation were diminished by disabling the mitochondrial permeability transition pore with the alkylating agent, N-ethylmaleimide. The data suggest that mitochondrial Ca2+ gates a voltage-independent, nonselective cation current with the potential to drive the afterdischarge and contribute to reproduction. Employing Ca2+ from mitochondria, rather than the more common endoplasmic reticulum, represents a diversification of the mechanisms that influence neuronal activity.

Activation of a Calcium-Activated Cation Current During Epileptiform Discharges and Its Possible Role in Sustaining Seizure-Like Events in Neocortical Slices

2004 ◽  
Vol 92 (2) ◽  
pp. 862-872 ◽  
Author(s):  
Yitzhak Schiller
Keyword(s):  
Brain Slices ◽  
Reversal Potential ◽  
Cell Voltage ◽  
Epileptic Seizures ◽  
Flufenamic Acid ◽  
Calcium Stores ◽  
Epileptiform Discharges ◽  
Cation Current ◽  
Paroxysmal Depolarization Shift ◽  
Internal Calcium

Epileptic seizures are composed of recurrent bursts of intense firing separated by periods of electrical quiescence. The mechanisms responsible for sustaining seizures and generating recurrent bursts are yet unclear. Using whole cell voltage recordings combined with intracellular calcium fluorescence imaging from bicuculline (BCC)-treated neocortical brain slices, I showed isolated paroxysmal depolarization shift (PDS) discharges were followed by a sustained afterdepolarization waveform (SADW) with an average peak amplitude of 3.3 ± 0.9 mV and average half-width of 6.2 ± 0.6 s. The SADW was mediated by the calcium-activated nonspecific cation current ( Ican) as it had a reversal potential of –33.1 ± 6.8 mV, was unaffected by changing the intracellular chloride concentrations, was markedly diminished by buffering [Ca2+]i with intracellular bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid (BAPTA), and was reversibly abolished by the Ican blocker flufenamic acid (FFA). The Ca2+ influx responsible for activation of Ican was mediated by both N-methyl-d-aspartate-receptor channels, voltage-gated calcium channels and, to a lesser extent, internal calcium stores. In addition to isolated PDS discharges, BCC-treated brain slices also produced seizure-like events, which were accompanied by a prolonged depolarizing waveform underlying individual ictal bursts. The similarities between the initial part of this waveform and the SADW and the fact it was markedly reduced by buffering [Ca2+]i with BAPTA strongly suggested it was mediated, at least in part, by Ican. Addition of FFA reversibly eliminated recurrent bursting, and transformed seizure-like events into isolated PDS responses. These results indicated Ican was activated during epileptiform discharges and probably participated in sustaining seizure-like events.

Role of gelsolin in the actin filament regulation of cardiac L-type calcium channels

1999 ◽  
Vol 277 (6) ◽  
pp. C1277-C1283 ◽  
Author(s):  
Alan S. Lader ◽  
David J. Kwiatkowski ◽  
Horacio F. Cantiello
Keyword(s):  
Calcium Channel ◽  
Actin Filament ◽  
Cardiac Myocyte ◽  
Cell Function ◽  
Supermolecular Structure ◽  
Cell Voltage ◽  
Wild Type ◽  
Calcium Channel Inactivation ◽  
Myocyte Function

The actin cytoskeleton is an important contributor to the modulation of the cell function. However, little is known about the regulatory role of this supermolecular structure in the membrane events that take place in the heart. In this report, the regulation of cardiac myocyte function by actin filament organization was investigated in neonatal mouse cardiac myocytes (NMCM) from both wild-type mice and mice genetically devoid of the actin filament severing protein gelsolin (Gsn−/−). Cardiac L-type calcium channel currents ( I Ca) were assessed using the whole cell voltage-clamp technique. Addition of the actin filament stabilizer phalloidin to wild-type NMCM increased I Ca by 227% over control conditions. The basal I Ca of Gsn−/− NMCM was 300% higher than wild-type controls. This increase was completely reversed by intracellular perfusion of the Gsn−/− NMCM with exogenous gelsolin. Further, cytoskeletal disruption of either Gsn−/− or phalloidin-dialyzed wild-type NMCM with cytochalasin D (CD) decreased the enhanced I Ca by 84% and 87%, respectively. The data indicate that actin filament stabilization by either a lack of gelsolin or intracellular dialysis with phalloidin increase I Ca, whereas actin filament disruption with CD or dialysis of Gsn−/− NMCM with gelsolin decrease I Ca. We conclude that cardiac L-type calcium channel regulation is tightly controlled by actin filament organization. Actin filament rearrangement mediated by gelsolin may contribute to calcium channel inactivation.

Role of nonselective cation current in muscarinic responses of canine colonic muscle

1993 ◽  
Vol 265 (6) ◽  
pp. C1463-C1471 ◽  
Author(s):  
H. K. Lee ◽  
O. Bayguinov ◽  
K. M. Sanders
Keyword(s):  
Divalent Cations ◽  
Reversal Potential ◽  
Outward Current ◽  
Cell Voltage ◽  
Isolated Cells ◽  
Cation Current ◽  
Cation Conductance ◽  
Voltage Dependent ◽  
Patch Technique

The mechanism of muscarinic excitation was studied in colonic muscle strips and isolated cells. In whole cell voltage-clamp studies performed at 33 degrees C utilizing the permeabilized patch technique, acetylcholine (ACh) reduced an L-type Ca2+ current. With K+ currents blocked, depolarization to positive potentials in the presence of ACh elicited outward current. Difference currents showed that ACh activated a voltage-dependent current that reversed at about -8 mV; this current (IACh) had properties similar to the nonselective cation conductance found in other smooth muscle cells. The reversal potential of IACh shifted toward negative potentials when external Na+ was reduced, and the inward current elicited at -70 mV decreased when external Na+ was reduced. IACh was facilitated by internal Ca2+. After the current was activated at a holding potential of -70 mV, depolarizations to -30 to 0 mV elicited influx of Ca2+ via voltage-dependent Ca2+ channels. After repolarization to the holding potential, a large inward tail current was observed. IACh was blocked by Ni2+ and Cd2+ at concentrations of 100 microM or less. Quinine (0.5 mM) also blocked IACh. With the use of the sensitivity of IACh to reduced external Na+ and divalent cations, the role of IACh in responses of intact muscles to ACh was examined. When external Na+ was reduced, ACh failed to increase slow-wave duration, and Ni2+ (50 microM) reversed the depolarization caused by ACh. These data suggest an important role for IACh in the electrical responses of colonic muscles. The contribution of IACh appears to prolong slow waves, which would allow greater entry of Ca2+ and increased force development.

scholarly journals Immune Cells and Immunotherapy for Cardiac Injury and Repair

2021 ◽  
Vol 128 (11) ◽  
pp. 1766-1779
Author(s):  
Joel G. Rurik ◽  
Haig Aghajanian ◽  
Jonathan A. Epstein
Keyword(s):  
Heart Failure ◽  
Immune Cells ◽  
Cardiac Fibrosis ◽  
Cardiac Myocyte ◽  
Cardiac Injury ◽  
Therapeutic Interventions ◽  
Acute Injury ◽  
Myocyte Function ◽  
New Treatment ◽  
Injury And Repair

Cardiac injury remains a major cause of morbidity and mortality worldwide. Despite significant advances, a full understanding of why the heart fails to fully recover function after acute injury, and why progressive heart failure frequently ensues, remains elusive. No therapeutics, short of heart transplantation, have emerged to reliably halt or reverse the inexorable progression of heart failure in the majority of patients once it has become clinically evident. To date, most pharmacological interventions have focused on modifying hemodynamics (reducing afterload, controlling blood pressure and blood volume) or on modifying cardiac myocyte function. However, important contributions of the immune system to normal cardiac function and the response to injury have recently emerged as exciting areas of investigation. Therapeutic interventions aimed at harnessing the power of immune cells hold promise for new treatment avenues for cardiac disease. Here, we review the immune response to heart injury, its contribution to cardiac fibrosis, and the potential of immune modifying therapies to affect cardiac repair.

GABA-Activated Conductance in Cultured Rat Inferior Colliculus Neurons

1997 ◽  
Vol 77 (2) ◽  
pp. 994-1002 ◽  
Author(s):  
Hidenobu Hosomi ◽  
Masahiro Mori ◽  
Mutsuo Amatsu ◽  
Yasuhiro Okada
Keyword(s):  
Inferior Colliculus ◽  
Voltage Clamp ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
External Solution ◽  
Cell Voltage ◽  
Equilibrium Potential ◽  
Fluorescence Measurements ◽  
Intracellular Ca ◽  
Induced Currents

Hosomi, Hidenobu, Masahiro Mori, Mutsuo Amatsu, and Yasuhiro Okada. GABA-activated conductance in cultured rat inferior colliculus neurons. J. Neurophysiol. 77: 994–1002, 1997. With the use of a whole cell voltage-clamp technique and fura-2 fluorescence measurements, the actions of γ-aminobutyric acid (GABA) on cultured neurons from rat inferior colliculus were investigated. GABA (10–1,000 μM) induced currents in neurons held under voltage clamp that were inhibited by bicuculline (20 μM). Muscimol (100 μM) also evoked the currents, whereas baclofen (100 μM) affected neither the holding currents nor K+ conductance due to depolarizing pulses. The current density–voltage relation of GABA-induced currents, with equal concentrations of Cl− in the internal and external solutions, reversed near 0 mV. Reduction of the internal Cl− concentration shifted the reversal potential in the negative direction as predicted from the Cl− equilibrium potential. Baclofen did not affect Ca2+ conductance due to depolarizing pulses. The extracellular application of 150 mM KCl or 1.0 mM glutamate increased the intracellular Ca2+ concentration ([Ca2+]i) of cultured inferior colliculus neurons only when neurons were bathed in a Ca2+-containing external solution. However, GABA (1.0 mM) failed to increase [Ca2+]i at all concentrations of external Ca2+ used, indicating that GABA neither depolarized the cultured inferior colliculus neurons sufficiently to activate the voltage-dependent Ca2+ conductances nor evoked Ca2+ release from intracellular stores. These results suggest that in cultured rat inferior colliculus neurons, GABAA receptor channels may be predominantly responsible for the membrane conductance evoked by GABA and subsequent hyperpolarization of the neurons.

Flufenamic Acid Affects Multiple Currents and Causes Intracellular Ca2+ Release in Aplysia Bag Cell Neurons

2008 ◽  
Vol 100 (1) ◽  
pp. 38-49 ◽  
Author(s):  
Kate E. Gardam ◽  
Julia E. Geiger ◽  
Charlene M. Hickey ◽  
Anne Y. Hung ◽  
Neil S. Magoski
Keyword(s):  
Channel Blocker ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
Cell Voltage ◽  
Cation Channel ◽  
Flufenamic Acid ◽  
Whole Cell ◽  
Positive Shift ◽  
Intracellular Ca ◽  
Bag Cell Neurons

Flufenamic acid (FFA) is a nonsteroidal antiinflammatory agent, commonly used to block nonselective cation channels. We previously reported that FFA potentiated, rather than inhibited, a cation current in Aplysia bag cell neurons. Prompted by this paradoxical result, the present study examined the effects of FFA on membrane currents and intracellular Ca2+ in cultured bag cell neurons. Under whole cell voltage clamp, FFA evoked either outward ( Iout) or inward ( Iin) currents. Iout had a rapid onset, was inhibited by the K+ channel blocker, tetraethylammonium, and was associated with both an increase in membrane conductance and a negative shift in the whole cell current reversal potential. Iin developed more slowly, was inhibited by the cation channel blocker, Gd3+, and was concomitant with both an increased conductance and positive shift in reversal potential. FFA also enhanced the use-dependent inactivation and caused a positive-shift in the activation curve of the voltage-dependent Ca2+ current. Furthermore, as measured by ratiometric imaging, FFA produced a rise in intracellular Ca2+ that persisted in the absence of extracellular Ca2+ and was reduced by depleting either the endoplasmic reticulum and/or mitochondrial stores. Ca2+ appeared to be involved in the activation of Iin, as strong intracellular Ca2+ buffering effectively eliminated Iin but did not alter Iout. Finally, the effects of FFA were likely not due to block of cyclooxygenase given that the general cyclooxygenase inhibitor, indomethacin, failed to evoke either current. That FFA influences a number of neuronal properties needs to be taken into consideration when employing it as a cation channel antagonist.

scholarly journals Altered Na/Ca exchange distribution in ventricular myocytes from failing hearts

2016 ◽  
Vol 310 (2) ◽  
pp. H262-H268 ◽  
Author(s):  
Hanne C. Gadeberg ◽  
Simon M. Bryant ◽  
Andrew F. James ◽  
Clive H. Orchard
Keyword(s):  
Heart Failure ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Coronary Artery Ligation ◽  
Sham Operation ◽  
Ca Current ◽  
Artery Ligation ◽  
Whole Cell ◽  
Rat Hearts ◽  
T Tubules

In mammalian cardiac ventricular myocytes, Ca efflux via Na/Ca exchange (NCX) occurs predominantly at T tubules. Heart failure is associated with disrupted t-tubular structure, but its effect on t-tubular function is less clear. We therefore investigated t-tubular NCX activity in ventricular myocytes isolated from rat hearts ∼18 wk after coronary artery ligation (CAL) or corresponding sham operation (Sham). NCX current ( INCX) and l-type Ca current ( ICa) were recorded using the whole cell, voltage-clamp technique in intact and detubulated (DT) myocytes; intracellular free Ca concentration ([Ca]i) was monitored simultaneously using fluo-4. INCX was activated and measured during application of caffeine to release Ca from sarcoplasmic reticulum (SR). Whole cell INCX was not significantly different in Sham and CAL myocytes and occurred predominantly in the T tubules in Sham myocytes. CAL was associated with redistribution of INCX and ICa away from the T tubules to the cell surface and an increase in t-tubular INCX/ ICa density from 0.12 in Sham to 0.30 in CAL myocytes. The decrease in t-tubular INCX in CAL myocytes was accompanied by an increase in the fraction of Ca sequestered by SR. However, SR Ca content was not significantly different in Sham, Sham DT, and CAL myocytes but was significantly increased by DT of CAL myocytes. In Sham myocytes, there was hysteresis between INCX and [Ca]i, which was absent in DT Sham but present in CAL and DT CAL myocytes. These data suggest altered distribution of NCX in CAL myocytes.

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