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.

scholarly journals Ca2+-induced uncoupling of Aplysia bag cell neurons

2015 ◽  
Vol 113 (3) ◽  
pp. 808-821 ◽  
Author(s):  
Zahra Dargaei ◽  
Dominic Standage ◽  
Christopher J. Groten ◽  
Gunnar Blohm ◽  
Neil S. Magoski
Keyword(s):  
Time Course ◽  
Electrical Coupling ◽  
Egg Laying ◽  
Neuroendocrine Cells ◽  
Electrical Synapse ◽  
Electrical Transmission ◽  
Synchronous Firing ◽  
Cell Recording ◽  
Intracellular Ca ◽  
Bag Cell Neurons

Electrical transmission is a dynamically regulated form of communication and key to synchronizing neuronal activity. The bag cell neurons of Aplysia are a group of electrically coupled neuroendocrine cells that initiate ovulation by secreting egg-laying hormone during a prolonged period of synchronous firing called the afterdischarge. Accompanying the afterdischarge is an increase in intracellular Ca2+ and the activation of protein kinase C (PKC). We used whole cell recording from paired cultured bag cell neurons to demonstrate that electrical coupling is regulated by both Ca2+ and PKC. Elevating Ca2+ with a train of voltage steps, mimicking the onset of the afterdischarge, decreased junctional current for up to 30 min. Inhibition was most effective when Ca2+ entry occurred in both neurons. Depletion of Ca2+ from the mitochondria, but not the endoplasmic reticulum, also attenuated the electrical synapse. Buffering Ca2+ with high intracellular EGTA or inhibiting calmodulin kinase prevented uncoupling. Furthermore, activating PKC produced a small but clear decrease in junctional current, while triggering both Ca2+ influx and PKC inhibited the electrical synapse to a greater extent than Ca2+ alone. Finally, the amplitude and time course of the postsynaptic electrotonic response were attenuated after Ca2+ influx. A mathematical model of electrically connected neurons showed that excessive coupling reduced recruitment of the cells to fire, whereas less coupling led to spiking of essentially all neurons. Thus a decrease in electrical synapses could promote the afterdischarge by ensuring prompt recovery of electrotonic potentials or making the neurons more responsive to current spreading through the network.

Chloride and cation currents activated by bradykinin in coronary venular endothelial cells

1994 ◽  
Vol 267 (6) ◽  
pp. H2508-H2515
Author(s):  
J. Song ◽  
M. J. Davis
Keyword(s):  
Endothelial Cells ◽  
Time Course ◽  
Reversal Potential ◽  
Disulfonic Acid ◽  
Equilibrium Potential ◽  
K Channel ◽  
Inward Current ◽  
Cation Current ◽  
Inward Currents ◽  
K Current

Bradykinin (BK) is known to activate several types of ion channels in endothelial cells, including a K+ channel and a nonselective cation channel. The predominant BK-activated current in most endothelial cells appears to be an outward, Ca(2+)-activated K+ current. We consistently recorded a rapidly activated, spontaneously inactivated inward current stimulated by BK in bovine coronary venular endothelial cells (CVECs). With the use of a whole cell, perforated patch recording mode, the average magnitude of the current was -293 +/- 38 pA. Simultaneous measurements of current and intracellular Ca2+ concentration ([Ca2+]i) showed that the inward current correlated closely with transient increases in [Ca2+]i due to Ca2+ release from intracellular stores. The current could be blocked by 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid (DIDS) but not by La3+, and it persisted in Ca(2+)-free/Na(+)-free solution. When intra- and/or extracellular Cl- concentrations were altered, the reversal potential of the current shifted according to the calculated Cl- -equilibrium potential, indicating that the current was carried primarily by Cl-. Another inward current was also activated by BK. This current was slower to activate, could be blocked by La3+, but was not blocked by DIDS. The time course of the slowly activated current correlated with the plateau phase of the BK-stimulated [Ca2+]i increase, which was similar to the behavior of a nonselective cation current reported previously. We propose that these two currents may contribute to the depolarizations and net inward currents induced by BK in this cell line.

Ca2+-Induced Ca2+ Release in Aplysia Bag Cell Neurons Requires Interaction Between Mitochondrial and Endoplasmic Reticulum Stores

2008 ◽  
Vol 100 (1) ◽  
pp. 24-37 ◽  
Author(s):  
Julia E. Geiger ◽  
Neil S. Magoski
Keyword(s):  
Endoplasmic Reticulum ◽  
Cyclopiazonic Acid ◽  
Neuroendocrine Cells ◽  
Action Potential Firing ◽  
Simultaneous Imaging ◽  
Carbonyl Cyanide ◽  
Potential Firing ◽  
Intracellular Ca ◽  
Bag Cell Neurons ◽  
Protein Kinase C Activation

Intracellular Ca2+ is influenced by both Ca2+ influx and release. We examined intracellular Ca2+ following action potential firing in the bag cell neurons of Aplysia californica. Following brief synaptic input, these neuroendocrine cells undergo an afterdischarge, resulting in elevated Ca2+ and the secretion of neuropeptides to initiate reproduction. Cultured bag cell neurons were injected with the Ca2+ indicator, fura-PE3, and subjected to simultaneous imaging and electrophysiology. Delivery of a 5-Hz, 1-min train of action potentials (mimicking the fast phase of the afterdischarge) produced a Ca2+ rise that markedly outlasted the initial influx, consistent with Ca2+-induced Ca2+ release (CICR). This response was attenuated by about half with ryanodine or depletion of the endoplasmic reticulum (ER) by cyclopiazonic acid. However, depletion of the mitochondria, with carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone, essentially eliminated CICR. Dual depletion of the ER and mitochondria did not reduce CICR further than depletion of the mitochondria alone. Moreover, tetraphenylphosphonium, a blocker of mitochondrial Ca2+ release, largely prevented CICR. The Ca2+ elevation during and subsequent to a stimulus mimicking the full afterdischarge was prominent and enhanced by protein kinase C activation. Traditionally, the ER is seen as the primary Ca2+ source for CICR. However, bag cell neuron CICR represents a departure from this view in that it relies on store interaction, where Ca2+ released from the mitochondria may in turn liberate Ca2+ from the ER. This unique form of CICR may be used by both bag cell neurons, and other neurons, to initiate secretion, activate channels, or induce gene expression.

Effects of pinacidil on coronary Ca2+-myosin phosphorylation in cold potassium cardioplegia model

2000 ◽  
Vol 279 (3) ◽  
pp. H882-H888 ◽  
Author(s):  
Naruto Matsuda ◽  
Kathleen G. Morgan ◽  
Frank W. Sellke
Keyword(s):  
Time Course ◽  
Dependent Manner ◽  
Coronary Smooth Muscle ◽  
Intracellular Ca ◽  
No Signaling ◽  
Synthase Inhibitor ◽  
Mlc Phosphorylation ◽  
Dose Dependent ◽  
Cardioplegic Solutions

The effects of the potassium (K+) channel opener pinacidil (Pin) on the coronary smooth muscle Ca2+-myosin light chain (MLC) phosphorylation pathway under hypothermic K+cardioplegia were determined by use of an in vitro microvessel model. Rat coronary arterioles (100–260 μm in diameter) were subjected to 60 min of simulated hypothermic (20°C) K+cardioplegic solutions (K+= 25 mM). We first characterized the time course of changes in intracellular Ca2+concentration, MLC phosphorylation, and diameter and observed that the K+cardioplegia-related vasoconstriction was associated with an activation of the Ca2+-MLC phosphorylation pathway. Supplementation with Pin effectively suppressed the Ca2+accumulation and MLC phosphorylation in a dose-dependent manner and subsequently maintained a small decrease in vasomotor tone. The ATP-sensitive K+(KATP)-channel blocker glibenclamide, but not the nitric oxide (NO) synthase inhibitor Nω-nitro-l-arginine methyl ester, significantly inhibited the effect of Pin. K+cardioplegia augments the coronary Ca2+-MLC pathway and results in vasoconstriction. Pin effectively prevents the activation of this pathway and maintains adequate vasorelaxation during K+cardioplegia through a KATP-channel mechanism not coupled with the endothelium-derived NO signaling cascade.

scholarly journals Redox-assisted regulation of Ca2+ homeostasis in the endoplasmic reticulum by disulfide reductase ERdj5

2016 ◽  
Vol 113 (41) ◽  
pp. E6055-E6063 ◽  
Author(s):  
Ryo Ushioda ◽  
Akitoshi Miyamoto ◽  
Michio Inoue ◽  
Satoshi Watanabe ◽  
Masaki Okumura ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Disulfide Bond ◽  
Plasma Membranes ◽  
Dependent Manner ◽  
Cellular Functions ◽  
Endoplasmic Reticulum Calcium ◽  
Disulfide Reductase ◽  
Intracellular Ca ◽  
Activity Dependent ◽  
Er Calcium

Calcium ion (Ca2+) is an important second messenger that regulates numerous cellular functions. Intracellular Ca2+ concentration ([Ca2+]i) is strictly controlled by Ca2+ channels and pumps on the endoplasmic reticulum (ER) and plasma membranes. The ER calcium pump, sarco/endoplasmic reticulum calcium ATPase (SERCA), imports Ca2+ from the cytosol into the ER in an ATPase activity-dependent manner. The activity of SERCA2b, the ubiquitous isoform of SERCA, is negatively regulated by disulfide bond formation between two luminal cysteines. Here, we show that ERdj5, a mammalian ER disulfide reductase, which we reported to be involved in the ER-associated degradation of misfolded proteins, activates the pump function of SERCA2b by reducing its luminal disulfide bond. Notably, ERdj5 activated SERCA2b at a lower ER luminal [Ca2+] ([Ca2+]ER), whereas a higher [Ca2+]ER induced ERdj5 to form oligomers that were no longer able to interact with the pump, suggesting [Ca2+]ER-dependent regulation. Binding Ig protein, an ER-resident molecular chaperone, exerted a regulatory role in the oligomerization by binding to the J domain of ERdj5. These results identify ERdj5 as one of the master regulators of ER calcium homeostasis and thus shed light on the importance of cross talk among redox, Ca2+, and protein homeostasis in the ER.

Calcium Signals in Nerve Cells

Physiology ◽  
1991 ◽  
Vol 6 (1) ◽  
pp. 6-10 ◽  
Author(s):  
PG Kostyuk ◽  
AV Tepikin
Keyword(s):  
Endoplasmic Reticulum ◽  
Ion Channels ◽  
Nerve Cell ◽  
Second Messengers ◽  
Cell Activity ◽  
Nerve Cells ◽  
Calcium Signals ◽  
Intracellular Ca ◽  
Ca Ions

Increases in intracellular Ca ions follow each cycle of nerve cell activity. Sources of Ca are voltage- and receptor-operated membrane ion channels and endoplasmic reticulum (ER). Ca release from ER can be triggered by different second messengers, and uptake into the ER can terminate the Ca signal.

A Novel Ca2+ Influx Pathway in Mammalian Primary Sensory Neurons Is Activated by Caffeine

2001 ◽  
Vol 86 (1) ◽  
pp. 190-196 ◽  
Author(s):  
Robert E. Hoesch ◽  
Daniel Weinreich ◽  
Joseph P. Y. Kao
Keyword(s):  
Sensory Neurons ◽  
Ryanodine Receptors ◽  
Reversal Potential ◽  
Significant Rise ◽  
Adult Rabbit ◽  
Pharmacological Agents ◽  
Inward Current ◽  
Whole Cell Patch Clamp ◽  
Intracellular Ca ◽  
Ganglion Neurons

Single-cell microfluorimetry and electrophysiology techniques were used to identify and characterize a novel Ca2+ influx pathway in adult rabbit vagal sensory neurons. Acutely dissociated nodose ganglion neurons (NGNs) exhibit robust Ca2+-induced Ca2+ release (CICR) that can be triggered by 10 mM caffeine, the classic agonist of CICR. A caffeine-induced increase in cytosolic-free Ca2+ concentration ([Ca2+]i) is considered diagnostic evidence of the existence of CICR. However, when CICR was disabled through depletion of intracellular Ca2+stores or pharmacological blockade of intracellular Ca2+ release channels (ryanodine receptors), caffeine still elicited a significant rise in [Ca2+]i in ∼50% of NGNs. The same response was not elicited by pharmacological agents that elevate cyclic nucleotide concentrations. Moreover, extracellular Ca2+ was obligatory for such caffeine-induced [Ca2+]i rises in this population of NGNs, suggesting that Ca2+ influx is responsible for this rise. Simultaneous microfluorimetry with whole cell patch-clamp studies showed that caffeine activates an inward current that temporally parallels the rise in [Ca2+]i. The inward current had a reversal potential of +8.1 ± 6.1 (SE) mV ( n = 4), a mean peak amplitude of −126 ± 24 pA ( n = 4) at E m = −50 mV, and a slope conductance of 1.43 ± 0.79 nS ( n= 4). Estimated EC50 values for caffeine-induced CICR and for caffeine-activated current were 1.5 and ∼0.6 mM, respectively. These results indicate that caffeine-induced rises in [Ca2+]i, in the presence of extracellular Ca2+, can no longer be interpreted as unequivocal diagnostic evidence for CICR in neurons. These results also indicate that sensory neurons possess a novel Ca2+ influx pathway.

scholarly journals Effectiveness in Block by Dexmedetomidine of Hyperpolarization-Activated Cation Current, Independent of Its Agonistic Effect on α2-Adrenergic Receptors

2020 ◽  
Vol 21 (23) ◽  
pp. 9110
Author(s):  
Te-Ling Lu ◽  
Te-Jung Lu ◽  
Sheng-Nan Wu
Keyword(s):  
Adrenergic Receptors ◽  
Time Course ◽  
Ionic Currents ◽  
Inhibitory Effect ◽  
Firing Frequency ◽  
Neuroendocrine Cells ◽  
Gh3 Cells ◽  
Membrane Excitability ◽  
Cation Current

Dexmedetomidine (DEX), a highly selective agonist of α2-adrenergic receptors, has been tailored for sedation without risk of respiratory depression. Our hypothesis is that DEX produces any direct perturbations on ionic currents (e.g., hyperpolarization-activated cation current, Ih). In this study, addition of DEX to pituitary GH3 cells caused a time- and concentration-dependent reduction in the amplitude of Ih with an IC50 value of 1.21 μM and a KD value of 1.97 μM. A hyperpolarizing shift in the activation curve of Ih by 10 mV was observed in the presence of DEX. The voltage-dependent hysteresis of Ih elicited by long-lasting triangular ramp pulse was also dose-dependently reduced during its presence. In continued presence of DEX (1 μM), further addition of OXAL (10 μM) or replacement with high K+ could reverse DEX-mediated inhibition of Ih, while subsequent addition of yohimbine (10 μM) did not attenuate the inhibitory effect on Ih amplitude. The addition of 3 μM DEX mildly suppressed the amplitude of erg-mediated K+ current. Under current-clamp potential recordings, the exposure to DEX could diminish the firing frequency of spontaneous action potentials. In pheochromocytoma PC12 cells, DEX was effective at suppressing Ih together with a slowing in activation time course of the current. Taken together, findings from this study strongly suggest that during cell exposure to DEX used at clinically relevant concentrations, the DEX-mediated block of Ih appears to be direct and would particularly be one of the ionic mechanisms underlying reduced membrane excitability in the in vivo endocrine or neuroendocrine cells.

5-HT modulation of hyperpolarization-activated inward current and calcium-dependent outward current in a crustacean motor neuron

1992 ◽  
Vol 68 (2) ◽  
pp. 496-508 ◽  
Author(s):  
O. Kiehn ◽  
R. M. Harris-Warrick
Keyword(s):  
Motor Neuron ◽  
Time Course ◽  
Reversal Potential ◽  
Outward Current ◽  
Resting Membrane Potential ◽  
Inward Current ◽  
Calcium Dependent ◽  
Voltage Dependent ◽  
K Concentration ◽  
Conductance Increase

1. Serotonergic modulation of a hyperpolarization-activated inward current, Ih, and a calcium-dependent outward current, Io(Ca), was examined in the dorsal gastric (DG) motor neuron, with the use of intracellular recording techniques in an isolated preparation of the crab stomatogastric ganglion (STG). 2. Hyperpolarization of the membrane from rest with maintained current pulses resulted in a slow time-dependent relaxation back toward rest and a depolarizing overshoot after termination of the current pulse. In voltage clamp, hyperpolarizing commands negative to approximately -70 mV caused a slowly developing inward current, Ih, which showed no inactivation. Repolarization back to the holding potential of -50 mV revealed a slow inward tail current. 3. The reversal potential for Ih was approximately -35 mV. Raising extracellular K+ concentration ([K+]o) from 11 to 22 mM enhanced, whereas decreasing extracellular Na+ concentration ([Na+]o) reduced the amplitude of Ih. These results indicate that Ih in DG is carried by both K+ and Na+ ions. 4. Bath application of serotonin (5-HT; 10 microM) caused a marked increase in the amplitude of Ih through its active voltage ranges. 5. The time course of activation of Ih was well fitted by a single exponential function and strongly voltage dependent. 5-HT increased the rate of activation of Ih. 5-HT also slowed the rate of deactivation of the Ih tail on repolarization to -50 mV. 6. The activation curve for the conductance (Gh) underlying Ih was obtained by analyzing tail currents. 5-HT shifted the half activation for Gh from approximately -105 mV in control to -95 mV, resulting in an increase in the amplitude of Gh active at rest. 7. Two to 4 mM Cs+ abolished Ih, whereas barium (200 microM to 2 mM) had only weak suppressing effects on Ih. Concomitantly, Cs+ also blocked the 5-HT-induced inward current and conductance increase seen at voltages negative to rest. In current clamp, Cs+ caused DG to hyperpolarize 3-4 mV from rest, suggesting that Ih is partially active at rest and contributes to the resting membrane potential. 8. Depolarizing voltage commands from a holding potential of -50 mV resulted in a total outward current (Io) with an initial transient component and a sustained steady-state component. Application of 5-HT reduced both the transient and sustained components of Io. 9. Io was reduced by 10-20 mM tetraethylammonium (TEA), suggesting that it is primarily a K+ current.(ABSTRACT TRUNCATED AT 400 WORDS)

Intracellular calcium plays a role as the second messenger of hypotonic stress in gene regulation of SGK1 and ENaC in renal epithelial A6 cells

2008 ◽  
Vol 294 (1) ◽  
pp. F177-F186 ◽  
Author(s):  
Akiyuki Taruno ◽  
Naomi Niisato ◽  
Yoshinori Marunaka
Keyword(s):  
Early Phase ◽  
Time Course ◽  
Short Circuit ◽  
Second Messenger ◽  
Dependent Manner ◽  
A6 Cells ◽  
Hypotonic Stress ◽  
Intracellular Ca ◽  
Two Phases ◽  
Delayed Phase

In A6 cells, a renal cell line derived from Xenopus laevis, hypotonic stress stimulates the amiloride-sensitive Na+ transport. Hypotonic action on Na+ transport consists of two phases, a nongenomic early phase and a genomic delayed phase. Although it has been reported that, during the genomic phase, hypotonic stress stimulates transcription of Na+ transport-related genes, such as serum- and glucocorticoid-inducible kinase 1 (SGK1) and subunits of the epithelial Na+ channel (ENaC), increasing Na+ transport, the mechanism remains unknown. We focused the present study on the role of intracellular Ca2+ in hypotonicity-induced SGK1 and ENaC subunit transcription. Since hypotonic stress raises intracellular Ca2+ concentration in A6 cells, we hypothesized that Ca2+-dependent signals participate in the genomic action. Using real-time quantitative RT-PCR and Western blot techniques and measuring short-circuit currents, we observed that 1) BAPTA-AM and W7 blunted the hypotonicity-induced expression of SGK1 mRNA and protein, 2) ionomycin dose dependently stimulated expression of SGK1 mRNA and protein under an isotonic condition and the time course of the stimulatory effect of ionomycin on SGK1 mRNA was remarkably similar to that of hypotonic action on SGK1 mRNA, 3) hypotonic stress stimulated transcription of three ENaC subunits in an intracellular Ca2+-dependent manner, and 4) BAPTA-AM retarded the delayed phase of hypotonic stress-induced Na+ transport but had no effect on the early phase. These observations indicate for the first time that intracellular Ca2+ plays a role as the second messenger in hypotonic stress-induced Na+ transport by stimulating transcription of SGK1 and ENaC subunits.

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