Activity-Dependent Initiation of a Prolonged Depolarization in Aplysia Bag Cell Neurons: Role for a Cation Channel

2007 ◽  
Vol 97 (3) ◽  
pp. 2465-2479 ◽  
Author(s):  
Anne Y. Hung ◽  
Neil S. Magoski
Keyword(s):  
Pulse Duration ◽  
Action Potentials ◽  
Reversal Potential ◽  
Egg Laying ◽  
Cation Channel ◽  
Flufenamic Acid ◽  
Depolarization Current ◽  
Calmodulin Kinase ◽  
Current Voltage ◽  
Bag Cell Neurons

The translation of prior activity into changes in excitability is essential for memory and the initiation of behavior. After brief synaptic input, the bag cell neurons of Aplysia californica undergo a nearly 30-min afterdischarge to release egg-laying hormone. The present study examines a prolonged depolarization in cultured bag cell neurons. A 5-Hz, 10-s action potential train elicited a depolarization of about 10 mV, which lasted ≤30 min and was reduced by calmodulin kinase inhibition. Very broad action potentials (resulting from TEA application) decreased prolonged depolarization amplitude, indicating that strong Ca2+ influx did not necessarily promote the response. The prolonged depolarization current ( IPD) was recorded after 5-Hz, 10-s trains of square voltage pulses of varying duration (10–150 ms). Despite Ca2+ influx increasing steadily with pulse duration, IPD was most reliably initiated at 100 ms, suggesting a Ca2+ window or limit exists for triggering IPD. Consistent with this, modestly broader action potentials, evoked by lengthening the train current-pulse duration, resulted in smaller prolonged depolarizations. With respect to the properties of IPD, it displayed a linear current–voltage relationship with a reversal potential of about −45 mV that was shifted to approximately −25 mV by lowering internal K+ or about −56 mV by lowering external Na+ and Ca2+. IPD was blocked by Gd3+, but was not antagonized by MDL-123302A, SKF-96365, 2-APB, tetrodotoxin, or flufenamic acid. Optimal Ca2+ influx may activate calmodulin kinase and a voltage-independent, nonselective cation channel to initiate the prolonged depolarization, thereby contributing to the afterdischarge and reproduction.

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.

Regulation of Cation Channel Voltage and Ca2+ Dependence by Multiple Modulators

2009 ◽  
Vol 102 (1) ◽  
pp. 259-271 ◽  
Author(s):  
Kate E. Gardam ◽  
Neil S. Magoski
Keyword(s):  
Neuronal Excitability ◽  
Voltage Dependence ◽  
Hormone Secretion ◽  
Egg Laying ◽  
Cation Channel ◽  
Ion Channel Regulation ◽  
Kinase C ◽  
The Right ◽  
Bag Cell Neurons ◽  
Inside Out

Ion channel regulation is key to controlling neuronal excitability. However, the extent that modulators and gating factors interact to regulate channels is less clear. For Aplysia, a nonselective cation channel plays an essential role in reproduction by driving an afterdischarge in the bag cell neurons to elicit egg-laying hormone secretion. We examined the regulation of cation channel voltage and Ca2+ dependence by protein kinase C (PKC) and inositol trisphosphate (IP3)—two prominent afterdischarge signals. In excised, inside-out patches, the channel remained open longer and reopened more often with depolarization from −90 to +30 mV. As previously reported, PKC could closely associate with the channel and increase activity at −60 mV. We now show that, following the effects of PKC, voltage dependence was shifted to the left (essentially enhanced), particularly at more negative voltages. Conversely, the voltage dependence of channels lacking PKC was shifted to the right (essentially suppressed). Predictably, activity was increased at all Ca2+ concentrations following the effects of PKC; nevertheless, Ca2+ dependence was actually shifted to the right. Moreover, whereas IP3 did not alter activity at −60 mV, it drastically shifted Ca2+ dependence to the right—an outcome largely reversed by PKC. With respect to the afterdischarge, these data suggest PKC initially upregulates the channel by direct gating and shifting voltage dependence to the left. Subsequently, PKC and IP3 attenuate the channel by suppressing Ca2+ dependence. This ensures hormone delivery by allowing afterdischarge initiation and maintenance but also prevents interminable bursting. Similar regulatory interactions may be used by other neurons to achieve diverse outputs.

Mechanism of long-lasting synaptic inhibition in Aplysia neuron R15

1980 ◽  
Vol 44 (6) ◽  
pp. 1148-1160 ◽  
Author(s):  
W. B. Adams ◽  
I. Parnas ◽  
I. B. Levitan
Keyword(s):  
Action Potentials ◽  
Potassium Conductance ◽  
Reversal Potential ◽  
Short Exposure ◽  
Ion Conductance ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Aplysia Neuron ◽  
Reversible Component ◽  
Stimulation Of

1. Long-lasting inhibition is a synaptically mediated response found in certain molluscan nerve cells that fire action potentials in bursts. It is elicited by repetitive stimulation of a presynaptic nerve and may last for minutes or hours after stimulation. 2. Voltage-clamp techniques were employed to measure the voltage dependence of the synaptically elicited current. Current-voltage curves were obtained by stepping or sweeping the voltage over the range -40 to -120 mV. 3. Long-lasting inhibition was found to be mediated by two separate conductance mechanisms. A component that reverses near -80 mV is most prominent at times up to 5 min following stimulation. A component with no reversal potential between -40 and -120 mV predominates at later times. 4. The reversible component is attenuated by reducing the intensity of stimulation of the presynaptic nerve, by injection of TEA into the postsynaptic cell, or by activation of a potassium conductance with serotonin prior to stimulation of the nerve. Thus, the reversible component appears to be mediated by an increase in potassium conductance. 5. The effects of the nonreversible component measured in the soma appear to be too large to attribute it to a conductance change that is electrically "distant" from the soma. It is attenuated by turning off a resting inward ion conductance with dopamine prior to stimulation of the nerve. It is not affected by short exposure to ouabain, but is attenuated by longer exposures that reduce the sodium and calcium gradients. Thus, the nonreversible component may be mediated by a decrease in voltage-dependent inward current flow carried by sodium or calcium.

The peptide FMRFa terminates a discharge in Aplysia bag cell neurons by modulating calcium, potassium, and chloride conductances

1993 ◽  
Vol 69 (6) ◽  
pp. 2164-2173 ◽  
Author(s):  
T. Fisher ◽  
C. H. Lin ◽  
L. K. Kaczmarek
Keyword(s):  
Electrical Stimulation ◽  
Action Potentials ◽  
Close Contact ◽  
Reversal Potential ◽  
Outward Current ◽  
Chloride Ions ◽  
Resting Potential ◽  
Inhibitory Influence ◽  
Channel Blockers ◽  
Bag Cell Neurons

1. Electrical stimulation of an afferent nerve triggers a 30-min period of firing of action potentials in the bag cell neurons of Aplysia californica. This afterdischarge causes the animal to undergo a long-lasting sequence of stereotyped reproductive behaviors culminating in laying of eggs. The connective sheath surrounding the clusters of bag cell neurons is interspersed with a network of particles that are immunoreactive to an antiserum raised against the tetrapeptide neurotransmitter Phe-Met-Arg-Phe-amide (FMRFa). Because the sheath is known to be rich in processes from the bag cell neurons, these data suggest that an FMRFa-like peptide may be located in neuronal processes that are in close contact with those of the bag cell neurons. 2. Application of FMRFa to bag cell neurons in intact abdominal ganglia effectively suppresses the onset of the afterdischarge in response to electrical stimulation and terminates an ongoing afterdischarge in a reversible manner. 3. Application of FMRFa to isolated bag cell neurons in primary cell culture causes an attenuation of the amplitude of evoked action potentials. This could be attributed in part to an attenuation of the voltage-activated calcium current, which in voltage-clamp experiments was found to be reduced by 10-40%. 4. Application of FMRFa to bag cell neuron in primary culture also causes a hyperpolarization of the membrane potential by activating an outward current with a reversal potential of approximately -67 mV. Ion substitution experiments, together with application of channel blockers, indicate that this current is carried by both potassium and chloride ions. Activation of this current is suppressed by treatment of the cells with either a cyclic AMP analogue or a phorbol ester activator of protein kinase C. 5. FMRFa exerts a powerful inhibitory influence on the bag cell neurons by altering the properties of ion currents involved in both the generation of action potentials and control of the resting potential. This suggests that this neuropeptide plays a role in the regulation of the onset of afterdischarge in vivo.

Ca2+ entry through a non-selective cation channel in Aplysia bag cell neurons

Neuroscience ◽  
2009 ◽  
Vol 162 (4) ◽  
pp. 1023-1038 ◽  
Author(s):  
J.E. Geiger ◽  
C.M. Hickey ◽  
N.S. Magoski
Keyword(s):  
Cation Channel ◽  
Bag Cell Neurons

Calcium-dependent potassium conductance in rat supraoptic nucleus neurosecretory neurons

1985 ◽  
Vol 54 (6) ◽  
pp. 1375-1382 ◽  
Author(s):  
C. W. Bourque ◽  
J. C. Randle ◽  
L. P. Renaud
Keyword(s):  
Time Constant ◽  
Action Potentials ◽  
Supraoptic Nucleus ◽  
Potassium Conductance ◽  
Reversal Potential ◽  
Input Resistance ◽  
Mean Amplitude ◽  
Progressive Increase ◽  
Calcium Dependent ◽  
Neurosecretory Neurons

Intracellular recordings of rat supraoptic nucleus neurons were obtained from perfused hypothalamic explants. Individual action potentials were followed by hyperpolarizing afterpotentials (HAPs) having a mean amplitude of -7.4 +/- 0.8 mV (SD). The decay of the HAP was approximated by a single exponential function having a mean time constant of 17.5 +/- 6.1 ms. This considerably exceeded the cell time constant of the same neurons (9.5 +/- 0.8 ms), thus indicating that the ionic conductance underlying the HAP persisted briefly after each spike. The HAP had a reversal potential of -85 mV and was unaffected by intracellular Cl- ionophoresis of during exposure to elevated extracellular concentrations of Mg2+. In contrast, the peak amplitude of the HAP was proportional to the extracellular Ca2+ concentration and could be reversibly eliminated by replacing Ca2+ with Co2+, Mn2+, or EGTA in the perfusion fluid. During depolarizing current pulses, evoked action potential trains demonstrated a progressive increase in interspike intervals associated with a potentiation of successive HAPs. This spike frequency adaptation was reversibly abolished by replacing Ca2+ with Co2+, Mn2+, or EGTA. Bursts of action potentials were followed by a more prolonged afterhyperpolarization (AHP) whose magnitude was proportional to the number of impulses elicited (greater than 20 Hz) during a burst. Current injection revealed that the AHP was associated with a 20-60% decrease in input resistance and showed little voltage dependence in the range of -70 to -120 mV. The reversal potential of the AHP shifted with the extracellular concentration of K+ [( K+]o) with a mean slope of -50 mV/log[K+]o.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Activation of Slo2.1 channels by niflumic acid

2010 ◽  
Vol 135 (3) ◽  
pp. 275-295 ◽  
Author(s):  
Li Dai ◽  
Vivek Garg ◽  
Michael C. Sanguinetti
Keyword(s):  
Voltage Dependence ◽  
Reversal Potential ◽  
Niflumic Acid ◽  
Flufenamic Acid ◽  
Channel Activation ◽  
Outward Currents ◽  
Transmembrane Voltage ◽  
High K ◽  
Charged Residues ◽  
K Current

Slo2.1 channels conduct an outwardly rectifying K+ current when activated by high [Na+]i. Here, we show that gating of these channels can also be activated by fenamates such as niflumic acid (NFA), even in the absence of intracellular Na+. In Xenopus oocytes injected with <10 ng cRNA, heterologously expressed human Slo2.1 current was negligible, but rapidly activated by extracellular application of NFA (EC50 = 2.1 mM) or flufenamic acid (EC50 = 1.4 mM). Slo2.1 channels activated by 1 mM NFA exhibited weak voltage dependence. In high [K+]e, the conductance–voltage (G-V) relationship had a V1/2 of +95 mV and an effective valence, z, of 0.48 e. Higher concentrations of NFA shifted V1/2 to more negative potentials (EC50 = 2.1 mM) and increased the minimum value of G/Gmax (EC50 = 2.4 mM); at 6 mM NFA, Slo2.1 channel activation was voltage independent. In contrast, V1/2 of the G-V relationship was shifted to more positive potentials when [K+]e was elevated from 1 to 300 mM (EC50 = 21.2 mM). The slope conductance measured at the reversal potential exhibited the same [K+]e dependency (EC50 = 23.5 mM). Conductance was also [Na+]e dependent. Outward currents were reduced when Na+ was replaced with choline or mannitol, but unaffected by substitution with Rb+ or Li+. Neutralization of charged residues in the S1–S4 domains did not appreciably alter the voltage dependence of Slo2.1 activation. Thus, the weak voltage dependence of Slo2.1 channel activation is independent of charged residues in the S1–S4 segments. In contrast, mutation of R190 located in the adjacent S4–S5 linker to a neutral (Ala or Gln) or acidic (Glu) residue induced constitutive channel activity that was reduced by high [K+]e. Collectively, these findings indicate that Slo2.1 channel gating is modulated by [K+]e and [Na+]e, and that NFA uncouples channel activation from its modulation by transmembrane voltage and intracellular Na+.

Lysophosphatidic acid, serum, and hyposmolarity activate Cl- currents in corneal keratocytes

1995 ◽  
Vol 269 (6) ◽  
pp. C1385-C1393 ◽  
Author(s):  
M. A. Watsky
Keyword(s):  
Lysophosphatidic Acid ◽  
Reversal Potential ◽  
Flufenamic Acid ◽  
Disulfonic Acid ◽  
Hypotonic Stress ◽  
Outward Currents ◽  
Fetal Bovine ◽  
Patch Technique ◽  
Corneal Keratocytes ◽  
In Cells

The influence of serum, lysophosphatidic acid (LPA), and hyposmotic stress on the ion channel activity of normal and cryo-injured rabbit corneal keratocytes was investigated. Whole cell currents were examined using the amphotericin perforated-patch technique. In cells from wounded corneas, fetal bovine serum activated large, holding voltage-insensitive, fast-activating, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-, flufenamic acid-, and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB)-blockable outward currents showing inactivation at depolarized voltages. LPA activated identical currents, also only in cells from wounded corneas. Blocker and reversal potential experiments characterized the current as a Cl- currents (Icl). Lysophosphatidylcholine (10 microM) failed to activate the current. An identical current was activated by hyposmotic stimulation in cells from control and wounded corneas. Hyposmotic stimulation also activated Icl in cells from wounded corneas that were unresponsive to LPA. We conclude that serum, LPA, and hypotonic stress activate Icl in keratocytes from wounded corneas. We also conclude that LPA is a serum factor that can activate Icl and that hyposmotic activation may work through a signaling pathway separate from that of LPA.

scholarly journals Action Potentials in Rhodnius Oocytes: Repolarization is Sensitive to Potassium Channel Blockers

1986 ◽  
Vol 126 (1) ◽  
pp. 119-132
Author(s):  
M. J. O'DONNELL
Keyword(s):  
Potassium Channel ◽  
Action Potentials ◽  
Potassium Conductance ◽  
Channel Blockers ◽  
Calcium Dependent ◽  
Outward Rectification ◽  
Current Voltage ◽  
Potassium Channel Blockers ◽  
Potassium Conductances ◽  
Voltage Dependent

Depolarization of Rhodnius oocytes evokes action potentials (APs) whose rising phase is calcium-dependent. The ionic basis for the repolarizing (i.e. falling) phase of the AP was examined. Addition of potassium channel blockers (tetraethylammonium, tetrabutylammonium, 4-aminopyridine, atropine) to the bathing saline increased the duration and overshoot of APs. Intracellular injection of tetraethyl ammonium had similar effects. These results suggest that a voltage-dependent potassium conductance normally contributes to repolarization. Repolarization does not require a chloride influx, because substitution of impermeant anions for chloride did not increase AP duration. AP duration and overshoot actually decreased progressively when chloride levels were reduced. Current/voltage curves show inward and outward rectification, properties often associated with potassium conductances. Outward rectification was largely blocked by external tetraethylammonium. Possible functions of the rectifying properties of the oocyte membrane are discussed.

Hodgkin–Huxley neurons with defective and blocked ion channels

2015 ◽  
Vol 26 (10) ◽  
pp. 1550112 ◽  
Author(s):  
James Christopher S. Pang ◽  
Johnrob Y. Bantang
Keyword(s):  
Ion Channels ◽  
Action Potentials ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
Potassium Ions ◽  
Temporal Response ◽  
Constant Input ◽  
Control Drug ◽  
Channel Control ◽  
Sodium And Potassium

We utilize the original Hodgkin–Huxley (HH) model to consider the effects of defective ion channels to the temporal response of neurons. Statistics of firing rate and inter-spike interval (ISI) reveal that production of action potentials (APs) in neurons is not sensitive to changes in membrane conductance for sodium and potassium ions, as well as to the reversal potential for sodium ions, as long as the relevant parameters do not exceed 13% from their normal levels. We also found that blockage of a critical fraction of either sodium or potassium channels (dependent on constant input current) respectively limits the firing activity or increases spontaneous spiking activity of neurons. Our model may be used to guide experiment designs related to ion channel control drug development.

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