Determination of Pure Voltage-Dependent Ca2+ Current in Paramecium Caudatum and its Inhibition by Divalent Cations

1985 ◽  
Vol 119 (1) ◽  
pp. 321-334
Author(s):  
FRANK WEHNER ◽  
EILO HILDEBRAND
Keyword(s):  
Dissociation Constants ◽  
Divalent Cations ◽  
Equilibrium Potential ◽  
Ca Channel ◽  
Paramecium Caudatum ◽  
Voltage Range ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents

Voltage-dependent Ca2+ currents in Paramecium caudatum were studied under voltage clamp conditions. To separate Ca2+ inward currents from concomitant K+ outward currents, the voltage-dependent Ca2+ conductance was temporarily inactivated by a preceding depolarization. The remaining currents were then subtracted from the overall currents measured in the absence of a prepulse. In this way pure Ca2+ currents could be obtained up to a depolarization of 100 mV, which is about 50 mV below the theoretical Ca2+ equilibrium potential (Eca). Ca2+ currents were maximal at a depolarization of 35 mV and declined with further approach to Eca, but they did not reverse sign in the voltage range tested. In the presence of Mg2+, Co2+, Mn2+ or Ni2+, the Ca2+ inward currents decreased to a different extent. From experiments where these cations were added at different concentrations and from measurements at different Ca2+ concentrations in the absence of other divalent cations the following ratio of apparent dissociation constants could be derived: kNi: kco: kca: kMg = 1:3:4.3-4.7:5:6.5. With a confidence of 95% the absolute value of kca lies between 40 and 130μmol l−1. These results indicate that Ca2+ and other divalent cations compete for binding sites at the Ca-channel and thus determine excitability. Indirect effects due to changes of the surface potential are discussed.

scholarly journals Permeation and Gating in CaV3.1 (α1G) T-type Calcium Channels Effects of Ca2+, Ba2+, Mg2+, and Na+

2008 ◽  
Vol 132 (2) ◽  
pp. 223-238 ◽  
Author(s):  
Nilofar Khan ◽  
I. Patrick Gray ◽  
Carlos A. Obejero-Paz ◽  
Stephen W. Jones
Keyword(s):  
Calcium Channels ◽  
Surface Charge ◽  
Concentration Dependence ◽  
Divalent Cations ◽  
Hek 293 ◽  
Voltage Range ◽  
293 Cells ◽  
Instantaneous Current ◽  
Voltage Dependent ◽  
Inward Currents

We examined the concentration dependence of currents through CaV3.1 T-type calcium channels, varying Ca2+ and Ba2+ over a wide concentration range (100 nM to 110 mM) while recording whole-cell currents over a wide voltage range from channels stably expressed in HEK 293 cells. To isolate effects on permeation, instantaneous current–voltage relationships (IIV) were obtained following strong, brief depolarizations to activate channels with minimal inactivation. Reversal potentials were described by PCa/PNa = 87 and PCa/PBa = 2, based on Goldman-Hodgkin-Katz theory. However, analysis of chord conductances found that apparent Kd values were similar for Ca2+ and Ba2+, both for block of currents carried by Na+ (3 μM for Ca2+ vs. 4 μM for Ba2+, at −30 mV; weaker at more positive or negative voltages) and for permeation (3.3 mM for Ca2+ vs. 2.5 mM for Ba2+; nearly voltage independent). Block by 3–10 μM Ca2+ was time dependent, described by bimolecular kinetics with binding at ∼3 × 108 M−1s−1 and voltage-dependent exit. Ca2+o, Ba2+o, and Mg2+o also affected channel gating, primarily by shifting channel activation, consistent with screening a surface charge of 1 e− per 98 Å2 from Gouy-Chapman theory. Additionally, inward currents inactivated ∼35% faster in Ba2+o (vs. Ca2+o or Na+o). The accelerated inactivation in Ba2+o correlated with the transition from Na+ to Ba2+ permeation, suggesting that Ba2+o speeds inactivation by occupying the pore. We conclude that the selectivity of the “surface charge” among divalent cations differs between calcium channel families, implying that the surface charge is channel specific. Voltage strongly affects the concentration dependence of block, but not of permeation, for Ca2+ or Ba2+.

scholarly journals Effect of FMRFamide on voltage-dependent currents in identified centrifugal neurons of the optic lobe of the cuttlefish, Sepia officinalis

2020 ◽  
Author(s):  
Abdesslam Chrachri
Keyword(s):  
Visual Processing ◽  
Calcium Current ◽  
Optic Lobe ◽  
Low Voltage ◽  
Sodium Current ◽  
Calcium Currents ◽  
Delayed Rectifier ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents

AbstractWhole-cell patch-clamp recordings from identified centrifugal neurons of the optic lobe in a slice preparation allowed the characterization of five voltage-dependent currents; two outward and three inward currents. The outward currents were; the 4-aminopyridine-sensitive transient potassium or A-current (IA), the TEA-sensitive sustained current or delayed rectifier (IK). The inward currents were; the tetrodotoxin-sensitive transient current or sodium current (INa). The second is the cobalt- and cadmium-sensitive sustained current which is enhanced by barium and blocked by the dihydropyridine antagonist, nifedipine suggesting that it could be the L-type calcium current (ICaL). Finally, another transient inward current, also carried by calcium, but unlike the L-type, this current is activated at more negative potentials and resembles the low-voltage-activated or T-type calcium current (ICaT) of other preparations.Application of the neuropeptide FMRFamide caused a significant attenuation to the peak amplitude of both sodium and sustained calcium currents without any apparent effect on the transient calcium current. Furthermore, FMRFamide also caused a reduction of both outward currents in these centrifugal neurons. The fact that FMRFamide reduced the magnitude of four of five characterized currents could suggest that this neuropeptide may act as a strong inhibitory agent on these neurons.SummaryFMRFamide modulate the ionic currents in identified centrifugal neurons in the optic lobe of cuttlefish: thus, FMRFamide could play a key role in visual processing of these animals.

Segment-specific effects of FMRFamide on membrane properties of heart interneurons in the leech

1995 ◽  
Vol 74 (4) ◽  
pp. 1485-1497 ◽  
Author(s):  
J. Schmidt ◽  
S. Gramoll ◽  
R. L. Calabrese
Keyword(s):  
Outward Current ◽  
Membrane Conductance ◽  
Membrane Properties ◽  
Inward Current ◽  
Specific Effects ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
Conductance Increase

1. The effects of Phe-Met-Arg-Phe (FMRF)amide (10(-6) M) on membrane properties of heart interneurons in the third, fourth, and fifth segmental ganglia [HN(3), HN(4), and HN(5) cells, respectively] of the leech were studied using discontinuous current-clamp and single-electrode voltage-clamp techniques. FMRFamide was focally applied onto the soma of the cell under investigation. 2. Application of FMRFamide depolarized HN(3) and HN(4) cells by evoking an inward current. These responses were subject to pronounced desensitization. The inward currents evoked by application of FMRFamide were associated with an increase in membrane conductance and appeared to be voltage dependent. Currents were enhanced at more depolarized potentials. 3. The responsiveness of the HN(3) and HN(4) cells was not affected when the Ca2+ concentration in the bath saline was reduced from normal (1.8 mM) to 0.1 mM. The depolarizing response on application of FMRFamide was blocked when Co2+ was substituted for Ca2+. 4. HN(3) and HN(4) cells did not respond to FMRFamide application in Na(+)-free solution. Inward currents were largely reduced when bath saline with 30% of the normal Na+ concentration was used. When Li+ was substituted for Na+ in the saline, application of FMRFamide still evoked depolarizing responses in HN(3) and HN(4) cells. 5. We conclude that focal application of FMRFamide onto the somata of HN(3) and HN(4) cells evokes a voltage-dependent inward current, carried largely by Na+. 6. Focal application of FMRFamide onto somata of HN(5) cells hyperpolarized these cells by activating a voltage-dependent outward current. 7. HN(5) cells were loaded with Cl- until inhibitory postsynaptic potentials carried by Cl- reversed. Cl(-)-loaded cells still responded with a hyperpolarization when FMRFamide was applied onto their somata. Therefore the outward current evoked by FMRFamide appears to be mediated by a K+ conductance increase. 8. Application of FMRFamide onto the somata of HN(5) cells enhanced outward currents that were evoked by depolarizing voltage steps from a holding potential of -45 mV. 9. We conclude that the hyperpolarizing response of HN(5) cells to focal application of FMRFamide onto their somata is the result of an up-regulation of a voltage-dependent K+ current.

scholarly journals Voltage-dependent conductances in Limulus ventral photoreceptors.

1982 ◽  
Vol 79 (2) ◽  
pp. 187-209 ◽  
Author(s):  
J E Lisman ◽  
G L Fain ◽  
P M O'Day
Keyword(s):  
Outward Current ◽  
Delayed Rectifier ◽  
Molluscan Neurons ◽  
Inward Current ◽  
Transient Component ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
A Current

The voltage-dependent conductances of Limulus ventral photoreceptors have been investigated using a voltage-clamp technique. Depolarization in the dark induces inward and outward currents. The inward current is reduced by removing Na+ or Ca2+ and is abolished by removing both ions. These results suggest that both Na+ and Ca2+ carry voltage-dependent inward current. Inward current is insensitive to tetrodotoxin but is blocked by external Ni2+. The outward current has a large transient component that is followed by a smaller maintained component. Intracellular tetraethylammonium preferentially reduces the maintained component, and extracellular 4-amino pyridine preferentially reduces the transient component. Neither component is strongly affected by removal of extracellular Ca2+ or by intracellular injection of EGTA. It is concluded that the photoreceptors contain at least three separate voltage-dependent conductances: 1) a conductance giving rise to inward currents; 2) a delayed rectifier giving rise to maintained outward K+ current; and 3) a rapidly inactivating K+ conductance similar to the A current of molluscan neurons.

scholarly journals Inactivation of calcium channel current in the calf cardiac Purkinje fiber. Evidence for voltage- and calcium-mediated mechanisms.

1984 ◽  
Vol 84 (5) ◽  
pp. 705-726 ◽  
Author(s):  
R S Kass ◽  
M C Sanguinetti
Keyword(s):  
Charge Carrier ◽  
Divalent Cations ◽  
Purkinje Fiber ◽  
Ca Channel ◽  
Channel Current ◽  
Zero Current ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
Ca Channel Current ◽  
Dependent Mechanism

We have studied the influence of divalent cations on Ca channel current in the calf cardiac Purkinje fiber to determine whether this current inactivates by voltage- or Ca-mediated mechanisms, or by a combination of the two. We measured the reversal (or zero current) potential of the current when Ba, Sr, or Ca were the permeant divalent cations and determined that depletion of charge carrier does not account for time-dependent relaxation of Ca channel current in these preparations. Inactivation of Ca channel current persists when Ba or Sr replaces Ca as the permeant divalent cation, but the voltage dependence of the rate of inactivation is markedly changed. This effect cannot be explained by changes in external surface charge. Instead, we interpret the results as evidence that inactivation is both voltage and Ca dependent. Inactivation of Sr or Ba currents reflects a voltage-dependent process. When Ca is the divalent charge carrier, an additional effect is observed: the rate of inactivation is increased as Ca enters during depolarizing pulses, perhaps because of an additional Ca-dependent mechanism.

scholarly journals Voltage-dependent and odorant-regulated currents in isolated olfactory receptor neurons of the channel catfish.

1992 ◽  
Vol 99 (4) ◽  
pp. 505-529 ◽  
Author(s):  
T Miyamoto ◽  
D Restrepo ◽  
J H Teeter
Keyword(s):  
Action Potentials ◽  
Olfactory Receptor Neurons ◽  
Olfactory Neurons ◽  
Outward Currents ◽  
Na Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
Receptor Neurons ◽  
K Currents

The electrical properties of olfactory receptor neurons, enzymatically dissociated from the channel catfish (Ictalurus punctatus), were studied using the whole-cell patch-clamp technique. Six voltage-dependent ionic currents were isolated. Transient inward currents (0.1-1.7 nA) were observed in response to depolarizing voltage steps from a holding potential of -80 mV in all neurons examined. They activated between -70 and -50 mV and were blocked by addition of 1 microM tetrodotoxin (TTX) to the bath or by replacing Na+ in the bath with N-methyl-D-glucamine and were classified as Na+ currents. Sustained inward currents, observed in most neurons examined when Na+ inward currents were blocked with TTX and outward currents were blocked by replacing K+ in the pipette solution with Cs+ and by addition of 10 mM Ba2+ to the bath, activated between -40 and -30 mV, reached a peak at 0 mV, and were blocked by 5 microM nimodipine. These currents were classified as L-type Ca2+ currents. Large, slowly activating outward currents that were blocked by simultaneous replacement of K+ in the pipette with Cs+ and addition of Ba2+ to the bath were observed in all olfactory neurons examined. The outward K+ currents activated over approximately the same range as the Na+ currents (-60 to -50 mV), but the Na+ currents were larger at the normal resting potential of the neurons (-45 +/- 11 mV, mean +/- SD, n = 52). Four different types of K+ currents could be differentiated: a Ca(2+)-activated K+ current, a transient K+ current, a delayed rectifier K+ current, and an inward rectifier K+ current. Spontaneous action potentials of varying amplitude were sometimes observed in the cell-attached recording configuration. Action potentials were not observed in whole-cell recordings with normal internal solution (K+ = 100 mM) in the pipette, but frequently appeared when K+ was reduced to 85 mM. These observations suggest that the membrane potential and action potential amplitude of catfish olfactory neurons are significantly affected by the activity of single channels due to the high input resistance (6.6 +/- 5.2 G omega, n = 20) and low membrane capacitance (2.1 +/- 1.1 pF, n = 46) of the cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Currents in the presynaptic terminal arbors of barnacle photoreceptors

1993 ◽  
Vol 10 (2) ◽  
pp. 261-270 ◽  
Author(s):  
Jon H. Hayashi ◽  
Ann E. Stuart
Keyword(s):  
Outward Current ◽  
Presynaptic Terminal ◽  
Resting Potential ◽  
Previous Evidence ◽  
Outward Currents ◽  
Dependent Inactivation ◽  
Postsynaptic Cell ◽  
Tetraethylammonium Ion ◽  
Voltage Dependent ◽  
Inward Currents

AbstractWe have described the currents flowing across the presynaptic membranes of the four median photoreceptors of the giant barnacle, Balanus nubilus, using a quasi-voltage clamp arrangement. Membrane potential, measured in the terminal region of one photoreceptor, was controlled in all four terminals by feedback current supplied through the nerve containing the photoreceptors’ axons. The [Ca2+] ∘ in the saline was reduced to decrease the Ca2+ current, enabling better voltage control, and tetraethylammonium ion (TEA, 20 mM) was added to block a fast voltage-dependent K+ conductance.Depolarizing voltage steps from the resting potential in the dark (−60 mV) evoked slow, inward Ca2+-dependent currents which could be blocked by Co2+, Mg2+, or Cd2+. The Ca2+ currents were followed by large outward currents that persisted for many seconds after the offset of moderate or large pulses. These tail currents increased in magnitude and duration with pulse duration and reversed at about −80 mV, consistent with previous evidence for a Ca2+-activated K+ conductance in this membrane. When the Ca2+-activated outward current was reduced to zero by increasing the [K+]∘ so as to set EK at −20 mV, and then stepping the voltage to this value, the step evoked a steady inward Ca2+ current. Thus, the Ca2+ current did not show voltage- or Ca2+-dependent inactivation. When Ba2+ was substituted for Ca2+, 500-ms depolarizing steps evoked steady inward currents but no outward currents. In any given experiment, the activation voltage of the Ca2+ or Ba2+ current did not depend on holding potential.At the barnacle photoreceptor’s synapse, the postsynaptic cell adapts to maintained presynaptic voltage by a mechanism that is not understood. We conclude that neither Ca2+ current inactivation nor a shift in activation voltage with holding potential can account for this adaptation.

scholarly journals Effects of barium on the potassium conductance of squid axon.

1980 ◽  
Vol 75 (6) ◽  
pp. 727-750 ◽  
Author(s):  
D C Eaton ◽  
M S Brodwick
Keyword(s):  
Rate Constants ◽  
Dissociation Constants ◽  
Divalent Cations ◽  
Potassium Conductance ◽  
Competitive Inhibitor ◽  
Squid Axon ◽  
Voltage Dependent ◽  
Different Temperatures ◽  
Nanomolar Range ◽  
External K

Ba++ ion blocks K+ conductance at concentrations in the nanomolar range. This blockage is time and voltage dependent. From the time dependence it is possible to determine the forward and reverse rate constants for what appears to be an essentially first-order process of Ba++ interaction. The voltage dependence of the rate constants and the dissociation constants place the site of interaction near the middle of the membrane field. Comparison of the efficacy of Ba++ block at various internal K+ concentrations suggests that Ba++ is probably a simple competitive inhibitor of K+ interaction with the K+ conductance. The character of Ba++ block in high external K+ solutions suggests that Ba++ ion may be "knocked-off" the site by inward movement of external K+. Examination of the effects of other divalent cations suggests that the channel may have a closed state with a divalent cation inside the channel. The relative blockage at different temperatures implies a strong interaction between Ba++ and the K+ conductance.

scholarly journals Effects of Divalent Cations on Outward Potassium Currents in Leech Retzius Nerve Cells

2016 ◽  
Vol 17 (4) ◽  
pp. 309-314
Author(s):  
Zorica Jovanovic ◽  
Olgica Mihaljevic ◽  
Irena Kostic
Keyword(s):  
Action Potential ◽  
Neuronal Excitability ◽  
Divalent Cations ◽  
Extracellular Fluid ◽  
Outward Current ◽  
Potassium Currents ◽  
Nerve Cells ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Retzius Cells

Abstract The present study examines the effects of divalent metals, cadmium (Cd2+) and manganese (Mn2+), on the outward potassium currents of Retzius cells in the hirudinid leeches Haemopis sanguisuga using conventional two-microelectrode voltageclamp techniques. The outward potassium current is activated by depolarization and plays an important role in determining both the neuronal excitability and action potential duration. A strong inhibition of the fast current and a clear reduction in the late currents of the outward current with 1 mM Cd2+ were obtained, which indicated that both components are sensitive to this metal. Complete blockage of the fast and partial reduction of the slow outward currents was observed after adding 1 mM Mn2+ to the extracellular fluid. These data show that the outward K+ current in leech Retzius nerve cells comprises at least two components: a voltage-dependent K+ current and a Ca2+- activated K+ current. These observations also indicate that Cd2+ is more eff ective than Mn2+ in blocking ion fl ow through these channels and that suppressing Ca2+-activated K+ outward currents can prolong the action potential in nerve cells.

scholarly journals Large-Conductance Calcium-Activated Potassium Channels and Voltage-Dependent Sodium Channels in Human Cementoblasts

2021 ◽  
Vol 12 ◽  
Author(s):  
Satomi Kamata ◽  
Maki Kimura ◽  
Sadao Ohyama ◽  
Shuichiro Yamashita ◽  
Yoshiyuki Shibukawa
Keyword(s):  
Alveolar Bone ◽  
Attachment Site ◽  
Ionic Currents ◽  
Ionic Channels ◽  
Patch Clamp Recording ◽  
Physiological Processes ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents

Cementum, which is excreted by cementoblasts, provides an attachment site for collagen fibers that connect to the alveolar bone and fix the teeth into the alveolar sockets. Transmembrane ionic signaling, associated with ionic transporters, regulate various physiological processes in a wide variety of cells. However, the properties of the signals generated by plasma membrane ionic channels in cementoblasts have not yet been described in detail. We investigated the biophysical and pharmacological properties of ion channels expressed in human cementoblast (HCEM) cell lines by measuring ionic currents using conventional whole-cell patch-clamp recording. The application of depolarizing voltage steps in 10 mV increments from a holding potential (Vh) of −70 mV evoked outwardly rectifying currents at positive potentials. When intracellular K+ was substituted with an equimolar concentration of Cs+, the outward currents almost disappeared. Using tail current analysis, the contributions of both K+ and background Na+ permeabilities were estimated for the outward currents. Extracellular application of tetraethylammonium chloride (TEA) and iberiotoxin (IbTX) reduced the densities of the outward currents significantly and reversibly, whereas apamin and TRAM-34 had no effect. When the Vh was changed to −100 mV, we observed voltage-dependent inward currents in 30% of the recorded cells. These results suggest that HCEM express TEA- and IbTX-sensitive large-conductance Ca2+-activated K+ channels and voltage-dependent Na+ channels.

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