scholarly journals Voltage Clamp Studies on the Effect of Internal Cesium Ion on Sodium and Potassium Currents in the Squid Giant Axon

1966 ◽  
Vol 50 (2) ◽  
pp. 279-293 ◽  
Author(s):  
William J. Adelman ◽  
Joseph P. Senft
Keyword(s):  
Sea Water ◽  
Sodium Current ◽  
Severe Depression ◽  
Outward Current ◽  
Giant Axon ◽  
Resting Potential ◽  
Negative Slope ◽  
Potential Range ◽  
Sodium Currents ◽  
Cesium Ion

Isolated and cleaned giant axons of Loligo pealii were internally perfused with solutions containing cesium sulfate and potassium fluoride. Membrane currents obtained as a function of clamped membrane potentials indicated a severe depression of the delayed outward current component normally attributed to potassium ion movement. Steady-state currents showed a negative slope in the potential range from -45 to -5 mv which corresponded to the negative slope for the peak sodium current relation vs. membrane potential which suggested long duration sodium currents. Using sodium-free sea water externally, sodium currents were separated from total currents and these persisted for longer times than normal. This result suggested that internal cesium, ion delays the sodium conductance turnoff. The separated nonsodium currents showed an abnormal rectification as compared with those predicted by the independence principle, such that while potassium permeability appeared normal at the resting potential, its value decreased progressively with increasing depolarization.

scholarly journals Membrane Potentials of the Lobster Giant Axon Obtained by Use of the Sucrose-Gap Technique

1962 ◽  
Vol 45 (6) ◽  
pp. 1195-1216 ◽  
Author(s):  
Fred J. Julian ◽  
John W. Moore ◽  
David E. Goldman
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Sea Water ◽  
Sucrose Solution ◽  
Chloride Concentration ◽  
Giant Axon ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Gap Technique ◽  
Sucrose Gap

A method similar to the sucrose-gap technique introduced be Stäpfli is described for measuring membrane potential and current in singly lobster giant axons (diameter about 100 micra). The isotonic sucrose solution used to perfuse the gaps raises the external leakage resistance so that the recorded potential is only about 5 per cent less than the actual membrane potential. However, the resting potential of an axon in the sucrose-gap arrangement is increased 20 to 60 mv over that recorded by a conventional micropipette electrode when the entire axon is bathed in sea water. A complete explanation for this effect has not been discovered. The relation between resting potential and external potassium and sodium ion concentrations shows that potassium carries most of the current in a depolarized axon in the sucrose-gap arrangement, but that near the resting potential other ions make significant contributions. Lowering the external chloride concentration decreases the resting potential. Varying the concentration of the sucrose solution has little effect. A study of the impedance changes associated with the action potential shows that the membrane resistance decreases to a minimum at the peak of the spike and returns to near its initial value before repolarization is complete (a normal lobster giant axon action potential does not have an undershoot). Action potentials recorded simultaneously by the sucrose-gap technique and by micropipette electrodes are practically superposable.

Mechanisms of depolarizing inhibition at the crayfish giant motor synapse. II. Quantitative reconstruction

1990 ◽  
Vol 64 (2) ◽  
pp. 541-550 ◽  
Author(s):  
D. H. Edwards
Keyword(s):  
Potassium Current ◽  
Sodium Current ◽  
Outward Current ◽  
Resting Potential ◽  
Excitatory Postsynaptic Potential ◽  
Inhibitory Effects ◽  
Inward Current ◽  
Postsynaptic Potential ◽  
Parameter Values ◽  
Outward Potassium Current

1. The relative strengths of four mechanisms of depolarizing synaptic inhibition described in the previous paper were evaluated with an electrical model of the giant motor synapse (GMS) and postsynaptic region of the motor giant motoneuron (MoG). 2. The model consists of one compartment that represents the presynaptic region of the medial giant (MG) interneuron and three compartments that represent the postsynaptic region and proximal axon of the MoG. The presynaptic MG compartment is linked to a postsynaptic MoG compartment by a rectifying conductance that represents the GMS. Each compartment consists of parallel paths to ground for active and/or passive membrane currents. 3. Parameter values of the model were set so the MG compartment would replicate an MG impulse and the MoG compartments would replicate the current-clamp, voltage-clamp, and synaptic responses of a single MoG neuron described in the previous paper. The Hodgkin-Huxley equations described voltage-sensitive sodium and potassium currents. 4. Comparison of the MoG compartment currents that mediate an inhibited excitatory postsynaptic potential (EPSP) [triggered during a depolarizing inhibitory postsynaptic potential (d-IPSP)] with those of an uninhibited EPSP indicate that all four mechanisms have significant inhibitory effects. Reverse bias of the GMS by the d-IPSP reduced the GMS current by 65 nA (12%). The remaining inward current was further reduced by a 243-nA outward current through the inhibitory postsynaptic conductance. The d-IPSP inactivated sodium conductance so the inward sodium current evoked by the EPSP was reduced by 319 nA (-68%). The d-IPSP reduced the latency for potassium activation by the EPSP so that the outward potassium current coincided with the inward sodium current and reduced the net inward current by 100 nA. Together, these mechanisms reduced the EPSP amplitude by 69%. 5. The resting potential of MoG is normally 15 mV more positive than MG rest potential, but in some preparations this difference may be as much as 25 mV or as little as 0 mV. Corresponding differences in the rest potentials of the MoG and MG models have little effect on the amplitude of the model MoG EPSP because changes in the inward synaptic and sodium currents are balanced by corresponding changes in the outward potassium current.

scholarly journals Action of External Divalent Ion Reduction on Sodium Movement in the Squid Giant Axon

1961 ◽  
Vol 45 (1) ◽  
pp. 93-103 ◽  
Author(s):  
William J. Adelman ◽  
John W. Moore
Keyword(s):  
Sea Water ◽  
Giant Axon ◽  
Sodium Concentration ◽  
Squid Giant Axon ◽  
Ion Concentration ◽  
Resting Potential ◽  
Slow Increase ◽  
Sodium Permeability ◽  
Sodium Accumulation ◽  
Sodium Flux

Voltage clamp measurements of the sodium potential have been made on the resting squid giant axon to study the effect of variations in external divalent ion concentration upon net sodium flux. From these measurements the intracellular sodium concentration and the net sodium inflow were calculated using the Nernst relation and constant activity coefficients. While an axon bathed in artificial sea water shows a slow increase in internal sodium concentration, the rate of sodium accumulation is increased about two times by reducing external calcium and magnesium concentrations to 0.1 times their normal values. The mean inward net sodium flux increases from a mean control value of 97 pmole/cm2 sec. to 186 pmole/cm2 sec. in low divalent solution. Associated with these effects of external divalent ion reduction are a marked decrease in action potential amplitude, little or no change in resting potential, and a shift along the voltage axis of the curve relating peak sodium conductance to membrane potential similar to that obtained by Frankenhaeuser and Hodgkin (1957). These results implicate divalent ions in long term (minutes to hours) sodium permeability.

Electrophysiological properties of rainbow trout cardiac myocytes in serum-free primary culture

2002 ◽  
Vol 282 (4) ◽  
pp. R1200-R1209 ◽  
Author(s):  
Antti Nurmi ◽  
Matti Vornanen
Keyword(s):  
Primary Culture ◽  
Cardiac Myocytes ◽  
Ventricular Myocytes ◽  
Sodium Current ◽  
Outward Current ◽  
Culture Conditions ◽  
Resting Potential ◽  
Delayed Rectifier ◽  
Altered Expression ◽  
Serum Free

A low-density primary culture of trout ventricular myocytes in serum-free growth medium was established and maintained for up to 10 days at 17°C. The myocytes retained their normal rod shaped morphology, capacitive surface area of the sarcolemma (SL), and contractile quiescence. However, sarcolemmal cation currents changed significantly, some permanently, some transiently, after 8–10 days of culture. TTX-sensitive sodium current ( I Na) and Ba2+-sensitive background inward rectifier potassium current ( I K1) were permanently depressed to 24–28% of their control density measured in freshly isolated myocytes. In contrast, L-type calcium current ( I Ca) was only transiently downregulated; after 2–3 days in culture, the density of the current was 32% of the control and recovered to the control value after 8–10 days in culture. The changes in membrane currents were reflected in the shape of the action potential (AP). After 2–3 days in culture, maximal overshoot potential and resting potential were significantly reduced, and the durations of the AP at 50 and 90% repolarization were significantly increased. These changes became significantly more pronounced after 8–10 days of culture, with the exception of AP duration at 50% repolarization level. The shortening of the early plateau phase may reflect an additional change to an outward current, presumably the rapid component of the delayed rectifier ( I Kr). Although the present findings indicate that fish cardiac myocytes can be maintained in serum-free primary culture for at least 10 days at 17°C, some but not all of the electrophysiological characteristics of the myocytes change markedly during culture. The changes in ion currents were not due to loss of sarcolemmal membrane and therefore are likely to represent altered expression of cation currents as an adaptive response to culture conditions.

scholarly journals Persistent Currents and Discharge Patterns in Rat Hindlimb Motoneurons

2010 ◽  
Vol 104 (3) ◽  
pp. 1566-1577 ◽  
Author(s):  
Thomas M. Hamm ◽  
Vladimir V. Turkin ◽  
Neha K. Bandekar ◽  
Derek O'Neill ◽  
Ranu Jung
Keyword(s):  
Outward Current ◽  
Resting Potential ◽  
Negative Slope ◽  
Leak Current ◽  
Persistent Currents ◽  
Outward Currents ◽  
Inward Currents ◽  
Input Conductance ◽  
Discharge Patterns ◽  
Relative Change

We report here the first direct measurements of persistent inward currents (PICs) in rat hindlimb motoneurons, obtained from ketamine–xylazine anesthetized rats during slow voltage ramps performed by single-electrode somatic voltage clamp. Most motoneurons expressed PICs and current–voltage ( I– V) relations often contained a negative-slope region (NSR; 13/19 cells). PICs activated at −52.7 ± 3.89 mV, 9 mV negative to spike threshold. NSR onset was −44.2 ± 4.1 mV. PIC amplitudes were assessed by maximum inward currents measured relative to extrapolated leak current and to NSR-onset current. PIC conductance at potentials just positive to activation was assessed by the relative change in slope conductance ( gin/ gleak). PIC amplitudes varied widely; some exceeded 5 and 10 nA relative to current at NSR onset or leak current, respectively. PIC amplitudes did not vary significantly with input conductance, but PIC amplitudes normalized by recruitment current decreased with increasing input conductance. Similarly, gin/ gleak decreased with increasing input conductance. Currents near resting potential on descending limbs of I– V relations were often outward, relative to ascending-limb currents. This residual outward current was correlated with increases in leak conductance on the descending limb and with input conductance. Excluding responses with accommodation, residual outward currents matched differences between recruitment and derecruitment currents, suggesting a role for residual outward current in frequency adaptation. Comparison of potentials for PIC activation and NSR onset with interspike trajectories during discharge demonstrated correspondence between PIC activation and frequency–current ( f– I) range boundaries. Contributions of persistent inward and outward currents to motoneuron discharge characteristics are discussed.

scholarly journals The sodium current underlying action potentials in guinea pig hippocampal CA1 neurons.

1988 ◽  
Vol 91 (3) ◽  
pp. 373-398 ◽  
Author(s):  
P Sah ◽  
A J Gibb ◽  
P W Gage
Keyword(s):  
Action Potentials ◽  
Time Course ◽  
Sodium Current ◽  
Hippocampal Slices ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Sodium Currents ◽  
Time To Peak ◽  
Ca1 Region ◽  
Inward Currents

Neurons were acutely dissociated from the CA1 region of hippocampal slices from guinea pigs. Whole-cell recording techniques were used to record and control membrane potential. When the electrode contained KF, the average resting potential was about -40 mV and action potentials in cells at -80 mV (current-clamped) had an amplitude greater than 100 mV. Cells were voltage-clamped at 22-24 degrees C with electrodes containing CsF. Inward currents generated with depolarizing voltage pulses reversed close to the sodium equilibrium potential and could be completely blocked with tetrodotoxin (1 microM). The amplitude of these sodium currents was maximal at about -20 mV and the amplitude of the tail currents was linear with potential, which indicates that the channels were ohmic. The sodium conductance increased with depolarization in a range from -60 to 0 mV with an average half-maximum at about -40 mV. The decay of the currents was not exponential at potentials more positive than -20 mV. The time to peak and half-decay time of the currents varied with potential and temperature. Half of the channels were inactivated at a potential of -75 mV and inactivation was essentially complete at -40 to -30 mV. Recovery from inactivation was not exponential and the rate varied with potential. At lower temperatures, the amplitude of sodium currents decreased, their time course became longer, and half-maximal inactivation shifted to more negative potentials. In a small fraction of cells studied, sodium currents were much more rapid but the voltage dependence of activation and inactivation was very similar.

scholarly journals EFFECTS OF EXTERNAL IONS ON MEMBRANE POTENTIALS OF A LOBSTER GIANT AXON

1958 ◽  
Vol 41 (3) ◽  
pp. 529-542 ◽  
Author(s):  
John C. Dalton
Keyword(s):  
Action Potential ◽  
Sea Water ◽  
Giant Axon ◽  
Membrane Potentials ◽  
Squid Giant Axon ◽  
Resting Potential ◽  
Magnesium Concentration ◽  
Constant Field ◽  
Order Of Magnitude ◽  
External Calcium

The effects of varying external concentrations of normally occurring cations on membrane potentials in the lobster giant axon have been studied and compared with data presently available from the squid giant axon. A decrease in the external concentration of sodium ions causes a reversible reduction in the amplitude of the action potential and its rate of rise. No effect on the resting potential was detected. The changes are of the same order of magnitude, but greater than would be predicted for an ideal sodium electrode. Increase in external potassium causes a decrease in resting potential, and a decrease in potassium causes an increase in potential. The data so obtained are similar to those which have been reported for the squid giant axon, and cannot be exactly fitted to the Goldman constant field equation. Lowering external calcium below 25 mM causes a reduction in resting and action potentials, and the occasional occurrence of repetitive activity. The decrease in action potential is not solely attributable to a decrease in resting potential. Increase of external calcium from 25 to 50 mM causes no change in transmembrane potentials. Variations of external magnesium concentration between zero and 50 mM had no measurable effect on membrane potentials. These studies on membrane potentials do not indicate a clear choice between the use of sea water and Cole's perfusion solution as the better external medium for studies on lobster nerve.

scholarly journals Current-Voltage Relations in the Lobster Giant Axon Membrane Under Voltage Clamp Conditions

1962 ◽  
Vol 45 (6) ◽  
pp. 1217-1238 ◽  
Author(s):  
Fred J. Julian ◽  
John W. Moore ◽  
David E. Goldman
Keyword(s):  
Steady State ◽  
Voltage Clamp ◽  
Sea Water ◽  
Outward Current ◽  
Giant Axon ◽  
Squid Axon ◽  
Initial Current ◽  
Axon Membrane ◽  
Current Voltage ◽  
Steady State Current

The sucrose-gap method introduced by Stämpfli provides a means for the application of a voltage clamp to the lobster giant axon, which responds to a variety of different experimental procedures in ways quite similar to those reported for the squid axon and frog node. This is particularly true for the behavior of the peak initial current. However, the steady state current shows some differences. It has a variable slope conductance less than that of the peak initial current. The magnitude of the steady state slope conductance is related to the length of the repolarization phase of the action potential, which does not have an undershoot in the lobster. The steady state outward current is maintained for as long as 100 msec.; this is in contrast to a decline of about 50 per cent in the squid axon. Lowering the external calcium concentration produces shifts in the current-voltage relations qualitatively similar to those obtained from the squid axon. On the basis of the data available, there is no reason to doubt that the Hodgkin and Huxley analysis for the squid giant axon in sea water can be applied to the lobster giant axon.

scholarly journals Resting and Action Potentials of the Squid Giant Axon in Vivo

1960 ◽  
Vol 43 (5) ◽  
pp. 961-970 ◽  
Author(s):  
John W. Moore ◽  
Kenneth S. Cole
Keyword(s):  
Sea Water ◽  
Giant Axon ◽  
Blood Oxygenation ◽  
Resting Potential ◽  
Liquid Junction ◽  
Axon Membrane ◽  
Nernst Potential ◽  
Initial Action ◽  
Calculated Liquid

Blood oxygenation and circulation were maintained in Loligo pealii for several hours by a strong flow of sea water over both gills on the open, flat mantle. Potentials were measured with a 3 M KCl-filled glass microelectrode penetrating the giant axon membrane. An hour or more after the mantle was opened, the potentials were similar to those observed in excised axons and in preparations without circulation; spike height 100 mv.; undershoot 12 mv., decaying at 6 v./sec.; resting potential 63 mv. However, the earliest (20 minute) resting potentials were up to 70 mv. and 73 mv. Occasional initial action potential measurements (40 to 50 minute) showed a decay of the undershoot that was less than one-tenth the rate observed later. This suggests that in even better preparations there would be no decay, thereby increasing the resting potential and spike height by 12 mv. With the calculated liquid junction potential of 4 mv. the absolute resting potential in the "normal" axon in vivo is estimated to be about 77 mv., which is close to the Nernst potential for the potassium ratio between squid blood and axoplasm. The differences between such a normal axon and the usual isolated axon can be accounted for by a negligible leakage conductance in the normal axon.

scholarly journals Slow sodium inactivation in nerve after exposure to sulhydryl blocking reagents.

1977 ◽  
Vol 69 (2) ◽  
pp. 183-202 ◽  
Author(s):  
P Shrager
Keyword(s):  
Sodium Current ◽  
Potassium Conductance ◽  
Kinetic Studies ◽  
High Specificity ◽  
Resting Potential ◽  
Dependent Manner ◽  
Sodium Currents ◽  
Time To Peak ◽  
Sodium Inactivation ◽  
Protein Sulfhydryl Groups

Exposure to N-ethylmaleimide (NEM), a reagent that binds covalently to protein sulfhydryl groups, results in a specific reduction in sodium conductance in crayfish axons. Resting potential, the delayed rise in potassium conductance, and the selectivity of the sodium channel are unaffected. Sodium currents are only slightly increased by hyperpolarizing prepulses of up to 50 ms duration, but can be restored to about 70% of their value before treatment if this duration is increased to 300-800 ms. The time to peak sodium current and the time constant of decay of sodium tail currents are unaffected by NEM, suggesting that the sodium activation system remains unaltered. Kinetic studies suggest that NEM reacts with a "slow" sodium inactivation system that is present in normal axons and that may be seen after depolarization produced by lowered the holding potential or increasing the external potassium concentration. NEM also perturbs the fast h inactivation system, and in a potential-dependent manner. At small depolarizations tauh is decreased, while at strong depolarizations it is increased over control values. Experiments with structural analogs of NEM suggest that sulfhydryl block is involved, but do not rule out an action similar to that of local anesthetics, p-Chloromercuriphenylsulfonic acid (PCMBS), another reagent with high specificity for SH groups, also blocks sodium currents, but restoration with prolonged hyperpolarizations is not possible.

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