Synaptic Current at the Rat Ganglionic Synapse and Its Interactions With the Neuronal Voltage-Dependent Currents

1998 ◽  
Vol 79 (2) ◽  
pp. 727-742 ◽  
Author(s):  
Oscar Sacchi ◽  
Maria Lisa Rossi ◽  
Rita Canella ◽  
Riccardo Fesce
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Time Constant ◽  
Voltage Dependence ◽  
Sympathetic Neurons ◽  
Excitatory Postsynaptic Potential ◽  
Synaptic Current ◽  
Inactivation Curve ◽  
Voltage Dependent ◽  
Steady State Inactivation

Sacchi, Oscar, Maria Lisa Rossi, Rita Canella, and Riccardo Fesce. Synaptic current at the rat ganglionic synapse and its interactions with the neuronal voltage-dependent currents. J. Neurophysiol. 79: 727–742, 1998. The membrane current activated by fast nicotinic excitation of intact and mature rat sympathetic neurons was studied at 37°C, by using the two-microelectrode voltage-clamp technique. The excitatory postsynaptic current (EPSC) was modeled as the difference between two exponentials. A fast time constant (τ2; mean value 0.57 ms), which proves to be virtually voltage-independent, governs the current rise phase and a longer time constant (τ1; range 5.2–6.8 ms in 2 mM Ca2+) describes the current decay and shows a small negative voltage dependence. A mean peak synaptic conductance of 0.58 μS per neuron is measured after activation of the whole presynaptic input in 5 mM Ca2+ external solution (0.40 μS in 2 mM Ca2+). The miniature EPSCs also rise and decay with exponential time constants very similar to those of the compound EPSC recorded at the same voltage. A mean peak conductance of 4.04 nS is estimated for the unitary event. Deconvolution procedures were employed to decompose evoked macrocurrents. It is shown that under appropriate conditions the duration of the driving function describing quantal secretion can be reduced to <1 ms. The shape of the EPSC is accurately mimicked by a complete mathematical model of the sympathetic neuron incorporating the kinetic properties of five different voltage-dependent current types, which were characterized in a previous work. We show that I A channels are opened by depolarizing voltage steps or by synaptic potentials in the subthreshold voltage range, provided that the starting holding voltage is sufficiently negative to remove I A steady-state inactivation (less than −50 mV) and the voltage trajectories are sufficiently large to enter the I A activation range (greater than −65 mV). Under current-clamp conditions, this gives rise to an additional fast component in the early phase of membrane repolarization—in response to voltage pulses—and to a consistent distortion of the excitatory postsynaptic potential (EPSP) time course around its peak—in response to the synaptic signal. When the stimulation initiates an action potential, I A is shown to significantly increase the synaptic threshold conductance (up to a factor of 2 when I A is fully deinactivated), compared with that required when I A is omitted. The voltage dependence of this effect is consistent with the I A steady-state inactivation curve. It is concluded that I A, in addition to speeding up the spike repolarization process, also shunts the excitatory drive and delays or prevents the firing of the neuron action potential.

scholarly journals Voltage-dependent inactivation of slow calcium channels in intact twitch muscle fibers of the frog.

1989 ◽  
Vol 94 (5) ◽  
pp. 937-951 ◽  
Author(s):  
G Cota ◽  
E Stefani
Keyword(s):  
Steady State ◽  
Rate Constant ◽  
Voltage Dependence ◽  
Muscle Fibers ◽  
Dependent Manner ◽  
Inactivation Curve ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Intact Muscle ◽  
Ca2 Channels

Inactivation of slow Ca2+ channels was studied in intact twitch skeletal muscle fibers of the frog by using the three-microelectrode voltage-clamp technique. Hypertonic sucrose solutions were used to abolish contraction. The rate constant of decay of the slow Ca2+ current (ICa) remained practically unchanged when the recording solution containing 10 mM Ca2+ was replaced by a Ca2+-buffered solution (126 mM Ca-maleate). The rate constant of decay of ICa monotonically increased with depolarization although the corresponding time integral of ICa followed a bell-shaped function. The replacement of Ca2+ by Ba2+ did not result in a slowing of the rate of decay of the inward current nor did it reduce the degree of steady-state inactivation. The voltage dependence of the steady-state inactivation curve was steeper in the presence of Ba2+. In two-pulse experiments with large conditioning depolarizations ICa inactivation remained unchanged although Ca2+ influx during the prepulse greatly decreased. Dantrolene (12 microM) increased mechanical threshold at all pulse durations tested, the effect being more prominent for short pulses. Dantrolene did not significantly modify ICa decay and the voltage dependence of inactivation. These results indicate that in intact muscle fibers Ca2+ channels inactivate in a voltage-dependent manner through a mechanism that does not require Ca2+ entry into the cell.

scholarly journals Comparison of excitatory currents activated by different transmitters on crustacean muscle. II. Glutamate-activated currents and comparison with acetylcholine currents present on the same muscle.

1983 ◽  
Vol 81 (4) ◽  
pp. 571-588 ◽  
Author(s):  
C Lingle ◽  
A Auerbach
Keyword(s):  
Steady State ◽  
Time Constant ◽  
Voltage Dependence ◽  
Noise Analysis ◽  
Power Spectra ◽  
Synaptic Current ◽  
Cancer Borealis ◽  
Current Decay ◽  
Marine Crustacean ◽  
Conductance Increase

The properties of glutamate-activated excitatory currents on the gm6 muscle from the foregut of the spiny lobsters Panulirus argus and interruptus and the crab Cancer borealis were examined using either noise analysis, analysis of synaptic current decays, or slow iontophoretic currents. The properties of acetylcholine currents activated in nonjunctional regions of the gm6 muscle were also examined. At 12 degrees C and -80 mV, the predominant time constant of power spectra from glutamate-activated current noise was approximately 7 ms and the elementary conductance was approximately 34 pS. At 12 degrees C and -80 mV, the predominant time constant of acetylcholine-activated channels was approximately 11 ms with a conductance of approximately 12 pS. Focally recorded glutamatergic extracellular synaptic currents on the gm6 muscle decayed with time constants of approximately 7-8 ms at 12 degrees C and -80 mV. The decay time constant was prolonged e-fold about every 225-mV hyperpolarization in membrane potential. The Q10 of the time constant of the synaptic current decay was approximately 2.6. The voltage dependence of the steady-state conductance increase activated by iontophoretic application of glutamate has the opposite direction of the steady-state conductance activated by cholinergic agonists when compared on the gm6 muscles. The glutamate-activated conductance increase is diminished with hyperpolarization. The properties of the marine crustacean glutamate channels are discussed in relation to glutamate channels in other organisms and to the acetylcholine channels found on the gm6 muscle and the gm1 muscle of the decapod foregut (Lingle and Auerbach, 1983).

scholarly journals Inhibition of Kv4.3 by genistein via a tyrosine phosphorylation-independent mechanism

2011 ◽  
Vol 300 (3) ◽  
pp. C567-C575 ◽  
Author(s):  
Hee Jae Kim ◽  
Hye Sook Ahn ◽  
Bok Hee Choi ◽  
Sang June Hahn
Keyword(s):  
Steady State ◽  
Inactivation Kinetics ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Inactivation Curve ◽  
Voltage Range ◽  
Closed State ◽  
Voltage Dependent ◽  
Dependent Inhibition ◽  
Steady State Inactivation

The effects of genistein, a protein tyrosine kinase (PTK) inhibitor, on voltage-dependent K+ (Kv) 4.3 channel were examined using the whole cell patch-clamp techniques. Genistein inhibited Kv4.3 in a reversible, concentration-dependent manner with an IC50 of 124.78 μM. Other PTK inhibitors (tyrphostin 23, tyrphostin 25, lavendustin A) had no effect on genistein-induced inhibition of Kv4.3. Orthovanadate, an inhibitor of protein phosphatases, did not reverse the inhibition of Kv4.3 by genistein. We also tested the effects of two inactive structural analogs: genistin and daidzein. Whereas Kv4.3 was unaffected by genistin, daidzein inhibited Kv4.3, albeit with a lower potency. Genistein did not affect the activation and inactivation kinetics of Kv4.3. Genistein-induced inhibition of Kv4.3 was voltage dependent with a steep increase over the channel opening voltage range. In the full-activation voltage range positive to +20 mV, no voltage-dependent inhibition was found. Genistein had no significant effect on steady-state activation, but shifted the voltage dependence of the steady-state inactivation of Kv4.3 in the hyperpolarizing direction in a concentration-dependent manner. The Ki for the interaction between genistein and the inactivated state of Kv4.3, which was estimated from the concentration-dependent shift in the steady-state inactivation curve, was 1.17 μM. Under control conditions, closed-state inactivation was fitted to a single exponential function, and genistein accelerated closed-state inactivation. Genistein induced a weak use-dependent inhibition. These results suggest that genistein directly inhibits Kv4.3 by interacting with the closed-inactivated state of Kv4.3 channels. This effect is not mediated via inhibition of the PTK activity, because other types of PTK inhibitors could not prevent the inhibitory action of genistein.

Transient and delayed potassium currents in the Retzius cell of the leech, Macrobdella decora

1986 ◽  
Vol 56 (3) ◽  
pp. 812-822 ◽  
Author(s):  
J. Johansen ◽  
A. L. Kleinhaus
Keyword(s):  
Steady State ◽  
Time Constant ◽  
Time Course ◽  
Substantial Part ◽  
Macrobdella Decora ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
K Current ◽  
Retzius Cell ◽  
T Tau

The properties of a quickly inactivating transient K current (IA) and a slowly inactivating delayed K current (IK) were investigated with two-electrode voltage-clamp techniques in the isolated soma of the Retzius cell of the leech, Macrobdella decora. The two currents could be pharmacologically separated according to their different sensitivities to tetraethylammonium ions (TEA) and 4-aminopyridine (4-AP). IA was totally blocked by 3 mM 4-AP but not affected by 25 mM TEA. IK was suppressed almost completely by 25 mM TEA, whereas its peak amplitude only decreased by 10-15% in 3 mM 4-AP. IA was activated at membrane potentials more positive than -35 to -30 mV, whereas the threshold for IK was at more positive potentials of approximately -20 to -15 mV. The activation of IA was rapid with a voltage-dependent time constant [tau m(A)] that varied from 6 to 2 ms for command potentials between -20 and 10 mV (at 22-24 degrees C). The inactivation, which was independent of voltage, was somewhat slower with a time constant (tau A) of approximately 90-110 ms. The time constants for activation [tau m(K)] and the early inactivation phase (tau K) of IK were both voltage dependent. In the range of potential steps from 0 to 30 mV, tau m(K) varied from 12 to 4.5 ms and tau K from 1,500 to 700 ms. The steady-state inactivation of IA varied with holding potential and was complete at potentials more positive than -30 mV. IA was fully available from potentials more negative than -70 mV. IK did not show steady-state inactivation below its threshold of activation. The time course of IA during a maintained depolarization could be reasonably described by the expression IA(t) = IA(infinity) [1-exp(-t/tau m(A))]2 exp(-t/tau A). The time course of activation of IK without allowance for inactivation was approximated by the expression IK(t) = IK(infinity) [1-exp(-t/tau m(K))]2. The reversal potentials and magnitude of both IA and IK were dependent on extra-cellular K concentration, which suggest that a substantial part of the two currents was carried by K ions.

Transient Voltage-Dependent Potassium Currents Are Reduced in NTS Neurons Isolated From Renal Wrap Hypertensive Rats

2005 ◽  
Vol 94 (6) ◽  
pp. 3849-3859 ◽  
Author(s):  
Sergei Belugin ◽  
Steve Mifflin
Keyword(s):  
Steady State ◽  
Voltage Dependence ◽  
Fluorescent Tracer ◽  
Activation Kinetics ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Afferent Inputs ◽  
Made In

Whole cell patch-clamp measurements were made in neurons enzymatically dispersed from the nucleus of the solitary tract (NTS) to determine if alterations occur in voltage-dependent potassium channels from rats made hypertensive (HT) by unilateral nephrectomy/renal wrap for 4 wk. Some rats had the fluorescent tracer DiA applied to the aortic nerve before the experiment to identify NTS neurons receiving monosynaptic baroreceptor afferent inputs. Mean arterial pressure (MAP) was greater in 4-wk HT (165 ± 5 mmHg, n = 26, P < 0.001) rats compared with normotensive (NT) rats (109 ± 3 mmHg measured in 10 of 69 rats). Transient outward currents (TOCs) were observed in 67–82% of NTS neurons from NT and HT rats. At activation voltages from −10 to +10 mV, TOCs were significantly less in HT neurons compared with those observed in NT neurons ( P < 0.001). There were no differences in the voltage-dependent activation kinetics, the voltage dependence of steady-state inactivation, and the rise and decay time constants of the TOCs comparing neurons isolated from NT and HT rats. The 4-aminopyridine–sensitive component of the TOC was significantly less in neurons from HT compared with NT rats ( P < 0.001), whereas steady-state outward currents, whether or not sensitive to 4-aminopyridine or tetraethylammonium, were not different. Delayed excitation, studied under current clamp, was observed in 60–80% of NTS neurons from NT and HT rats and was not different comparing neurons from NT and HT rats. However, examination of the subset of NTS neurons exhibiting somatic DiA fluorescence revealed that DiA-labeled neurons from HT rats had a significantly shorter duration delayed excitation ( n = 8 cells, P = 0.022) than DiA-labeled neurons from NT rats ( n = 7 cells). Neurons with delayed excitation from HT rats had a significantly broader first action potential (AP) and a slower maximal downstroke velocity of repolarization compared with NT neurons with delayed excitation ( P = 0.016 and P = 0.014, respectively). The number of APs in the first 200 ms of a sustained depolarization was greater in HT than NT neurons ( P = 0.012). These results suggest that HT of 4-wk duration reduces TOCs in NTS neurons, and this contributes to reduced delayed excitation and increased AP responses to depolarizing inputs. Such changes could alter baroreflex function in hypertension.

Meperidine and Lidocaine Block of Recombinant Voltage-Dependent Na+Channels 

1999 ◽  
Vol 91 (5) ◽  
pp. 1481-1481 ◽  
Author(s):  
Larry E. Wagner ◽  
Michael Eaton ◽  
Salas S. Sabnis ◽  
Kevin J. Gingrich
Keyword(s):  
Steady State ◽  
Local Anesthesia ◽  
Local Anesthetic ◽  
Voltage Dependence ◽  
Tonic Inhibition ◽  
Na Channel ◽  
Mutant Form ◽  
Na Channels ◽  
Voltage Dependent ◽  
Steady State Inactivation

Background The opioid meperidine induces spinal anesthesia and blocks nerve action potentials, suggesting it is a local anesthetic. However, whether it produces effective clinical local anesthesia in peripheral nerves remains unclear. Classification as a local anesthetic requires clinical local anesthesia but also blockade of voltage-dependent Na+ channels with characteristic features (tonic and phasic blockade and a negative shift in the voltage-dependence of steady-state inactivation) involving an intrapore receptor. The authors tested for these molecular pharmacologic features to explore whether meperidine is a local anesthetic. Methods The authors studied rat skeletal muscle mu1 (RSkM1) voltage-dependent Na+ channels or a mutant form heterologously coexpressed with rat brain Na+ channel accessory beta1, subunit in Xenopus oocytes. Polymerase chain reaction was used for mutagenesis, and mutations were confirmed by sequencing. Na+ currents were measured using a two-microelectrode voltage clamp. Meperidine and the commonly used local anesthetic lidocaine were applied to oocytes in saline solution at room temperature. Results Meperidine and lidocaine produced tonic current inhibition with comparable concentration dependence. Meperidine caused phasic current inhibition in which the concentration-response relationship was shifted to fivefold greater concentration relative to lidocaine. Meperidine and lidocaine negatively shifted the voltage dependence of steady-state inactivation. Mutation of a putative local anesthetic receptor reduced phasic inhibition by meperidine and lidocaine and tonic inhibition by lidocaine, but not meperidine tonic inhibition. Conclusions Meperidine blocks Na+ channels with molecular pharmacologic features of a local anesthetic. The findings support classification of meperidine as a local anesthetic but with less overall potency than lidocaine.

scholarly journals Mechanisms of atrial-selective block of Na+ channels by ranolazine: II. Insights from a mathematical model

2011 ◽  
Vol 301 (4) ◽  
pp. H1615-H1624 ◽  
Author(s):  
Vladislav V. Nesterenko ◽  
Andrew C. Zygmunt ◽  
Sridharan Rajamani ◽  
Luiz Belardinelli ◽  
Charles Antzelevitch
Keyword(s):  
Action Potential ◽  
Voltage Dependence ◽  
Channel Gating ◽  
Inactivation Curve ◽  
Ventricular Cells ◽  
Kinetic Rate Constants ◽  
Steady State Inactivation ◽  
Order Of Magnitude ◽  
Action Potential Prolongation ◽  
Channel Kinetic

Block of Na+ channel conductance by ranolazine displays marked atrial selectivity that is an order of magnitude higher that of other class I antiarrhythmic drugs. Here, we present a Markovian model of the Na+ channel gating, which includes activation-inactivation coupling, aimed at elucidating the mechanisms underlying this potent atrial selectivity of ranolazine. The model incorporates experimentally observed differences between atrial and ventricular Na+ channel gating, including a more negative position of the steady-state inactivation curve in atrial versus ventricular cells. The model assumes that ranolazine requires a hydrophilic access pathway to the channel binding site, which is modulated by both activation and inactivation gates of the channel. Kinetic rate constants were obtained using guarded receptor analysis of the use-dependent block of the fast Na+ current ( INa). The model successfully reproduces all experimentally observed phenomena, including the shift of channel availability, the sensitivity of block to holding or diastolic potential, and the preferential block of slow versus fast INa. Using atrial and ventricular action potential-shaped voltage pulses, the model confirms significantly greater use-dependent block of peak INa in atrial versus ventricular cells. The model highlights the importance of action potential prolongation and of a steeper voltage dependence of the time constant of unbinding of ranolazine from the atrial Na+ channel in the development of use-dependent INa block. Our model predictions indicate that differences in channel gating properties as well as action potential morphology between atrial and ventricular cells contribute equally to the atrial selectivity of ranolazine. The model indicates that the steep voltage dependence of ranolazine interaction with the Na+ channel at negative potentials underlies the mechanism of the predominant block of INa in atrial cells by ranolazine.

scholarly journals Properties of transient K+ currents and underlying single K+ channels in rat olfactory receptor neurons.

1991 ◽  
Vol 97 (5) ◽  
pp. 1043-1072 ◽  
Author(s):  
J W Lynch ◽  
P H Barry
Keyword(s):  
Steady State ◽  
Olfactory Receptor ◽  
Olfactory Receptor Neurons ◽  
Simple Method ◽  
Small Component ◽  
Inactivation Curve ◽  
K Channels ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Receptor Neurons

The transient potassium current, IK(t), of enzymatically dissociated rat olfactory receptor neurons was studied using patch-clamp techniques. Upon depolarization from negative holding potentials, IK(t) activated rapidly and then inactivated with a time course described by the sum of two exponential components with time constants of 22.4 and 143 ms. Single-channel analysis revealed a further small component with a time constant of several seconds. Steady-state inactivation was complete at -20 mV and completely removed at -80 mV (midpoint -45 mV). Activation was significant at -40 mV and appeared to reach a maximum conductance at +40 mV (midpoint -13 mV). Deactivation was described by the sum of two voltage-dependent exponential components. Recovery from inactivation was extraordinarily slow (50 s at -100 mV) and the underlying processes appeared complex. IK(t) was reduced by 4-aminopyridine and tetraethylammonium applied externally. Increasing the external K+ concentration ([K+]o) from 5 to 25 mM partially removed IK(t) inactivation, usually without affecting activation kinetics. The elevated [K+]o also hyperpolarized the steady-state inactivation curve by 9 mV and significantly depolarized the voltage dependence of activation. Single transient K+ channels, with conductances of 17 and 26 pS, were observed in excised patches and often appeared to be localized into large clusters. These channels were similar to IK(t) in their kinetic, pharmacological, and voltage-dependent properties and their inactivation was also subject to modulation by [K+]o. The properties of IK(t) imply a role in action potential repolarization and suggest it may also be important in modulating spike parameters during neuronal burst firing. A simple method is also presented to correct for errors in the measurement of whole-cell resistance (Ro) that can result when patch-clamping very small cells. The analysis revealed a mean corrected Ro of 26 G omega for these cells.

Calcineurin-independent inhibition of KV1.3 by FK-506 (tacrolimus): a novel pharmacological property

2007 ◽  
Vol 292 (5) ◽  
pp. C1714-C1722 ◽  
Author(s):  
Hye Sook Ahn ◽  
Sung Eun Kim ◽  
Bok Hee Choi ◽  
Jin-Sung Choi ◽  
Myung-Jun Kim ◽  
...  
Keyword(s):  
Steady State ◽  
Chinese Hamster Ovary Cells ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Fk 506 ◽  
Inactivation Curve ◽  
Voltage Dependent ◽  
Dependent Inhibition ◽  
Steady State Inactivation

The interaction of FK-506 with KV1.3, stably expressed in Chinese hamster ovary cells, was investigated with the whole cell patch-clamp technique. FK-506 inhibited KV1.3 in a reversible, concentration-dependent manner with an IC50 of 5.6 μM. Rapamycin, another immunosuppressant, produced effects that were similar to those of FK-506 (IC50 = 6.7 μM). Other calcineurin inhibitors (cypermethrin or calcineurin autoinhibitory peptide) alone had no effect on the amplitude or kinetics of KV1.3. In addition, the inhibitory action of FK-506 continued, even after the inhibition of calcineurin activity. The inhibition produced by FK-506 was voltage dependent, increasing in the voltage range for channel activation. At potentials positive to 0 mV (where maximal conductance is reached), however, no voltage-dependent inhibition was found. FK-506 exhibited a strong use-dependent inhibition of KV1.3. FK-506 shifted the steady-state inactivation curves of KV1.3 in the hyperpolarizing direction in a concentration-dependent manner. The apparent dissociation constant for FK-506 to inhibit KV1.3 in the inactivated state was estimated from the concentration-dependent shift in the steady-state inactivation curve and was calculated to be 0.37 μM. Moreover, the rate of recovery from inactivation of KV1.3 was decreased. In inside-out patches, FK-506 not only reduced the current amplitude but also accelerated the rate of inactivation during depolarization. FK-506 also inhibited KV1.5 and KV4.3 in a concentration-dependent manner with IC50 of 4.6 and 53.9 μM, respectively. The present results indicate that FK-506 inhibits KV1.3 directly and that this effect is not mediated via the inhibition of the phosphatase activity of calcineurin.

Sign in / Sign up

Export Citation Format

Share Document