scholarly journals The hyperpolarization-activated current shifts the dynamic range of a voltage-dependent electrical synapse

2021 ◽  
Author(s):  
Wolfgang Stein ◽  
Margaret DeMaegd ◽  
Lena Yolanda Braun ◽  
Andrés G Vidal-Gadea ◽  
Allison L Harris ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Motor Neuron ◽  
Axon Terminal ◽  
Voltage Dependence ◽  
Dynamic Range ◽  
Complex Dynamics ◽  
Ionic Current ◽  
Electrical Synapse ◽  
Resting Membrane Potential ◽  
Voltage Dependent

Like their chemical counterparts, electrical synapses show complex dynamics such as rectification and voltage dependence that interact with other electrical processes in neurons. The consequences arising from these interactions for the electrical behavior of the synapse, and the dynamics they create, remain largely unexplored. Using a voltage-dependent electrical synapse between a descending modulatory projection neuron (MCN1) and a motor neuron (LG) in the crustacean stomatogastric ganglion, we find that the influence of the hyperpolarization-activated inward current (Ih) is critical to the function of the electrical synapse. When we blocked Ih with CsCl, the voltage dependence of the electrical synapse shifted by 18.7 mV to more hyperpolarized voltages, placing the dynamic range of the electrical synapse outside of the range of voltages used by the LG motor neuron (-60.2 mV to -44.9 mV). With dual electrode current- and voltage-clamp recordings, we demonstrate that this voltage shift is due to a sustained effect of Ih on the presynaptic MCN1 axon terminal membrane potential. Ih-induced depolarization of the axon terminal membrane potential increased the electrical postsynaptic potentials and currents. With Ih present, the axon terminal resting membrane potential depolarized, shifting the dynamic range of the electrical synapse towards the functional range of the motor neuron. We thus demonstrate that the function of an electrical synapse is critically influenced by a voltage-dependent ionic current (Ih).

scholarly journals The Role of Na,k-Atpase α Subunit Serine 775 and Glutamate 779 in Determining the Extracellular K+And Membrane Potential–Dependent Properties of the Na,k -Pump

2000 ◽  
Vol 116 (1) ◽  
pp. 47-60 ◽  
Author(s):  
R. Daniel Peluffo ◽  
José M. Argüello ◽  
Joshua R. Berlin
Keyword(s):  
Membrane Potential ◽  
Voltage Dependence ◽  
Protein Structures ◽  
Pump Current ◽  
Transmembrane Segment ◽  
Α Subunit ◽  
Voltage Dependent ◽  
Kinetics Of ◽  
Α1 Subunit

The roles of Ser775 and Glu779, two amino acids in the putative fifth transmembrane segment of the Na,K -ATPase α subunit, in determining the voltage and extracellular K + (K +o) dependence of enzyme-mediated ion transport, were examined in this study. HeLa cells expressing the α1 subunit of sheep Na,K -ATPase were voltage clamped via patch electrodes containing solutions with 115 mM Na+ (37°C). Na,K -pump current produced by the ouabain-resistant control enzyme (RD), containing amino acid substitutions Gln111Arg and Asn122Asp, displayed a membrane potential and K +o dependence similar to wild-type Na,K -ATPase during superfusion with 0 and 148 mM Na+-containing salt solutions. Additional substitution of alanine at Ser775 or Glu779 produced 155- and 15-fold increases, respectively, in the K +o concentration that half-maximally activated Na,K -pump current at 0 mV in extracellular Na+-free solutions. However, the voltage dependence of Na,K -pump current was unchanged in RD and alanine-substituted enzymes. Thus, large changes in apparent K +o affinity could be produced by mutations in the fifth transmembrane segment of the Na,K -ATPase with little effect on voltage-dependent properties of K + transport. One interpretation of these results is that protein structures responsible for the kinetics of K +o binding and/or occlusion may be distinct, at least in part, from those that are responsible for the voltage dependence of K +o binding to the Na,K -ATPase.

scholarly journals K+ currents regulate the resting membrane potential, proliferation, and contractile responses in ventricular fibroblasts and myofibroblasts

2005 ◽  
Vol 288 (6) ◽  
pp. H2931-H2939 ◽  
Author(s):  
L. Chilton ◽  
S. Ohya ◽  
D. Freed ◽  
E. George ◽  
V. Drobic ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Reversal Potential ◽  
Mechanical Activity ◽  
Resting Membrane Potential ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Primary Determinant ◽  
Inwardly Rectifying ◽  
Low K ◽  
Ionic Basis

Despite the important roles played by ventricular fibroblasts and myofibroblasts in the formation and maintenance of the extracellular matrix, neither the ionic basis for membrane potential nor the effect of modulating membrane potential on function has been analyzed in detail. In this study, whole cell patch-clamp experiments were done using ventricular fibroblasts and myofibroblasts. Time- and voltage-dependent outward K+ currents were recorded at depolarized potentials, and an inwardly rectifying K+ (Kir) current was recorded near the resting membrane potential (RMP) and at more hyperpolarized potentials. The apparent reversal potential of Kir currents shifted to more positive potentials as the external K+ concentration ([K+]o) was raised, and this Kir current was blocked by 100–300 μM Ba2+. RT-PCR measurements showed that mRNA for Kir2.1 was expressed. Accordingly, we conclude that Kir current is a primary determinant of RMP in both fibroblasts and myofibroblasts. Changes in [K+]o influenced fibroblast membrane potential as well as proliferation and contractile functions. Recordings made with a voltage-sensitive dye, DiBAC3(4), showed that 1.5 mM [K+]o resulted in a hyperpolarization, whereas 20 mM [K+]o produced a depolarization. Low [K+]o (1.5 mM) enhanced myofibroblast number relative to control (5.4 mM [K+]o). In contrast, 20 mM [K+]o resulted in a significant reduction in myofibroblast number. In separate assays, 20 mM [K+]o significantly enhanced contraction of collagen I gels seeded with myofibroblasts compared with control mechanical activity in 5.4 mM [K+]o. In combination, these results show that ventricular fibroblasts and myofibroblasts express a variety of K+ channel α-subunits and demonstrate that Kir current can modulate RMP and alter essential physiological functions.

scholarly journals Voltage- and NADPH-dependence of electron currents generated by the phagocytic NADPH oxidase

2005 ◽  
Vol 388 (2) ◽  
pp. 485-491 ◽  
Author(s):  
Gábor L. PETHEŐ ◽  
Nicolas DEMAUREX
Keyword(s):  
Membrane Potential ◽  
Nadph Oxidase ◽  
Voltage Dependence ◽  
Intrinsic Property ◽  
Maximal Activity ◽  
Underlying Mechanism ◽  
Potential Range ◽  
Electron Current ◽  
Steady State Current ◽  
Voltage Dependent

The phagocytic NADPH oxidase generates superoxide by transferring electrons from cytosolic NADPH to extracellular O2. The activity of the oxidase at the plasma membrane can be measured as electron current (Ie), and the voltage dependence of Ie was recently reported to exhibit a strong rectification in human eosinophils, with the currents being nearly voltage independent at negative potentials. To investigate the underlying mechanism, we performed voltage-clamp experiments on inside-out patches from human eosinophils activated with PMA. Electron current was evoked by bath application of different concentrations of NADPH, whereas slow voltage ramps (0.8 mV/ms), ranging from −120 to 200 mV, were applied to obtain ‘steady-state’ current–voltage relationships (I–V). The amplitude of Ie recorded at −40 mV was minimal at 8 μM NADPH and saturated above 1 mM, with half-maximal activity (Km) observed at approx. 110 μM NADPH. Comparison of I–V values obtained at different NADPH concentrations revealed that the voltage-dependence of Ie is strongly influenced by the substrate concentration. Above 0.1 mM NADPH, Ie was markedly voltage-dependent and steeply decreased with depolarization within the physiological membrane potential range (−60 to 60 mV), the I–V curve strongly rectifying only below −100 mV. At lower NADPH concentrations the I–V curve was progressively shifted to more positive potentials and Ie became voltage-independent also within the physiological range. Consequently, the Km of the oxidase decreased by approx. 40% (from 100 to 60 μM) when the membrane potential increased from −60 to 60 mV. We concluded that the oxidase activity depends on both membrane potential and [NADPH], and that the shape of the Ie–V curve is influenced by the concentration of NADPH in the submillimolar range. The surprising voltage-independence of Ie reported in whole-cell perforated patch recordings was most likely due to substrate limitation and is not an intrinsic property of the oxidase.

Ratiometry of transmembrane voltage-sensitive fluorescent dye emission in hearts

2000 ◽  
Vol 279 (3) ◽  
pp. H1421-H1433 ◽  
Author(s):  
Stephen B. Knisley ◽  
Robert K. Justice ◽  
Wei Kong ◽  
Philip L. Johnson
Keyword(s):  
Membrane Potential ◽  
Action Potentials ◽  
Signal To Noise Ratio ◽  
Green Emission ◽  
Motion Artifacts ◽  
Resting Membrane Potential ◽  
Baseline Drift ◽  
Fluorescence Measurements ◽  
Transmembrane Voltage ◽  
Voltage Dependent

Transmembrane voltage-sensitive fluorescence measurements are limited by baseline drift that can obscure changes in resting membrane potential and by motion artifacts that can obscure repolarization. Voltage-dependent shift of emission wavelengths may allow reduction of drift and motion artifacts by emission ratiometry. We have tested this for action potentials and potassium-induced changes in resting membrane potential in rabbit hearts stained with di-4-ANEPPS [Pyridinium, 4-(2-(6-(dibutylamino)-2-naphthalenyl) ethenyl)-1-(3-sulfopropyl)-, hydroxide, inner salt] using laser excitation (488 nm) and a two-photomultiplier tube system or spectrofluorometer (resolution of 500–1,000 Hz and <1 mm). Green and red emissions produced upright and inverted action potentials, respectively. Ratios of green emission to red emission followed action potential contours and exhibited larger fractional changes than either emission alone ( P < 0.001). The largest changes and signal-to-noise ratio (signal/noise) were obtained with numerator wavelengths of 525–550 nm and denominator wavelengths of 650–700 nm. Ratiometry lessened drift 56–66% ( P < 0.015) and indicated decreases in resting membrane potential. Ratiometry lessened motion artifacts and increased magnitudes of deflections representing phase-zero depolarizations relative to total deflections by 123–188% in intact hearts ( P < 0.02). Durations of action potentials at different pacing rates, temperatures, and potassium concentrations were independent of whether they were measured ratiometrically or with microelectrodes ( P ≥ 0.65). The ratiometric calibration slope was 0.017/100 mV and decreased with time. Thus emission ratiometry lessens the effects of motion and drift and indicates resting membrane potential changes and repolarization.

Physiological role of Ca(2+)-activated and voltage-dependent K+ currents in rabbit coronary myocytes

1994 ◽  
Vol 266 (6) ◽  
pp. C1523-C1537 ◽  
Author(s):  
N. Leblanc ◽  
X. Wan ◽  
P. M. Leung
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Physiological Role ◽  
Cell Voltage ◽  
Resting Membrane Potential ◽  
Physiological Level ◽  
Steady State Current ◽  
Voltage Dependent ◽  
A Minor ◽  
And Function

The properties and function of Ca(2+)-activated K+ (KCa) and voltage-dependent K+ (IK) currents of rabbit coronary myocytes were studied under whole cell voltage-clamp conditions (22 degrees C). Inhibition of KCa by tetraethylammonium chloride (1-10 mM) or charybdotoxin (50-100 nM) suppressed noisy outward rectifying current elicited by 5-s voltage steps or ramp at potentials > 0 mV, reduced the hump of the biphasic ramp current-voltage relation, and shifted by less than +5 mV the potential at which no net steady-state current is recorded (Enet; index of resting membrane potential). Inhibition of steady-state inward Ca2+ currents [ICa(L)] by nifedipine (1 microM) displaced Enet by -11 mV. Analysis of steady-state voltage dependence of IK supported the existence of a "window" current between -50 and 0 mV. 4-Aminopyridine (2 mM) blocked a noninactivating component of IK evoked between -30 and -40 mV, abolished the hump current during ramps, and shifted Enet by more than +15 mV; hump current persisted during 2-min ramp depolarizations and peaked near the maximum overlap of the steady-state activation and inactivation curves of IK (about -22 mV). A threefold rise in extracellular Ca2+ concentration (1.8-5.4 mM) enhanced time-dependent outward K+ current (6.7-fold at +40 mV) and shifted Enet by -30 mV. It is concluded that, under steady-state conditions, IK and ICa(L) play a major role in regulating resting membrane potential at a physiological level of intracellular Ca2+ concentration, with a minor contribution from KCa. However, elevation of intracellular Ca2+ concentration enhances KCa and hyperpolarizes the myocyte to limit Ca2+ entry through ICa(L).

Calcium channels, potassium channels, and voltage dependence of arterial smooth muscle tone

1990 ◽  
Vol 259 (1) ◽  
pp. C3-C18 ◽  
Author(s):  
M. T. Nelson ◽  
J. B. Patlak ◽  
J. F. Worley ◽  
N. B. Standen
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Katp Channel ◽  
Voltage Dependence ◽  
Muscle Tone ◽  
Ca Channels ◽  
Resistance Arteries ◽  
Arterial Smooth Muscle ◽  
Membrane Hyperpolarization ◽  
Voltage Dependent

Resistance arteries exist in a maintained contracted state from which they can dilate or constrict depending on need. In many cases, these arteries constrict to membrane depolarization and dilate to membrane hyperpolarization and Ca-channel blockers. We discuss recent information on the regulation of arterial smooth muscle voltage-dependent Ca channels by membrane potential and vasoconstrictors and on the regulation of membrane potential and K channels by vasodilators. We show that voltage-dependent Ca channels in the steady state can be open and very sensitive to membrane potential changes in a range that occurs in resistance arteries with tone. Many synthetic and endogenous vasodilators act, at least in part, through membrane hyperpolarization caused by opening K channels. We discuss evidence that these vasodilators act on a common target, the ATP-sensitive K (KATP) channel that is inhibited by sulfonylurea drugs. We propose the following hypotheses that presently explain these findings: 1) arterial smooth muscle tone is regulated by membrane potential primarily through the voltage dependence of Ca channels; 2) many vasoconstrictors act, in part, by opening voltage-dependent Ca channels through membrane depolarization and activation by second messengers; and 3) many vasodilators work, in part, through membrane hyperpolarization caused by KATP channel activation.

Sodium dependence of the thyrotrophin-induced depolarization in cultured porcine thyroid cells

1986 ◽  
Vol 108 (2) ◽  
pp. 225-230 ◽  
Author(s):  
T. A. Hambleton ◽  
J. R. Bourke ◽  
G. J. Huxham ◽  
S. W. Manley
Keyword(s):  
Membrane Potential ◽  
Action Potentials ◽  
Potassium Concentration ◽  
Sodium Current ◽  
Resting Membrane Potential ◽  
Thyroid Cell ◽  
Free Medium ◽  
Thyroid Cells ◽  
Voltage Dependent ◽  
Sodium And Potassium

ABSTRACT Cultured porcine thyroid cells exhibit a resting membrane potential of about − 73 mV and depolarize to about − 54 mV on exposure to TSH. The depolarizing response to TSH was preserved in a medium consisting only of inorganic salts and buffers, but was abolished in sodium-free medium, demonstrating dependence on an inward sodium current. Increasing the potassium concentration of the medium resulted in a reduction in the resting membrane potential of 60 mV per tenfold change in potassium concentration, and a diminished TSH response. A hyperpolarizing TSH response was observed in a sodium- and bicarbonate-free medium, indicating that a hyperpolarizing ion current (probably carried by potassium) was also enhanced in the presence of TSH. Tetrodotoxin blocked the TSH response. We conclude that the response of the thyroid cell membrane to TSH involves increases in permeability to sodium and potassium, and that the thyroid membrane ion channels bear some similarity to the voltage-dependent sodium channels of excitable tissues, despite the absence of action potentials in the thyroid. J. Endocr. (1986) 108, 225–230

Charybdotoxin block of Ca2+-activated K+ channels in colonic muscle depends on membrane potential dynamics

1998 ◽  
Vol 274 (3) ◽  
pp. C673-C680 ◽  
Author(s):  
Bret W. Frey ◽  
Andreas Carl ◽  
Nelson G. Publicover
Keyword(s):  
Membrane Potential ◽  
Longitudinal Muscle ◽  
Circular Muscle ◽  
Resting Membrane Potential ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Rate Of Increase ◽  
Voltage Dependent ◽  
Simple Kinetic Model

Charybdotoxin (ChTX) is a specific blocker of Ca2+-activated K+ channels. The voltage- and time-dependent dynamics of ChTX block were investigated using canine colonic myocytes and the whole cell patch-clamp technique with step and ramp depolarization protocols. During prolonged step depolarizations, K+ current slowly increased in the continued presence of ChTX (100 nM). The rate of increase depended on membrane potential with an e-fold change for every 60 mV. During ramp depolarizations, the effectiveness of ChTX block depended significantly on the rate of the ramp (50% at 0.01 V/s to 80% at 0.5 V/s). Results are consistent with a mechanism in which ChTX slowly “unbinds” in a voltage-dependent manner. A simple kinetic model was developed in which ChTX binds to both open and closed states. Slow unbinding is consistent with ChTX having little effect on electrical slow waves recorded from circular muscle while causing depolarization and contraction of longitudinal muscle, which displays more rapid “spikes.” Resting membrane potential and membrane potential dynamics are important determinants of ChTX action.

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)

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