Developmental Regulation of Whole Cell Capacitance and Membrane Current in Identified Interneurons in C. elegans

2006 ◽  
Vol 95 (6) ◽  
pp. 3665-3673 ◽  
Author(s):  
Serge Faumont ◽  
Thomas Boulin ◽  
Oliver Hobert ◽  
Shawn R. Lockery
Keyword(s):  
Time Course ◽  
Homeobox Gene ◽  
Outward Current ◽  
Cell Voltage ◽  
Membrane Current ◽  
Immunoglobulin Superfamily ◽  
Loss Of Function ◽  
Whole Cell ◽  
Steady State Current ◽  
Cell Capacitance

Postembryonic developmental changes in electrophysiological properties of the AIY interneuron class were investigated using whole cell voltage clamp. AIY interneurons displayed an increase in cell capacitance during larval development, whereas steady-state current amplitude did not increase. The time course of the outward membrane current, carried at least in part by K+ ions, matured, from a slowly activating, sustained current to a rapidly activating, decaying current. We also investigated how the development of capacitance and outward current was altered by loss-of-function mutations in genes expressed in AIY. One such gene, the LIM homeobox gene ttx-3, is known to be involved in the specification of the AIY neuronal subtype. In ttx-3 mutants, capacitance and outward current matured precociously. In mutants of the gene wrk-1, an immunoglobulin superfamily (IgSF) member whose expression is regulated by ttx-3, capacitance matured normally, whereas outward current matured precociously. We conclude that AIY interneurons contain distinct pathways for regulating capacitance and membrane current.

scholarly journals Lipopolysaccharide prolongs action potential duration in HL-1 mouse cardiomyocytes

2012 ◽  
Vol 303 (8) ◽  
pp. C825-C833 ◽  
Author(s):  
Robert Wondergem ◽  
Bridget M. Graves ◽  
Chuanfu Li ◽  
David L. Williams
Keyword(s):  
Action Potential ◽  
Action Potential Duration ◽  
Salmonella Enteritidis ◽  
Time Course ◽  
Outward Current ◽  
Cell Voltage ◽  
Delayed Rectifier ◽  
Maximal Effect ◽  
Cellular Mechanisms ◽  
Whole Cell

Sepsis has deleterious effects on cardiac function including reduced contractility. We have shown previously that lipopolysaccharides (LPS) directly affect HL-1 cardiac myocytes by inhibiting Ca2+ regulation and by impairing pacemaker “funny” current, If. We now explore further cellular mechanisms whereby LPS inhibits excitability in HL-1 cells. LPS (1 μg/ml) derived from Salmonella enteritidis decreased rate of firing of spontaneous action potentials in HL-1 cells, and it increased their pacemaker potential durations and decreased their rates of depolarization, all measured by whole cell current clamp. LPS also increased action potential durations and decreased their amplitude in cells paced at 1 Hz with 0.1 nA, and 20 min were necessary for maximal effect. LPS decreased the amplitude of a rapidly inactivating inward current attributed to Na+ and of an outward current attributed to K+; both were measured by whole cell voltage clamp. The K+ currents displayed a resurgent outward tail current, which is characteristic of the rapid delayed-rectifier K+ current, IKr. LPS accordingly reduced outward currents measured with pipette Cs+ substituted for K+ to isolate IKr. E-4031 (1 μM) markedly inhibited IKr in HL-1 cells and also increased action potential duration; however, the direct effects of E-4031 occurred minutes faster than the slow effects of LPS. We conclude that LPS increases action potential duration in HL-1 mouse cardiomyocytes by inhibition of IKr and decreases their rate of firing by inhibition of INa. This protracted time course points toward an intermediary metabolic event, which either decreases available mouse ether-a-go-go (mERG) and Na+ channels or potentiates their inactivation.

scholarly journals Properties of "creep currents" in single frog atrial cells.

1986 ◽  
Vol 87 (6) ◽  
pp. 833-855 ◽  
Author(s):  
J R Hume ◽  
A Uehara
Keyword(s):  
Time Course ◽  
Outward Current ◽  
Membrane Current ◽  
K Channel ◽  
Transient Outward Current ◽  
Ca Channel ◽  
Purkinje Fibers ◽  
Atrial Cells ◽  
Cardiac Purkinje Fibers ◽  
Inward Currents

Changes in membrane current in response to an elevation of [Na]i were studied in enzymatically dispersed frog atrial cells. Na loading by either intracellular dialysis or exposure to the Na ionophore monensin produces changes in membrane current that resemble the "creep currents" originally observed in cardiac Purkinje fibers during exposure to low-K solutions. Na loading induces a transient outward current during depolarizing voltage-clamp pulses, followed by an inward current in response to repolarization back to the holding potential. In contrast to cardiac Purkinje fibers, Na loading of frog atrial cells induces creep currents without accompanying transient inward currents. Creep currents induced by Na loading are insensitive to K channel antagonists like Cs and 4-aminopyridine; they are not influenced by doses of Ca channel antagonists that abolish iCa, but are sensitive to changes in [Ca]o or [Na]o. A comparison of the time course of development of inward creep currents are not tail currents associated with iCa. Inward creep currents can also be induced by experimental interventions that increase the iCa amplitude. Exposure to isoproterenol enhances the iCa amplitude and induces inward creep currents; both can be attenuated by Ca channel antagonists. Both inward and outward creep currents are blocked by low doses of La, independently of La's ability to block iCa. It is concluded that (a) creep currents are not mediated by voltage-gated Na, Ca, or K channels or by an electrogenic Na,K pump; (b) inward creep currents induced either by Na loading or in response to an increase in the amplitude of iCa are triggered by an elevation of [Ca]i; and (c) creep currents may be generated by either an electrogenic Na/Ca exchange mechanism or by a nonselective cation channel activated by [Ca]i.

scholarly journals A selective 5-HT1a receptor agonist improves respiration in a mouse model of Rett syndrome

2013 ◽  
Vol 115 (11) ◽  
pp. 1626-1633 ◽  
Author(s):  
Erica S. Levitt ◽  
Barbara J. Hunnicutt ◽  
Sharon J. Knopp ◽  
John T. Williams ◽  
John M. Bissonnette
Keyword(s):  
Rett Syndrome ◽  
Binding Protein ◽  
Glutamate Release ◽  
Outward Current ◽  
Cell Voltage ◽  
Equilibrium Potential ◽  
Maximal Effect ◽  
Dependent Manner ◽  
Male Mice ◽  
Loss Of Function

Rett syndrome is a neurological disorder caused by loss of function mutations in the gene that encodes the DNA binding protein methyl-CpG-binding protein 2 (Mecp2). A prominent feature of the syndrome is disturbances in respiration characterized by frequent apnea and an irregular interbreath cycle. 8-Hydroxy-2-dipropylaminotetralin has been shown to positively modulate these disturbances (Abdala AP, Dutschmann M, Bissonnette JM, Paton JF, Proc Natl Acad Sci U S A 107: 18208–18213, 2010), but the mode of action is not understood. Here we show that the selective 5-HT1a biased agonist 3-chloro-4-fluorophenyl-(4-fluoro-4-{[(5-methylpyrimidin-2-ylmethyl)-amino]-methyl}-piperidin-1-yl)-methanone (F15599) decreases apnea and corrects irregularity in both heterozygous Mecp2-deficient female and in Mecp2 null male mice. In whole cell voltage-clamp recordings from dorsal raphe neurons, F15599 potently induced an outward current, which was blocked by barium, reversed at the potassium equilibrium potential, and was antagonized by the 5-HT1a antagonist WAY100135. This is consistent with somatodendritic 5-HT1a receptor-mediated activation of G protein-coupled inwardly rectifying potassium channels (GIRK). In contrast, F15599 did not activate 5-HT1b/d receptors that mediate inhibition of glutamate release from terminals in the nucleus accumbens by a presynaptic mechanism. Thus F15599 activated somatodendritic 5-HT1a autoreceptors, but not axonal 5-HT1b/d receptors. In unanesthetized Mecp2-deficient heterozygous female mice, F15599 reduced apnea in a dose-dependent manner with maximal effect of 74.5 ± 6.9% at 0.1 mg/kg and improved breath irrregularity. Similarly, in Mecp2 null male mice, apnea was reduced by 62 ± 6.6% at 0.25 mg/kg, and breathing became regular. The results indicate respiration is improved with a 5-HT1a agonist that activates GIRK channels without affecting neurotransmitter release.

Differences in rate dependence of transient outward current in rabbit and human atrium

1992 ◽  
Vol 263 (6) ◽  
pp. H1747-H1754 ◽  
Author(s):  
B. Fermini ◽  
Z. Wang ◽  
D. Duan ◽  
S. Nattel
Keyword(s):  
Time Course ◽  
Outward Current ◽  
Cell Voltage ◽  
Rate Dependence ◽  
Transient Outward Current ◽  
Human Atrium ◽  
Rate Dependency ◽  
Heart Rates ◽  
Pharmacological Regulation ◽  
Atrial Repolarization

Both human and rabbit atrial cells possess a large 4-aminopyridine-sensitive transient outward current (I(to1)). However, the slow reactivation of this current in rabbits suggests that its role may be limited to very slow heart rates. We used whole cell voltage-clamp recordings to evaluate the rate dependency of I(to1) in rabbit and human atrial myocytes. Our results show that at physiological temperatures in human atrium, I(to1) is rate independent at rates between 0.1 and 4.0 Hz. Peak I(to1) at 4.0 Hz in rabbit was 3.4 +/- 1.4% (mean +/- SE) of current at 0.1 Hz (P < 0.001, n = 8), whereas in humans, peak I(to1) at 4.0 Hz averaged 88.8 +/- 6.1% of the current at 0.1 Hz (P > 0.05, n = 7). These differences were due to marked discrepancies in reactivation time course, which was biexponential with time constants that averaged 650 +/- 159 ms and 8.4 +/- 1.1 s in rabbit (n = 8) compared with a single exponential time constant of 33.6 +/- 6.8 ms (n = 8) in human atrium (both at 30 degrees C). These findings suggest that I(to1) can contribute importantly to atrial repolarization at all physiological heart rates in humans. Furthermore, these results emphasize that there are important interspecies variations in the rate dependence of I(to1), which need to be considered in understanding the physiological and pharmacological regulation of atrial repolarization.

Four different components contribute to outward current in rat ventricular myocytes

1999 ◽  
Vol 277 (1) ◽  
pp. H107-H118 ◽  
Author(s):  
Herbert M. Himmel ◽  
Erich Wettwer ◽  
Qi Li ◽  
Ursula Ravens
Keyword(s):  
Steady State ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Cell Voltage ◽  
Differential Sensitivity ◽  
Resting Potential ◽  
Residual Fraction ◽  
Voltage Range ◽  
Rat Ventricular Myocytes ◽  
Steady State Current

In rat ventricle, two Ca2+-insensitive components of K+ current have been distinguished kinetically and pharmacologically, the transient, 4-aminopyridine (4-AP)-sensitive I to and the sustained, tetraethylammonium (TEA)-sensitive I K. However, a much greater diversity of depolarization-activated K+ channels has been reported on the level of mRNA and protein. In the search for electrophysiological evidence of further current components, the whole cell voltage-clamp technique was used to analyze steady-state inactivation of outward currents by conditioning potentials in a wide voltage range. Peak ( I peak) and late ( I late) currents during the test pulse were analyzed by Boltzmann curve fitting, producing three fractions each. Fractions a and b had different potentials of half-maximum inactivation ( V 0.5); the third residual fraction, r, did not inactivate. Fractions a for I peak and I late had similar relative amplitudes and V 0.5 values, whereas size and V 0.5 of fractions b differed significantly between I peak and I late. Only b of I peak was transient, suggesting a relation with I to, whereas a, b, and r of I late appeared to be three different sustained currents. Therefore, four individual outward current components were distinguished: I to( b of I peak), I K( a), the steady-state current I ss( r), and the novel current I Kx( b of I late). This was further supported by differential sensitivity to TEA, 4-AP, clofilium, quinidine, dendrotoxin, heteropodatoxin, and hanatoxin. With the exception of I to, none of the currents exhibited a marked transmural gradient. Availability of I K was low at resting potential; nevertheless, I K contributed to action potential shortening in hyperpolarized subendocardial myocytes. In conclusion, on the basis of electrophysiological and pharmacological evidence, at least four components contribute to outward current in rat ventricular myocytes.

Whole-cell voltage-clamp study of the fading of GABA-activated currents in acutely dissociated hippocampal neurons

1986 ◽  
Vol 56 (1) ◽  
pp. 1-18 ◽  
Author(s):  
J. R. Huguenard ◽  
B. E. Alger
Keyword(s):  
Steady State ◽  
Voltage Clamp ◽  
Time Course ◽  
Reversal Potential ◽  
Cell Voltage ◽  
Membrane Properties ◽  
Equilibrium Potential ◽  
Spinal Cord Neurons ◽  
Whole Cell ◽  
Whole Cell Voltage Clamp

The lability of the responses of mammalian central neurons to gamma-aminobutyric acid (GABA) was studied using neurons acutely dissociated from the CA1 region of the adult guinea pig hippocampus as a model system. GABA was applied to the neuronal somata by pressure ejection and the resulting current (IGABA) recorded under whole-cell voltage clamp. In initial experiments we examined several basic properties of cells in this preparation. Our data confirm that passive and active membrane properties are similar to those which characterize cells in other preparations. In addition, GABA-dependent conductance (gGABA), reversal potential (EGABA), and the interaction of GABA with pentobarbital and bicuculline all appeared to be normal. Dendritic GABA application could cause depolarizing GABA responses, and somatic GABA application caused hyperpolarizations due to chloride (Cl-) movements. Repetitive brief applications (5-15 ms) of GABA (10(-5) to 10(-3) M) at a frequency of 0.5 Hz led to fading of successive peaks of IGABA until, at a given holding potential, a steady state was reached in which IGABA no longer changed. Imposing voltage steps lasting seconds during a train of steady-state GABA responses led initially to increased IGABA that then diminished with maintenance of the step voltage. The rate of decrease of IGABA at each new holding potential was independent of the polarity of the step in holding potential but was highly dependent on the rate of GABA application. Application rates as low as 0.05 Hz led to fading of IGABA, even with activation of relatively small conductances (5-15 nS). Since IGABA evoked by somatic GABA application in these cells is carried by Cl-, the Cl- equilibrium potential (ECl) is equal to the reversal potential for IGABA, i.e., to EGABA. The fading of IGABA with changes in holding potential can be almost entirely accounted for by a shift in ECl resulting from transmembrane flux of Cl- through the GABA-activated conductance. Maneuvers that prevent changes in the intracellular concentration of Cl-ions, [Cl-]i, including holding the membrane potential at EGABA during repetitive GABA application or buffering [Cl-]i with high pipette [Cl-], prevent changes in EGABA. Desensitization of the GABA response (an actual decrease in gGABA) occurs in these neurons during prolonged application of GABA (greater than 1 s) but with a slower time course than changes in EGABA. Whole-cell voltage-clamp techniques applied to tissue-cultured spinal cord neurons indicated that rapid shifts in EGABA result from repetitive GABA application in these cells as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Whole-cell recording of light-evoked photoreceptor responses in a slice preparation of the cuttlefish retina

2005 ◽  
Vol 22 (3) ◽  
pp. 359-370 ◽  
Author(s):  
ABDESSLAM CHRACHRI ◽  
LISA NELSON ◽  
RODDY WILLIAMSON
Keyword(s):  
Time Course ◽  
Early Stage ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
Slice Preparation ◽  
Whole Cell ◽  
Inward Current ◽  
Transient Inward Current ◽  
Dose Dependent

A new tissue slice preparation of the cuttlefish eye is described that permits patch-clamp recordings to be acquired from intact photoreceptors during stimulation of the retina with controlled light flashes. Whole-cell recordings using this preparation, from the retinas of very youngSepia officinalisdemonstrated that the magnitude, latency, and kinetics of the flash-induced photocurrent are closely dependent on the magnitude of the flash intensity. Depolarizing steps to voltages more positive than −40 mV, from a membrane holding potential of −60 mV, induced a transient inward current followed by a larger, more sustained outward current in these early-stage photoreceptors. The latter current resembled the delayed rectifier (IK) already identified in many other nerve cells, including photoreceptors. This current was activated at −30 mV from a holding potential of −60 mV, had a sustained time course, and was blocked in a dose-dependent manner by tetraethylammonium chloride (TEA). The smaller, transient, inward current appeared at potentials more positive than −50 mV, reached peak amplitude at −30 mV and decreased with further depolarization. This current was characterized as the sodium current (INa) on the basis that it was inactivated at holding potentials above −40 mV, was blocked by tetrodotoxin (TTX) and was insensitive to cobalt.Intracellular perfusion of the photoreceptors,viathe patch pipette, demonstrated that U-73122 and heparin blocked the evoked photocurrent in a dose-dependent manner, suggesting the involvement of the phospholipase C (PLC) and inositol 1,4,5-triphosphate (InsP3), respectively, in the phototransduction cascade. Perfusion with cyclic GMP increased significantly the evoked photocurrent, while the inclusion of phorbol-12,13-dibutyrate reduced significantly the evoked photocurrent, supporting the involvement of cGMP and the diacylglycerol (DAG) pathways, respectively, in the cuttlefish transduction process.

scholarly journals A pH-sensitive and voltage-dependent proton conductance in the plasma membrane of macrophages.

1993 ◽  
Vol 102 (4) ◽  
pp. 729-760 ◽  
Author(s):  
A Kapus ◽  
R Romanek ◽  
A Y Qu ◽  
O D Rotstein ◽  
S Grinstein
Keyword(s):  
Time Course ◽  
Reversal Potential ◽  
Outward Current ◽  
Peritoneal Macrophages ◽  
Equilibrium Potential ◽  
Acid Uptake ◽  
Similar Time ◽  
Cytosolic Ph ◽  
Whole Cell ◽  
Voltage Dependent

Phagocytes generate large amounts of metabolic acid during activation. Therefore, the presence of a conductive pathway capable of H+ extrusion has been suggested (Henderson, L. M., J. B. Chappell, and O. T. G. Jones. 1987. Biochemical Journal. 246:325-329). In this report, electrophysiological and fluorimetric methods were used to probe the existence of a H+ conductance in murine peritoneal macrophages. In suspended cells, recovery of the cytosolic pH (pHi) from an acid-load in Na+ and HCO3(-)-free medium was detectable in depolarizing but not in hyperpolarizing media. The rate of alkalinization was potentiated by the rheogenic ionophore valinomycin. These findings are consistent with the existence of a conductive H+ (equivalent) pathway. This notion was confirmed by patch-clamping and fluorescence ratio measurements of single adherent cells. When voltage was clamped in the whole-cell configuration, depolarizing pulses induced a sizable outward current which was accompanied by cytosolic alkalinization. Several lines of evidence indicate that H+ (equivalents) carry this current: (a) the conductance was unaffected by substitution of the major ionic constituents of the intra-and/or extracellular media, (b) the reversal potential of the tail currents approached the H+ equilibrium potential; and (c) the voltage-induced currents and pHi changes were both Zn2+ sensitive and had similar time course and potential dependence. The peak whole-cell current displayed marked outward rectification and was exquisitely H+ selective. At constant voltage, the H+ permeability was increased by lowering pHi but was inhibited by extracellular acidification. Together with the voltage dependence of the conductance, these features ensure that H+ extrusion can occur during activation, while potentially deleterious acid uptake is precluded. The properties of the conductance appear ideally suited for pHi regulation during phagocyte activation, because these cells undergo a sustained depolarization and an incipient acidification when stimulated. Comparison of the magnitude of the current with the amount of metabolic acid generated during macrophage activation indicates that the conductance is sufficiently large to contribute to the H+ extrusion required for maintenance of pHi.

Antagonistic Modulation of a Hyperpolarization-Activated Cl– Current in Aplysia Sensory Neurons by SCPB and FMRFamide

2003 ◽  
Vol 90 (2) ◽  
pp. 586-598 ◽  
Author(s):  
Ned Buttner ◽  
Steven A. Siegelbaum
Keyword(s):  
Sensory Neurons ◽  
Reversal Potential ◽  
Outward Current ◽  
Cell Voltage ◽  
High Concentration ◽  
Pipette Solution ◽  
Whole Cell ◽  
Whole Cell Recording ◽  
Type K ◽  
Cell Recording

Whole cell voltage-clamp recordings from Aplysia mechanosensory neurons obtained from the pleural ganglion were used to investigate the actions on membrane currents of the neuropeptides SCPB and FMRFamide. At the start of whole cell recording, SCPB typically evoked an inward current at a holding potential of –40 mV, due to the cAMP-mediated closure of the S-type K+ channel, whereas FMRFamide evoked an outward current, due to the opening of the S-type K+ channels mediated by 12-lipoxygenase metabolites of arachidonic acid. However, after several minutes of whole cell recording with a high concentration of chloride in the whole cell patch pipette solution, the responses to SCPB and FMRF-amide at –40 mV were inverted; SCPB evoked an outward current, whereas FMRFamide and YGGFMRFamide evoked inward currents. Ion substitution experiments and reversal potential measurements revealed that these responses were due to the opposing regulation of a Cl– current, whose magnitude was greatly enhanced by dialysis with the high Cl–-containing pipette solution. SCPB inhibited this Cl– current through production of cAMP and activation of PKA. YGGFMRFamide activated this Cl– current by stimulating a cGMP-activated phosphodiesterase that hydrolyzed cAMP. Thus a cAMP-dependent Cl– current undergoes antagonistic modulation by two neuropeptides in Aplysia sensory neurons.

Sign in / Sign up

Export Citation Format

Share Document