Role of nonselective cation current in muscarinic responses of canine colonic muscle

1993 ◽  
Vol 265 (6) ◽  
pp. C1463-C1471 ◽  
Author(s):  
H. K. Lee ◽  
O. Bayguinov ◽  
K. M. Sanders
Keyword(s):  
Divalent Cations ◽  
Reversal Potential ◽  
Outward Current ◽  
Cell Voltage ◽  
Isolated Cells ◽  
Cation Current ◽  
Cation Conductance ◽  
Voltage Dependent ◽  
Patch Technique

The mechanism of muscarinic excitation was studied in colonic muscle strips and isolated cells. In whole cell voltage-clamp studies performed at 33 degrees C utilizing the permeabilized patch technique, acetylcholine (ACh) reduced an L-type Ca2+ current. With K+ currents blocked, depolarization to positive potentials in the presence of ACh elicited outward current. Difference currents showed that ACh activated a voltage-dependent current that reversed at about -8 mV; this current (IACh) had properties similar to the nonselective cation conductance found in other smooth muscle cells. The reversal potential of IACh shifted toward negative potentials when external Na+ was reduced, and the inward current elicited at -70 mV decreased when external Na+ was reduced. IACh was facilitated by internal Ca2+. After the current was activated at a holding potential of -70 mV, depolarizations to -30 to 0 mV elicited influx of Ca2+ via voltage-dependent Ca2+ channels. After repolarization to the holding potential, a large inward tail current was observed. IACh was blocked by Ni2+ and Cd2+ at concentrations of 100 microM or less. Quinine (0.5 mM) also blocked IACh. With the use of the sensitivity of IACh to reduced external Na+ and divalent cations, the role of IACh in responses of intact muscles to ACh was examined. When external Na+ was reduced, ACh failed to increase slow-wave duration, and Ni2+ (50 microM) reversed the depolarization caused by ACh. These data suggest an important role for IACh in the electrical responses of colonic muscles. The contribution of IACh appears to prolong slow waves, which would allow greater entry of Ca2+ and increased force development.

Zn2+ Blocks the NMDA- and Ca2+-Triggered Postexposure Current I pe in Hippocampal Pyramidal Cells

1998 ◽  
Vol 79 (2) ◽  
pp. 1124-1126 ◽  
Author(s):  
Qiang X. Chen ◽  
Katherine L. Perkins ◽  
Robert K. S. Wong
Keyword(s):  
Divalent Cations ◽  
Pyramidal Cells ◽  
Cell Voltage ◽  
Continuous Growth ◽  
Ca1 Pyramidal Cells ◽  
Cation Current ◽  
Hippocampal Ca1 ◽  
Intracellular Ca ◽  
Hippocampal Pyramidal Cells

Chen, Qiang X., Katherine L. Perkins, and Robert K. S. Wong. Zn2+ blocks the NMDA- and Ca2+-triggered postexposure current I pe in hippocampal pyramidal cells. J. Neurophysiol. 79: 1124–1126, 1998. Whole cell voltage-clamp recordings from acutely isolated hippocampal CA1 pyramidal cells from adult guinea pigs were used to evaluate divalent cations as possible blockers of the postexposure current ( I pe). I pe is a cation current that is triggered by the rise in intracellular Ca2+ concentration that occurs after the application of a toxic level of N-methyl-d-aspartate (NMDA). Once triggered, I pe continues to grow until death of the neuron occurs. I pe may be a critical link between transient NMDA exposure and cell death. I pe was blocked by micromolar concentrations of Zn2+. The Zn2+ effect had an IC50 of 64 μM and saturated at 500 μM. Prolonged Zn2+ block of I pe revealed that the maintenance of a steady I pe is not dependent on I pe-mediated Ca2+ influx but that the continuous growth in I pe is dependent on I pe-mediated Ca2+ influx. The availability of an effective blocker of I pe should facilitate the investigation of the intracellular activation pathway of I pe and the role of I pe in neuronal death.

Characterization of a transient outward K+ current with inward rectification in canine ventricular myocytes

1998 ◽  
Vol 274 (3) ◽  
pp. C577-C585 ◽  
Author(s):  
Gui-Rong Li ◽  
Haiying Sun ◽  
Stanley Nattel
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Outward Current ◽  
Equilibrium Potential ◽  
Inward Rectification ◽  
Transient Outward Current ◽  
Membrane Excitability ◽  
Voltage Dependent ◽  
Patch Technique

The threshold potential for the classical depolarization-activated transient outward K+ current and Cl− current is positive to −30 mV. With the whole cell patch technique, a transient outward current was elicited in the presence of 5 mM 4-aminopyridine (4-AP) and 5 μM ryanodine at voltages positive to the K+ equilibrium potential in canine ventricular myocytes. The current was abolished by 200 μM Ba2+ or omission of external K+([Formula: see text]) and showed biexponential inactivation. The current-voltage relation for the peak of the transient outward component showed moderate inward rectification. The transient outward current demonstrated voltage-dependent inactivation (half-inactivation voltage: −43.5 ± 3.2 mV) and rapid, monoexponential recovery from inactivation (time constant: 13.2 ± 2.5 ms). The reversal potential responded to the changes in[Formula: see text] concentration. Action potential clamp revealed two phases of Ba2+-sensitive current during the action potential, including a large early transient component after the upstroke and a later outward component during phase 3 repolarization. The present study demonstrates that depolarization may elicit a Ba2+- and[Formula: see text]-sensitive, 4-AP-insensitive, transient outward current with inward rectification in canine ventricular myocytes. The properties of this K+ current suggest that it may carry a significant early outward current upon depolarization that may play a role in determining membrane excitability and action potential morphology.

External anions and volume-sensitive anion current in guinea-pig ventricular myocytes

2000 ◽  
Vol 78 (8) ◽  
pp. 662-668 ◽  
Author(s):  
Lesya M Shuba ◽  
Terence F McDonald
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Outward Current ◽  
Cell Voltage ◽  
Dependent Manner ◽  
Free Solution ◽  
Relative Permeabilities ◽  
Voltage Dependent ◽  
Relative Slope

The objective of this study was to determine the effects of anion replacement on volume-sensitive anion current in guinea-pig ventricular myocytes. Myocytes in the conventional whole-cell voltage-clamp configuration were superfused and dialysed with Na+-, K+-, and Ca2+-free solution, and exposed to external 75 mM Cl- solution of one-half normal osmolality. Prolonged exposures to hyposmotic solution promoted the development of outwardly-rectifying currents that were inactivated at high positive potentials and reversed in a Cl--dependent manner (50 mV per decade pipette Cl- concentration). Replacement of external Cl- by iodide and aspartate affected the reversal potential (Erev) and slope conductance of the volume-sensitive current. Relative permeabilities calculated from changes in Erev were 1.49 ± 0.09, 1.00, and 0.29 ± 0.04 for iodide, Cl-, and aspartate, respectively; relative slope conductances between Erev and Erev + 40 mV were 1.21 ± 0.09, 1.00, and 0.43 ± 0.07, respectively. Replacement of Cl- also affected the time dependence of the volume-sensitive current; replacement by iodide reversibly enhanced the decay of outward current at positive potentials, whereas replacement by aspartate reduced it. These results are compared with earlier findings on non-cardiac time- and voltage-dependent anion current activated by hyposmotic solution.Key words: hyposmotic solution, Cl- current, iodide, aspartate, permeability, conductance.

Selective expression of transient outward currents in different types of acutely isolated hippocampal interneurons

1996 ◽  
Vol 76 (5) ◽  
pp. 3563-3567 ◽  
Author(s):  
S. H. Fan ◽  
R. K. Wong
Keyword(s):  
Outward Current ◽  
Pyramidal Cells ◽  
Cell Voltage ◽  
Transient Outward Current ◽  
Isolated Cells ◽  
Tissue Slices ◽  
Ca1 Region ◽  
Hippocampal Ca1 Region ◽  
Outward Currents ◽  
Voltage Dependent

1. Voltage-dependent outward currents in CA1 interneurons were studied with the use of whole cell voltage-clamp techniques. Tissue slices containing strata lacunosum-moleculare and radiatum (L-M-R regions) of the hippocampal CA1 region were prepared. Neurons were then isolated from these tissue slices with the use of an acute dissociation procedure. The morphologies of the isolated neurons were distinct from those of pyramidal cells and correlated with those of interneurons identified in the L-M-R regions after immunohistochemical stainings. 2. Total outward currents were elicited from the isolated cells by depolarization steps applied after a 300-ms hyperpolarization prepulse to 100 mV from a holding potential of 50 mV. Delayed outward currents were obtained by intercalating a 120-ms step at 55 mV between the hyperpolarizing prepulse and the depolarization. The intercalating step served to inactivate transient outward currents. Transient outward current were isolated by subtracting the delayed outward currents from the total outward currents. 3. Interneurons were subgrouped on the basis of their ability to produce transient outward current in response to the above protocol. 4. The two groups of interneurons possessed distinct morphological features. Cells producing transient outward currents had polygonal-shaped somata with thick primary processes that gave rise to smaller secondary processes at a short distance from the soma. Interneurons without activatable transient outward currents had somata that were not polygonal and they had more slender primary dendritic processes. 5. These results suggest that interneurons in the L-M-R regions can be divided into two groups on the basis of the presence or absence of voltage-dependent transient outward currents. The two groups of cells differentiated on this basis also have distinguishable morphological traits. The difference in the properties of the outward current may be a factor contributing to the variation in the firing pattern of recorded interneurons reported in previous studies.

Membrane depolarization in PC-12 cells during hypoxia is regulated by an O2-sensitive K+ current

1996 ◽  
Vol 271 (2) ◽  
pp. C658-C665 ◽  
Author(s):  
W. H. Zhu ◽  
L. Conforti ◽  
M. F. Czyzyk-Krzeska ◽  
D. E. Millhorn
Keyword(s):  
Membrane Potential ◽  
Reversal Potential ◽  
Outward Current ◽  
Cell Voltage ◽  
Membrane Depolarization ◽  
Resting Membrane Potential ◽  
Current Clamp ◽  
Pc 12 Cells ◽  
Current Voltage ◽  
K Current

The effects of hypoxia on K+ current (IK), resting membrane potential, and cytosolic free Ca2+ in rat pheochromocytoma (PC-12) cells were studied. Whole cell voltage- and current-clamp experiments were performed to measure IK and membrane potential, respectively. Cytosolic free Ca2+ level was measured using the Ca(2+)-sensitive fluorescent dye fura 2. Depolarizing voltage steps to +50 mV from a holding potential of -90 mV elicited a slowly inactivating, tetraethylammonium chloride-sensitive, and Ca(2+)-insensitive IK that was reversibly inhibited by reduced O2 tension. Graded reduction in PO2 (from 150 to 0 mmHg) induced a graded inhibition of O2-sensitive IK [IK(O2)] up to 46% at 0 mmHg. Moreover, hypoxia induced a 19-mV membrane depolarization and a twofold increase in cytosolic free Ca2+. In Ca(2+)-free condition, inhibition of IK(O2) induced an 8-mV depolarization, suggesting that inhibition of IK(O2) was responsible for initiating depolarization. The effect of reduced PO2 on the current-voltage relationship showed a reduction of outward current and a 14-mV shift in the reversal potential comparable with the amount of depolarization measured in current clamp experiments. Neither Ca(2+)-activated IK nor inwardly rectifying IK are responsible for the hypoxia-induced depolarization. In conclusion, PC-12 cells express an IK(O2), inhibition of which leads to membrane depolarization and increased intracellular Ca2+, making the PC-12 clonal cell line a useful model for studying the molecular and biophysical mechanisms that mediate O2 chemosensitivity.

Role of chloride currents in repolarizing rabbit atrial myocytes

1995 ◽  
Vol 268 (5) ◽  
pp. H1992-H2002 ◽  
Author(s):  
Z. Wang ◽  
B. Fermini ◽  
J. Feng ◽  
S. Nattel
Keyword(s):  
Action Potential ◽  
Reversal Potential ◽  
Outward Current ◽  
Cell Voltage ◽  
Disulfonic Acid ◽  
Transient Outward Current ◽  
Atrial Myocytes ◽  
Atrial Cells ◽  
K Current

Rabbit atrial cells manifest a prominent transient outward K+ current (Ito1), but this current recovers slowly from inactivation and is unlikely to be important at physiological rates (3-5 Hz). Depolarization of rabbit atrial cells also elicits a transient Ca(2+)-dependent outward Cl- current (Ito2). To compare the relative magnitude of these transient outward currents at various rates, we applied whole cell voltage-clamp techniques to isolated rabbit atrial myocytes. Whereas peak Ito1 exceeded Ito2 at slow rates (0.1 Hz), Ito1 was strongly reduced as rate was increased (by 97 +/- 2%, mean +/- SE, at 4 Hz), while Ito2 was slightly reduced (by 28 +/- 4%, 4 Hz). The reversal potential of transient outward tail currents at 0.07 Hz was -49 +/- 9 mV, while at 2.5 Hz the reversal potential became -18 +/- 7 mV (calculated Cl- reversal potential -18 mV). The addition of the Cl- transport blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 150 microM) or the replacement of external Cl- with methanesulfonate inhibited a large part of the transient outward current elicited by depolarization at 4 Hz. DIDS and Cl- replacement increased action potential duration in both single rabbit atrial cells and multicellular rabbit atrial preparations. We conclude that the Ca(2+)-dependent Cl- current is substantially larger than the transient K+ current at physiological rates in the rabbit and is likely to play a more important role in action potential repolarization than the latter current in this tissue in vivo.

scholarly journals Outward current in single smooth muscle cells of the guinea pig taenia coli.

1989 ◽  
Vol 93 (3) ◽  
pp. 551-564 ◽  
Author(s):  
Y Yamamoto ◽  
S L Hu ◽  
C Y Kao
Keyword(s):  
Guinea Pig ◽  
Time Constant ◽  
Time Course ◽  
Reversal Potential ◽  
Outward Current ◽  
Enzymatic Digestion ◽  
Taenia Coli ◽  
Physiological Conditions ◽  
Dependent Component ◽  
Voltage Dependent

In single myocytes of the guinea pig taenia coli, dispersed by enzymatic digestion, the late outward current is carried by K+. It has both a Ca2+-activated component and a voltage-dependent component which is resistant to external Co2+. The reversal potential is -84 mV, and the channel(s) for it are highly selective to K+. At 33 degrees C, the activation follows n2 kinetics, with a voltage-dependent time constant of 10.6 ms at 0 mV, which shortens to 1.7 ms at +70 mV. Deactivation follows a single-exponential time course, with a voltage-dependent time constant of 11 ms at -50 mV, which lengthens to 33 ms at -20 mV. During a 4.5-s maintained depolarization, IK inactivates, most of it into two exponential components, but there is a small noninactivating residue. It is surmised that during an action potential under physiological conditions, there is sufficient IK to cause repolarization.

scholarly journals The light-sensitive conductance of hyperpolarizing invertebrate photoreceptors: a patch-clamp study.

1994 ◽  
Vol 103 (6) ◽  
pp. 939-956 ◽  
Author(s):  
M P Gomez ◽  
E Nasi
Keyword(s):  
Single Channel ◽  
Light Stimulus ◽  
Divalent Cations ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Conductance ◽  
Resting Potential ◽  
Light Stimulation ◽  
Positive Direction ◽  
Single Channel Currents

Tight-seal recording was employed to investigate membrane currents in hyperpolarizing ciliary photoreceptors enzymatically isolated from the eyes of the file clam (Lima scabra) and the bay scallop (Pecten irradians). These two organisms are unusual in that their double retinas also possess a layer of depolarizing rhabdomeric cells. Ciliary photoreceptors from Lima have a rounded soma, 15-20 microns diam, and display a prominent bundle of fine processes up to 30 microns long. The cell body of scallop cells is similar in size, but the ciliary appendages are modified, forming small spherical structures that protrude from the cell. In both species light stimulation at a voltage near the resting potential gives rise to a graded outward current several hundred pA in amplitude, accompanied by an increase in membrane conductance. The reversal potential of the photocurrent is approximately -80 mV, and shifts in the positive direction by approximately 39 mV when the concentration of extracellular K is increased from 10 to 50 mM, consistent with the notion that light activates K-selective channels. The light-activated conductance increases with depolarization in the physiological range of membrane voltages (-30 to -70 mV). Such outward rectification is greatly reduced after removal of divalent cations from the superfusate. In Pecten, cell-attached recordings were also obtained; in some patches outwardly directed single-channel currents could be activated by light but not by voltage. The unitary conductance of these channels was approximately 26 pS. Solitary ciliary cells also gave evidence of the post stimulus rebound, which is presumably responsible for initiating the "off" discharge of action potentials at the termination of a light stimulus: in patches containing only voltage-dependent channels, light stimulation suppressed depolarization-induced activity, and was followed by a strong burst of openings, directly related to the intensity of the preceding photostimulation.

scholarly journals A novel action of quinine and quinidine on the membrane conductance of neurons from the vertebrate retina.

1994 ◽  
Vol 104 (6) ◽  
pp. 1039-1055 ◽  
Author(s):  
R P Malchow ◽  
H Qian ◽  
H Ripps
Keyword(s):  
Lucifer Yellow ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Conductance ◽  
Cobalt Acetate ◽  
Cinchona Alkaloids ◽  
Horizontal Cells ◽  
Patch Clamp Technique ◽  
Voltage Dependent ◽  
Gap Junctional

The cinchona alkaloids quinine and quinidine have been shown to block a broad range of voltage-gated membrane conductances in a variety of excitable tissues. Using the whole-cell version of the patch clamp technique, we examined the effects of these compounds on voltage-dependent currents from horizontal cells dissociated enzymatically from the all-rod retina of the skate. We report here a novel and unexpected action of quinine and quinidine on isolated horizontal cells. In addition to blocking several of the voltage-activated currents of these cells, the introduction of the alkaloids evoked a large outward current when the cells were held at depolarized potentials. Using tail current analysis, the reversal potential of the outward current was close to O mV, and the current was markedly suppressed by extracellularly applied cobalt, acetate, and halothane. Depolarization in the presence of quinine also permitted entry into the cells of extracellularly applied Lucifer yellow (MW = 443 D), whereas a 3-kD fluorescein-dextran complex was excluded. These findings suggest that the large, apparently nonselective conductance induced by quinine and quinidine results from the opening of hemi-gap junctional channels.

MCP-1 Enhances Excitability of Nociceptive Neurons in Chronically Compressed Dorsal Root Ganglia

2006 ◽  
Vol 96 (5) ◽  
pp. 2189-2199 ◽  
Author(s):  
J. H. Sun ◽  
B. Yang ◽  
D. F. Donnelly ◽  
C. Ma ◽  
R. H. LaMotte
Keyword(s):  
Dorsal Root ◽  
Reversal Potential ◽  
Outward Current ◽  
Peak Height ◽  
Resting Potential ◽  
Delayed Rectifier ◽  
Monocyte Chemoattractant Protein 1 ◽  
Nociceptive Neurons ◽  
Voltage Dependent ◽  
Ionic Mechanisms

Previous experimental results from our laboratory demonstrated that monocyte chemoattractant protein-1 (MCP-1) depolarizes or increases the excitability of nociceptive neurons in the intact dorsal root ganglion (DRG) after a chronic compression of the DRG (CCD), an injury that upregulates neuronal expression of both MCP-1 and mRNA for its receptor CCR2. We presently explore the ionic mechanisms underlying the excitatory effects of MCP-1. MCP-1 (100 nM) was applied, after CCD, to acutely dissociated small DRG neurons with nociceptive properties. Under current clamp, the proportion of neurons depolarized was similar to that previously observed for CCD-treated neurons in the intact ganglion, although the magnitude of depolarization was greater. MCP-1 induced a decrease in rheobase by 44 ± 10% and some cells became spontaneously active at resting potential. Action potential width at a voltage equal to 10% of the peak height was increased from 4.94 ± 0.23 to 5.90 ± 0.47 ms. In voltage clamp, MCP-1 induced an inward current in 27 of 50 neurons held at −60 mV, which increased with concentration over the range of 3 to 300 nM (EC50= 45 nM). The MCP-1–induced current was not voltage dependent and had an estimated reversal potential of −27 mV. In addition, MCP-1 inhibited a voltage-dependent, noninactivating outward current, presumably a delayed rectifier type K+conductance. We conclude that MCP-1 enhances excitability in CCD neurons by, at least, two mechanisms: 1) activation of a nonvoltage-dependent depolarizing current with characteristics similar to a nonselective cation conductance and 2) inhibition of a voltage-dependent outward current.

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