Na+, K+ and Ca2+ currents in identified leech neurones in culture

1989 ◽  
Vol 141 (1) ◽  
pp. 1-20
Author(s):  
R. R. Stewart ◽  
J. G. Nicholls ◽  
W. B. Adams
Keyword(s):  
Minor Component ◽  
Outward Current ◽  
Membrane Properties ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Channel Blockers ◽  
Sensory Neurones ◽  
K Current ◽  
The Individual ◽  
K Currents

1. Na+, K+ and Ca2+ currents have been measured by voltage-clamp in Retzius (R), anterior pagoda (AP) and sensory (pressure, touch and nociceptive) cells dissected from the central nervous system (CNS) of the leech. These cells maintain their distinctive membrane properties and action potential configurations in culture. Currents carried by the individual ions were analysed by the use of channel blockers and by their kinetics. Since the cells are isopotential they can be voltage-clamped effectively. 2. Depolarization, as expected, gave rise to an early inward Na+ current followed by a delayed outward K+ current. In Na+-free medium containing tetraethylammonium (TEA+), and in the presence of 4-aminopyridine (4-AP), inward Ca2+ currents were revealed that inactivated slowly and were blocked by Cd2+ and Mn2+. 3. Na+ and Ca2+ currents were similar in their characteristics in R. AP and sensory neurones. In contrast, K+ currents showed marked differences. Three principal K+ currents were identified. These differed in their time courses of activation and inactivation and in their responses to Ca2+ channel blockers. 4. K+ currents of the A-type (IA) activated and inactivated rapidly, were not affected by Ca2+ channel blockers and were eliminated by steady-state inactivation at holding potentials of −30 mV. A-type K+ currents were found in AP cells and as a minor component of the outward current in R cells. A Ca2+-activated K+ current (IC), that inactivated more slowly and was reduced by Ca2+ channel blockers, constituted the major outward current in R cells. The third K+ current resembled the delayed rectifier currents (IK1 and IK2) of squid axons with slow activation and inactivation kinetics. Such currents were found in R cells and in the sensory neurones (T, P and N). 5. The principal differences in membrane properties of identified leech neurones can be explained in terms of the numbers of Na+ channels and the distinctive kinetics of K+ channels in each type of cell.

Choline chloride activates time-dependent and time-independent K+ currents in dog atrial myocytes

1994 ◽  
Vol 266 (1) ◽  
pp. C42-C51 ◽  
Author(s):  
B. Fermini ◽  
S. Nattel
Keyword(s):  
Choline Chloride ◽  
Outward Current ◽  
Time Dependent ◽  
Equilibrium Potential ◽  
Delayed Rectifier ◽  
Atrial Myocytes ◽  
Patch Clamp Technique ◽  
Voltage Dependent ◽  
K Current ◽  
K Currents

Using the whole cell configuration of the patch-clamp technique, we studied the effect of isotonic replacement of bath sodium chloride (NaCl) by choline chloride (ChCl) in dog atrial myocytes. Our results show that ChCl triggered 1) activation of a time-independent background current, characterized by a shift of the holding current in the outward direction at potentials positive to the K+ equilibrium potential (EK), and 2) activation of a time- and voltage-dependent outward current, following depolarizing voltage steps positive to EK. Because the choline-induced current obtained by depolarizing steps exhibited properties similar to the delayed rectifier K+ current (IK), we named it IKCh. The amplitude of IKCh was determined by extracellular ChCl concentration, and this current was generally undetectable in the absence of ChCl. IKCh was not activated by acetylcholine (0.001-1.0 mM) or carbachol (10 microM) and could not be recorded in the absence of ChCl or when external NaCl was replaced by sucrose or tetramethylammonium chloride. IKCh was inhibited by atropine (0.01-1.0 microM) but not by the M1 antagonist pirenzepine (up to 10 microM). This current was carried mainly by K+ and was inhibited by CsCl (120 mM, in the pipette) or barium (1 mM, in the bath). We conclude that in dog atrial myocytes, ChCl activates a background conductance comparable to ACh-dependent K+ current, together with a time-dependent K+ current showing properties similar to IK.

Acetylcholine and caffeine activate Cl- and suppress K+ conductances in human bronchial smooth muscle

1996 ◽  
Vol 270 (5) ◽  
pp. L772-L781 ◽  
Author(s):  
L. J. Janssen
Keyword(s):  
Smooth Muscle ◽  
Reversal Potential ◽  
Outward Current ◽  
Mean Amplitude ◽  
Equilibrium Potential ◽  
Resting Membrane Potential ◽  
Delayed Rectifier ◽  
Positive Direction ◽  
K Current ◽  
K Currents

The conductance changes underlying agonist-evoked depolarization in human airway smooth muscle (ASM) were examined using single ASM cells liberated enzymatically from noncarcinomatous bronchi and studied using patch-clamp techniques. Step commands to potentials at or more positive than the resting membrane potential evoked outward current, which was predominantly delayed rectifier K+ current with some Ca(2+)-dependent K+ current Caffeine (5 mM) evoked depolarization and contraction lasting several minutes. During voltage clamp at -60 mV, caffeine evoked inward current with a latency of approximately equal to 1 s, mean amplitude of 320 +/- 65 pA, and a duration of approximately equal to 5 s (even though agonist application exceeded this duration). With the use of the perforated-path configuration, these responses could be evoked repeatedly at 4-min intervals for up to 30 min; rupture of the membrane and dialysis of the cytosol, however, abrogated the responses to caffeine. The current was outwardly rectifying with mean reversal potential (Vrev) of -31 +/- 4 mV. When K+ conductances were blocked by Ca+, the current-voltage (I-V) relationship was linear (i.e., an outwardly-rectifying component was eliminated) and Vrev was displaced in the positive direction to +2 +/- 1 mV. Changes in the CL- equilibrium potential were accompanied by a displacement of Vrev in a manner predicted by the Nernst equation for a Cl- current. The effects of caffeine were mimicked by acetylcholine; in addition, acetylcholine and caffeine each occluded the response to the other agonist. Spasmogens also caused a prolonged suppression of K+ currents (both Ca(2+)--dependent and delayed rectifier). We conclude that, in human ASM, acetylcholine and caffeine cause a transient activation of Ca(2+)--dependent Cl- current (due to release of internal Ca2+) and prolonged suppression of K+ currents, leading to depolarization and contraction.

Calcium-independent depolarization-activated potassium currents in superior colliculus-projecting rat visual cortical neurons

1995 ◽  
Vol 73 (6) ◽  
pp. 2163-2178 ◽  
Author(s):  
J. L. Albert ◽  
J. M. Nerbonne
Keyword(s):  
Superior Colliculus ◽  
Cortical Neurons ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Voltage Dependent ◽  
K Current ◽  
Current Densities ◽  
Visual Cortical ◽  
K Currents

1. K+ conductances were characterized in isolated, identified superior colliculus-projecting (SCP) rat visual cortical neurons. SCP neurons were identified in vitro under epifluorescence illumination after in vivo retrograde labeling with rhodamine-labeled microspheres or "beads." For experiments, SCP neurons were isolated from the primary visual cortex of postnatal day 7 to 16 (P7-P16) Long Evans rat pups after bead injections into the ipsilateral superior colliculus at p5. 2. Recording conditions were optimized to allow the characterization of Ca2+ -independent K+ conductances. SCP cells that were largely devoid of processes were selected for recording, and experiments were completed 2-30 h after cell isolation. Ca2+ -independent, depolarization-activated K+ currents were routinely recorded during 200-ms voltage steps to potentials positive to -50 mV from a holding potential of -70 mV. 3. Peak outward current densities and the relative amplitudes of the peak and plateau outward currents evoked during 200-ms voltage steps varied among SCP cells. Although cells were isolated from animals at different ages (P7-P16) and maintained for varying times in vitro (2-30 h), no correlations were found between the variations in peak current densities or peak to plateau current ratios and the age of the animal from which the cell was isolated or the length of time the cell was maintained in vitro before recording. 4. Pharmacological experiments revealed the coexpression of three K+ current components in SCP cells that could be separated on the basis of differing sensitivities to the K+ channel blockers, 4-aminopyridine (4-AP) and tetraethylammonium (TEA). Varying the concentration of 4-AP, for example, facilitated the separation of two rapidly activating K+ currents similar to A (IA) and D(ID) type currents in other cells. ID in SCP neurons is blocked by micromolar concentrations of 4-AP, whereas micromolar concentrations of 4-AP are required to effect complete block of IA in these cells. The current component remaining in the presence of high concentrations (5-10 mM) of 4-AP is slowly activating outward K+ current, similar to delayed rectifier (IK) currents in other cells. IK in SCP neurons is blocked by micromolar concentrations of TEA. 5. Activation of IA, ID, and IK in SCP neurons is voltage dependent, although the three current components display distinct time- and voltage-dependent properties. For example, although both IA and ID begin to activate at approximately -50 mV, IA activates two to three times faster than ID. In addition, the threshold for activation of IK (-30 mV) is approximately 20 mV depolarized from that of IA (or ID), and the voltage dependence of IK activation is steeper than that of IA and ID.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Suppression of the delayed rectifier type of voltage gated K+ outward current in megakaryocytes from patients with myelogenous leukemias

Blood ◽  
1995 ◽  
Vol 86 (3) ◽  
pp. 1043-1055 ◽  
Author(s):  
L Kapural ◽  
MB Feinstein ◽  
F O'Rourke ◽  
A Fein
Keyword(s):  
Outward Current ◽  
Myelogenous Leukemia ◽  
Delayed Rectifier ◽  
Contributory Factor ◽  
Voltage Gated ◽  
Acute Myelogenous ◽  
K Current ◽  
Malignant State ◽  
Erythroleukemia Cell ◽  
Normal Human

Abstract In normal human megakaryocytes, we identified a delayed rectifier type of voltage-gated outward K+ current (DRK). In two human megakaryoblastic tumor cell lines (DAMI, CHRF-288–11) and the human erythroleukemia cell line (HEL) the DRK current was not detected. To determine if the absence of the DRK current in the tumor cells is the result of the underlying malignant state, we examined megakaryocytes from myelogenous leukemia patients. In 24 of 29 megakaryocytes from the myelogenous leukemia patients, the DRK current was greatly suppressed, whereas in the remaining 5 megakaryocytes a normal large amplitude DRK current was present. We had the opportunity to reexamine megakaryocytes from a patient with acute promyelocytic leukemia (M3), after chemotherapy. Whereas the DRK current was suppressed before treatment, the current reappeared after chemotherapy. Exposure to the adenylate cyclase activator, forskolin, caused the appearance of a voltage-gated outward current in the megakaryocytes of patients with acute myelogenous leukemia. This finding suggests either that the channels underlying the DRK current are present but somehow suppressed in megakaryocytes from these patients or that forskolin induces a different voltage-gated outward current. We suggest that the megakaryocytes from the myelogenous leukemia patients with suppressed DRK current are abnormal, whereas the others may be normal megakaryocytes. The suppression of the DRK current may be a contributory factor to the dysregulation of thrombopoiesis (Zittoun et al: Semin Hop Paris 44:183, 1968 and Rabellino et al: Blood 63:615, 1984) in myelogenous leukemias.

Complexity of the outward K+ current of the rat megakaryocyte

1997 ◽  
Vol 272 (5) ◽  
pp. C1525-C1531 ◽  
Author(s):  
E. Romero ◽  
R. Sullivan
Keyword(s):  
K Channel ◽  
Delayed Rectifier ◽  
Channel Blockers ◽  
Excitable Cells ◽  
Electrophysiological Properties ◽  
Relative Contribution ◽  
Delayed Rectifier Current ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
K Current

Megakaryocytes isolated from rat bone marrow express a voltage-dependent, outward K+ current with complex kinetics of activation and inactivation. We found that this current could be separated into at least two components based on differential responses to K+ channel blockers. One component, which exhibited features of the "transient" or "A-type" K+ current of excitable cells, was more strongly blocked by 4-aminopyridine (4-AP) than by tetrabutylammonium (TBA). This current, which we designated as "4-AP-sensitive" current, activated rapidly at potentials more positive than -40 mV and subsequently underwent rapid voltage-dependent inactivation. A separate current that activated slowly was blocked much more effectively by TBA than by 4-AP. This "TBA-sensitive" component, which resembled a typical delayed rectifier current, was much more resistant to voltage-dependent inactivation. The relative contribution of each of these components varied from cell to cell. The effect of charybdotoxin was similar to that of 4-AP. Our data indicate that the voltage-dependent K+ current of resting megakaryocytes is more complex than heretofore believed and support the emerging concept that megakaryocytes possess intricate electrophysiological properties.

On the mechanism of modulation of transient outward current in cultured rat hippocampal neurons by di- and trivalent cations

1995 ◽  
Vol 73 (1) ◽  
pp. 73-79 ◽  
Author(s):  
G. Talukder ◽  
N. L. Harrison
Keyword(s):  
Metal Ions ◽  
Hippocampal Neurons ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Extracellular Medium ◽  
Bulk Surface ◽  
K Current ◽  
Trivalent Cations ◽  
High Concentrations

1. The mechanisms of Zn2+ modulation of transient outward current (TOC) were studied in cultured rat hippocampal neurons, using the voltage-clamp technique. In the presence of micromolar concentrations of external Zn2+, the voltage dependence of activation and inactivation was shifted to more positive membrane potentials. The gating of TOC was unaltered by internal application of Zn2+. The effect of Zn2+ were not mimicked by external Ca2+, except at very high concentrations (> 10 mM). 2. The modulatory effects of external Zn2+ on TOC gating were not reproduced, antagonized, nor enhanced by lowering external ionic strength, indicating that modulation by Zn2+ does not occur via screening of bulk surface negative charge. 3. A range of other divalent and trivalent metal ions also was studied, and several were found to modulate the transient outward current when added to the extracellular medium. In particular, Pb2+, La3+, and Gd3+ were potent modulators, showing activity in the low micromolar range. Other metal ions were weaker modulators (e.g., Cd2+) or were without activity at the concentrations tested (Fe3+, Cu2+, Ni2+). 4. The same range of ions also was tested on the delayed rectifier K+ current in cultured rat hippocampal neurons. None of the ions studied had significant effects on delayed rectifier gating, although high (> or = 100 microM) concentrations of Pb2+ and La3+ reduced maximal current amplitude, suggesting the possibility of channel block.(ABSTRACT TRUNCATED AT 250 WORDS)

Delayed rectifier K+ current in rabbit atrial myocytes

1995 ◽  
Vol 269 (2) ◽  
pp. H524-H532 ◽  
Author(s):  
K. Muraki ◽  
Y. Imaizumi ◽  
M. Watanabe ◽  
Y. Habuchi ◽  
W. R. Giles
Keyword(s):  
Maximum Amplitude ◽  
Outward Current ◽  
Cell Voltage ◽  
Inward Rectification ◽  
Resting Membrane Potential ◽  
Delayed Rectifier ◽  
Wave Form ◽  
Class Iii ◽  
Atrial Myocytes ◽  
K Current

The role of delayed rectifier K+ current(s) (IK) in rabbit left atrium was examined by applying the whole cell voltage-clamp technique to isolated single myocytes. Right-triangular waveforms, which mimic the shape of atrial action potentials (APs), and selective blockers were used to compare the contribution of IK with other K+ currents to repolarization of the APs. IK measured at 34 degrees C in atrial myocytes was very small; the maximum peak amplitude of the tail current (IK,tail) at -40 mV was approximately 50 pA. The IK,tail was almost abolished in most cells (approximately 80%) by the application of 1 microM E-4031, a class III antiarrhythmic drug. The E-4031-sensitive current recorded with the triangular command wave-form showed strong inward rectification and had a maximum amplitude of approximately 30 pA at -40 mV. Total outward current elicited by triangular command pulses depended strongly on stimulation frequency. The main frequency-dependent component was a Ca(2+)-independent transient K+ current (I(t)). I(t) elicited by triangular pulses at 1 Hz was substantially reduced by 4-aminopyridine (4-AP) at potentials positive to 0 mV but was not changed significantly by 1 microM E-4031; 100 microM E-4031 reduced I(t) by approximately 30%. The shape of the APs which were recorded from a single rabbit atrial cell strongly depended on the pulse frequency. Application of 1 microM E-4031 increased action potential duration (APD) in > 50% of cells examined but had little effect on the resting membrane potential (RMP). Application of 0.1 mM BaCl2 also lengthened APD and reduced RMP by approximately 20 mV.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous transient outward currents and delayed rectifier K+ current: effects of hypoxia

1998 ◽  
Vol 275 (1) ◽  
pp. L145-L154 ◽  
Author(s):  
C. Vandier ◽  
M. Delpech ◽  
P. Bonnet
Keyword(s):  
Steady State ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Outward Currents ◽  
K Current ◽  
The Mean ◽  
Patch Configuration ◽  
Spontaneous Transient Outward Currents ◽  
Dependent Mechanism

Single smooth muscle cells of rabbit intrapulmonary artery were voltage clamped using the perforated-patch configuration of the patch-clamp technique. We observed spontaneous transient outward currents (STOCs) and a steady-state outward current. Because STOCs were tetraethylammonium sensitive and activated by Ca2+ influx, they were believed to represent activation of Ca2+-activated K+ channels. The steady-state outward current, which was sensitive to 4-aminopyridine, was the delayed rectifier K+ current. In cells voltage clamped at 0 mV, we found that STOCs were not randomly distributed in amplitude but were composed of multiples of 1.57 ± 0.56 pA/pF. The mean frequency of STOCs was 5.51 ± 3.49 Hz. Ryanodine (10 μM), caffeine (5 mM), thapsigargin (200 nM), and hypoxia [Formula: see text] = 10 mmHg) decreased STOCs. The effect of hypoxia on STOCs was partially reversible only if the experiment was conducted in the presence of thapsigargin. Hypoxia and thapsigargin decrease steady-state outward current. Thapsigargin and removal of external Ca2+abolished the effect of hypoxia, suggesting that hypoxia decreases steady-state outward current by a Ca2+-dependent mechanism.

Segment-specific effects of FMRFamide on membrane properties of heart interneurons in the leech

1995 ◽  
Vol 74 (4) ◽  
pp. 1485-1497 ◽  
Author(s):  
J. Schmidt ◽  
S. Gramoll ◽  
R. L. Calabrese
Keyword(s):  
Outward Current ◽  
Membrane Conductance ◽  
Membrane Properties ◽  
Inward Current ◽  
Specific Effects ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
Conductance Increase

1. The effects of Phe-Met-Arg-Phe (FMRF)amide (10(-6) M) on membrane properties of heart interneurons in the third, fourth, and fifth segmental ganglia [HN(3), HN(4), and HN(5) cells, respectively] of the leech were studied using discontinuous current-clamp and single-electrode voltage-clamp techniques. FMRFamide was focally applied onto the soma of the cell under investigation. 2. Application of FMRFamide depolarized HN(3) and HN(4) cells by evoking an inward current. These responses were subject to pronounced desensitization. The inward currents evoked by application of FMRFamide were associated with an increase in membrane conductance and appeared to be voltage dependent. Currents were enhanced at more depolarized potentials. 3. The responsiveness of the HN(3) and HN(4) cells was not affected when the Ca2+ concentration in the bath saline was reduced from normal (1.8 mM) to 0.1 mM. The depolarizing response on application of FMRFamide was blocked when Co2+ was substituted for Ca2+. 4. HN(3) and HN(4) cells did not respond to FMRFamide application in Na(+)-free solution. Inward currents were largely reduced when bath saline with 30% of the normal Na+ concentration was used. When Li+ was substituted for Na+ in the saline, application of FMRFamide still evoked depolarizing responses in HN(3) and HN(4) cells. 5. We conclude that focal application of FMRFamide onto the somata of HN(3) and HN(4) cells evokes a voltage-dependent inward current, carried largely by Na+. 6. Focal application of FMRFamide onto somata of HN(5) cells hyperpolarized these cells by activating a voltage-dependent outward current. 7. HN(5) cells were loaded with Cl- until inhibitory postsynaptic potentials carried by Cl- reversed. Cl(-)-loaded cells still responded with a hyperpolarization when FMRFamide was applied onto their somata. Therefore the outward current evoked by FMRFamide appears to be mediated by a K+ conductance increase. 8. Application of FMRFamide onto the somata of HN(5) cells enhanced outward currents that were evoked by depolarizing voltage steps from a holding potential of -45 mV. 9. We conclude that the hyperpolarizing response of HN(5) cells to focal application of FMRFamide onto their somata is the result of an up-regulation of a voltage-dependent K+ current.

scholarly journals A time- and voltage-dependent K+ current in single cardiac cells from bullfrog atrium.

1986 ◽  
Vol 88 (6) ◽  
pp. 777-798 ◽  
Author(s):  
J R Hume ◽  
W Giles ◽  
K Robinson ◽  
E F Shibata ◽  
R D Nathan ◽  
...  
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Outward Current ◽  
Cardiac Cells ◽  
Delayed Rectifier ◽  
Mechanical Dispersion ◽  
Atrial Cells ◽  
Voltage Dependent ◽  
K Current ◽  
Kinetics Of

Individual myocytes were isolated from bullfrog atrium by enzymatic and mechanical dispersion, and a one-microelectrode voltage clamp was used to record the slow outward K+ currents. In normal [K+]o (2.5 mM), the slow outward current tails reverse between -95 and -100 mV. This finding, and the observed 51-mV shift of Erev/10-fold change in [K+]o, strongly suggest that the "delayed rectifier" in bullfrog atrial cells is a K+ current. This current, IK, plays an important role in initiating repolarization, and it is distinct from the quasi-instantaneous, inwardly rectifying background current, IK. In atrial cells, IK does not exhibit inactivation, and very long depolarizing clamp steps (20 s) can be applied without producing extracellular K+ accumulation. The possibility of [K+]o accumulation contributing to these slow outward current changes was assessed by (a) comparing reversal potentials measured after short (2 s) and very long (15 s) activating prepulses, and (b) studying the kinetics of IK at various holding potentials and after systematically altering [K+]o. In the absence of [K+]o accumulation, the steady state activation curve (n infinity) and fully activated current-voltage (I-V) relation can be obtained directly. The threshold of the n infinity curve is near -50 mV, and it approaches a maximum at +20 mV; the half-activation point is approximately -16 mV. The fully activated I-V curve of IK is approximately linear in the range -40 to +30 mV. Semilog plots of the current tails show that each tail is a single-exponential function, which suggests that only one Hodgkin-Huxley conductance underlies this slow outward current. Quantitative analysis of the time course of onset of IK and of the corresponding envelope of tails demonstrate that the activation variable, n, must be raised to the second power to fit the sigmoid onset accurately. The voltage dependence of the kinetics of IK was studied by recording and curve-fitting activating and deactivating (tail) currents. The resulting 1/tau n curve is U-shaped and somewhat asymmetric; IK exhibits strong voltage dependence in the diastolic range of potentials. Changes in the [Ca2+]o in the superfusing Ringer's, and/or addition of La3+ to block the transmembrane Ca2+ current, show that the time course and magnitude of IK are not significantly modulated by transmembrane Ca2+ movements, i.e., by ICa. These experimentally measured voltage- and time-dependent descriptors of IK strongly suggest an important functional role for IK in atrial tissue: it initiates repolarization and can be an important determinant of rate-induced changes in action potential duration.

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