scholarly journals Selective Inhibition of Transient K+ Current by La3+ in Crab Peptide-Secretory Neurons

1999 ◽  
Vol 81 (4) ◽  
pp. 1848-1855 ◽  
Author(s):  
Shumin Duan ◽  
Ian M. Cooke
Keyword(s):  
Divalent Cations ◽  
Outward Current ◽  
Selective Inhibition ◽  
Defined Medium ◽  
Neurosecretory Cells ◽  
Delayed Rectifier ◽  
Type Model ◽  
Time To Peak ◽  
Boltzmann Function ◽  
Secretory Neurons

Selective inhibition of transient K+ current by La3+ in crab peptide-secretory neurons. Although divalent cations and lanthides are well-known inhibitors of voltage-dependent Ca2+ currents ( I Ca), their ability to selectively inhibit a voltage-gated K+ current is less widely documented. We report that La3+ inhibits the transient K+current ( I A) of crab ( Cardisoma carnifex) neurosecretory cells at ED50 ∼5 μM, similar to that blocking I Ca, without effecting the delayed rectifier K+ current ( I K). Neurons were dissociated from the major crustacean neuroendocrine system, the X-organ-sinus gland, plated in defined medium, and recorded by whole cell patch clamp after 1–2 days in culture. The bath saline included 0.5 μM TTX and 0.5 mM CdCl2 to eliminate inward currents. Responses to depolarizing steps from a holding potential of −40 mV represented primarily I K. They were unchanged by La3+ up to 500 μM. Currents from −80 mV in the presence of 20 mM TEA were shown to represent primarily I A. La3+ (with TEA) reduced I A and maximum conductance ( G A) by ∼10% for 1 μM and another 10% each in 10 and 100 μM La3+. Normalized G A- V curves were well fit with a single Boltzmann function, with V 1/2 +4 mV and slope 15 mV in control; V 1/2 was successively ∼15 mV depolarized and slope increased ∼2 mV for each of these La3+ concentrations. Cd2+ (1 mM), Zn2+ (200 μM), and Pb2+ (100 μM) or removal of saline Mg2+ (26 mM) had little or no effect on I A. Steady-state inactivation showed similar right shifts (from V 1/2 −39 mV) and slope increases (from 2.5 mV) in 10 and 100 μM La3+. Time to peak I A was slowed in 10 and 100 μM La3+, whereas curves of normalized time constants of initial decay from peak I A versus V c were right-shifted successively ∼15 mV for the three La3+ concentrations. The observations were fitted by a Woodhull-type model postulating a La3+-selective site that lies 0.26–0.34 of the distance across the membrane electric field, and both block of K+ movement and interaction with voltage-gating mechanisms; block can be relieved by depolarization and/or outward current. The observation of selective inhibition of I A by micromolar La3+ raises concerns about its use in studies of I Ca to evaluate contamination by outward current.

Current- and Voltage-Clamp Recordings and Computer Simulations of Kenyon Cells in the Honeybee

2004 ◽  
Vol 92 (4) ◽  
pp. 2589-2603 ◽  
Author(s):  
Daniel G. Wüstenberg ◽  
Milena Boytcheva ◽  
Bernd Grünewald ◽  
John H. Byrne ◽  
Randolf Menzel ◽  
...  
Keyword(s):  
Voltage Clamp ◽  
Mushroom Body ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Insect Brain ◽  
Type Model ◽  
Kenyon Cells ◽  
Fast Transient

The mushroom body of the insect brain is an important locus for olfactory information processing and associative learning. The present study investigated the biophysical properties of Kenyon cells, which form the mushroom body. Current- and voltage-clamp analyses were performed on cultured Kenyon cells from honeybees. Current-clamp analyses indicated that Kenyon cells did not spike spontaneously in vitro. However, spikes could be elicited by current injection in approximately 85% of the cells. Of the cells that produced spikes during a 1-s depolarizing current pulse, approximately 60% exhibited repetitive spiking, whereas the remaining approximately 40% fired a single spike. Cells that spiked repetitively showed little frequency adaptation. However, spikes consistently became broader and smaller during repetitive activity. Voltage-clamp analyses characterized a fast transient Na+ current ( INa), a delayed rectifier K+ current ( IK,V), and a fast transient K+ current ( IK,A). Using the neurosimulator SNNAP, a Hodgkin–Huxley-type model was developed and used to investigate the roles of the different currents during spiking. The model led to the prediction of a slow transient outward current ( IK,ST) that was subsequently identified by reevaluating the voltage-clamp data. Simulations indicated that the primary currents that underlie spiking are INa and IK,V, whereas IK,A and IK,ST primarily determined the responsiveness of the model to stimuli such as constant or oscillatory injections of current.

scholarly journals Calcium currents in a fast-twitch skeletal muscle of the rat.

1983 ◽  
Vol 82 (4) ◽  
pp. 449-468 ◽  
Author(s):  
P L Donaldson ◽  
K G Beam
Keyword(s):  
Skeletal Muscle ◽  
Leakage Current ◽  
Calcium Current ◽  
Outward Current ◽  
Extracellular Calcium ◽  
Calcium Currents ◽  
Slow Inward Current ◽  
Delayed Rectifier ◽  
Inward Current ◽  
Time To Peak

Slow ionic currents were measured in the rat omohyoid muscle with the three-microelectrode voltage-clamp technique. Sodium and delayed rectifier potassium currents were blocked pharmacologically. Under these conditions, depolarizing test pulses elicited an early outward current, followed by a transient slow inward current, followed in turn by a late outward current. The early outward current appeared to be a residual delayed rectifier current. The slow inward current was identified as a calcium current on the basis that (a) its magnitude depended on extracellular calcium concentration, (b) it was blocked by the addition of the divalent cations cadmium or nickel, and reduced in magnitude by the addition of manganese or cobalt, and (c) barium was able to replace calcium as an inward current carrier. The threshold potential for inward calcium current was around -20 mV in 10mM extracellular calcium and about -35 mV in 2 mM calcium. Currents were net inward over part of their time course for potentials up to at least +30 mV. At temperatures of 20-26 degrees C, the peak inward current (at approximately 0 mV) was 139 +/- 14 microA/cm2 (mean +/- SD), increasing to 226 +/- 28 microA/cm2 at temperatures of 27-37 degrees C. The late outward current exhibited considerable fiber-to-fiber variability. In some fibers it was primarily a time-independent, nonlinear leakage current. In other fibers it was primarily a time-independent, nonlinear leakage current. In other fibers it appeared to be the sum of both leak and a slowly activated outward current. The rate of activation of inward calcium current was strongly temperature dependent. For example, in a representative fiber, the time-to-peak inward current for a +10-mV test pulse decreased from approximately 250 ms at 20 degrees C to 100 ms at 30 degrees C. At 37 degrees C, the time-to-peak current was typically approximately 25 ms. The earliest phase of activation was difficult to quantify because the ionic current was partially obscured by nonlinear charge movement. Nonetheless, at physiological temperatures, the rate of calcium channel activation in rat skeletal muscle is about five times faster than activation of calcium channels in frog muscle. This pathway may be an important source of calcium entry in mammalian muscle.

Ionic currents of morphologically distinct peptidergic neurons in defined culture

1992 ◽  
Vol 67 (5) ◽  
pp. 1301-1315 ◽  
Author(s):  
D. E. Meyers ◽  
R. A. Graf ◽  
I. M. Cooke
Keyword(s):  
Outward Current ◽  
Ionic Currents ◽  
Cell Types ◽  
Defined Medium ◽  
Neurosecretory System ◽  
Ca Current ◽  
Patch Clamp Technique ◽  
Time To Peak ◽  
The Mean ◽  
Defined Culture

1. The X-organ sinus gland is a major peptidergic neurosecretory system in Crustacea, analogous to the vertebrate hypothalamoneurohypophyseal system. Neuronal somata isolated from the crab (Cardisoma carnifex) X-organ and maintained in primary culture in unconditioned, fully defined medium show immediate regenerative outgrowth. Outgrowth occurring as broad lamellipodia ("veiled") distinguishes neurons consistently showing crustacean hyperglycemic hormone immunoreactivity. Neurons that are immunoreactive against molt-inhibiting hormone and red pigment concentrating hormone antisera give rise to branched neurites ("branched"). 2. The whole-cell variation of the patch-clamp technique was used to study the electrophysiology of these two cell types 24-48 h after plating. Under current clamp, only veiled neurons fired overshooting action potentials either spontaneously or in response to depolarization. 3. Under voltage clamp, net current was predominantly outward. When solutions that suppressed outward current were used, only veiled neurons showed significant inward current. These included a tetrodotoxin (TTX)-sensitive Na current and a slow (time to peak 6-10 ms at 0 mV) Cd-sensitive Ca current (ICa) that was activated at potentials less than -30 mV, was maximal at 0 to +20 mV, and did not reverse at potentials up to +60 mV. 4. In TTX, the form of the Ca current I(V) curve was unchanged by changes of holding potential between -40 and -80 mV, and 75-100% of ICa was available from -40 mV. 5. ICa inactivated slowly and incompletely. Analysis with two-pulse regimes suggested that both inactivation and facilitation mechanisms were present. 6. Outward current was examined in the presence and absence of 0.5 mM Cd2+ (1 microM TTX was always present in the external medium). Cd2+ ions slightly reduced the peak outward current, usually by less than 10% (Vc = -10 to +20 mV; Vh = -80 mV). All additional observations were in the presence of TTX and Cd2+. 7. Both cell types expressed a 4-aminopyridine (4-AP)-sensitive transient current, analogous to IA, and a slower-rising (minimum time to peak 20 ms), sustained current that was partially sensitive to tetraethylammonium, analogous to IK. 8. The mean Vh at which IA was half inactivated was -46 mV, and the mean time constant for removal of inactivation was 46 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

A Slow Transient Potassium Current Expressed in a Subset of Neurosecretory Neurons of the Hypothalamic Paraventricular Nucleus

2000 ◽  
Vol 84 (4) ◽  
pp. 1814-1825 ◽  
Author(s):  
Jason A. Luther ◽  
Katalin Cs. Halmos ◽  
Jeffrey G. Tasker
Keyword(s):  
Paraventricular Nucleus ◽  
Potassium Current ◽  
Outward Current ◽  
Retrograde Transport ◽  
Neurosecretory Cells ◽  
Firing Frequency ◽  
Hypothalamic Paraventricular Nucleus ◽  
Transient Outward Current ◽  
Type I ◽  
Double Labeling

Type I putative magnocellular neurosecretory cells of the hypothalamic paraventricular nucleus (PVN) express a prominent transient outward rectification generated by an A-type potassium current. Described here is a slow transient outward current that alters cell excitability and firing frequency in a subset of type I PVN neurons (38%). Unlike most of the type I neurons (62%), the transient outward current in these cells was composed of two kinetically separable current components, a fast activating, fast inactivating component, resembling an A-type potassium current, and a slowly activating [10–90% rise time: 20.4 ± 12.8 (SE) ms], slowly inactivating component (time constant of inactivation: τ = 239.0 ± 66.1 ms). The voltage dependence of activation and inactivation and the sensitivity to block by 4-aminopyridine (5 mM) and tetraethylammonium chloride (10 mM) of the fast and slow components were similar. Compared to the other type I neurons, the neurons that expressed the slow transient outward current were less excitable when hyperpolarized, requiring larger current injections to elicit an action potential (58.5 ± 13.2 vs. 15.4 ± 2.4 pA; 250-ms duration; P < 0.01), displaying a longer delay to the first spike (184.9 ± 15.7 vs. 89.7 ± 8.8 ms with 250- to 1,000-ms, 50-pA current pulses; P < 0.01), and firing at a lower frequency (18.7 ± 4.6 vs. 37.0 ± 5.5 Hz with 100-pA current injections; P < 0.05). These data suggest that a distinct subset of type I PVN neurons express a novel slow transient outward current that leads to a lower excitability. Based on double labeling following retrograde transport of systemically administered fluoro-gold and intracellular injection of biocytin, these cells are neurosecretory and are similar morphologically to magnocellular neurosecretory cells, although it remains to be determined whether they are magnocellular neurons.

Characterization and functional consequences of delayed rectifier current transient in ventricular repolarization

2000 ◽  
Vol 278 (3) ◽  
pp. H806-H817 ◽  
Author(s):  
Gary A. Gintant
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Inward Rectifier ◽  
Ventricular Repolarization ◽  
Delayed Rectifier ◽  
Voltage Range ◽  
Delayed Rectifier Current ◽  
Recovery From Inactivation ◽  
Voltage Dependent

Although inactivation of the rapidly activating delayed rectifier current ( I Kr) limits outward current on depolarization, the role of I Kr (and recovery from inactivation) during repolarization is uncertain. To characterize I Krduring ventricular repolarization (and compare with the inward rectifier current, I K1), voltage-clamp waveforms simulating the action potential were applied to canine ventricular, atrial, and Purkinje myocytes. In ventricular myocytes, I Kr was minimal at plateau potentials but transiently increased during repolarizing ramps. The I Kr transient was unaffected by repolarization rate and maximal after 150-ms depolarizations (+25 mV). Action potential clamps revealed the I Kr transient terminating the plateau. Although peak I Kr transient density was relatively uniform among myocytes, potentials characterizing the peak transients were widely dispersed. In contrast, peak inward rectifier current ( I K1) density during repolarization was dispersed, whereas potentials characterizing I K1 defined a narrower (more negative) voltage range. In summary, rapidly activating I Kr provides a delayed voltage-dependent (and functionally time-independent) outward transient during ventricular repolarization, consistent with rapid recovery from inactivation. The heterogeneous voltage dependence of I Kr provides a novel means for modulating the contribution of this current during repolarization.

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.

Modulation of the delayed rectifier, IK, by cadmium in cat ventricular myocytes

1992 ◽  
Vol 262 (1) ◽  
pp. C75-C83 ◽  
Author(s):  
C. H. Follmer ◽  
N. J. Lodge ◽  
C. A. Cullinan ◽  
T. J. Colatsky
Keyword(s):  
Voltage Clamp ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Membrane Potentials ◽  
Delayed Rectifier ◽  
Voltage Range ◽  
Control Value ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Slope Factor

The effects of cadmium on the delayed outward potassium current (IK) were investigated in isolated cat ventricular myocytes using the single suction pipette voltage-clamp technique. IK activation was examined using peak tail currents elicited after 750-ms voltage-clamp steps to selected membrane potentials from a holding potential of -40 mV. In the presence of Cd2+ (0.2 mM), peak tail currents increased from a control value of 85 +/- 12 to 125 +/- 18 pA (n = 4). Activation curves constructed from the average peak tail-current measurements in all experiments showed that Cd2+ shifted the voltage dependence of activation to more positive potentials by 16.4 +/- 2.0 mV and increased the slope factor of the activation curve from 6.1 +/- 0.2 to 6.9 +/- 0.2 mV. In the absence of Cd2+, increases in holding potential from -30 to -70 mV had no effect on the magnitude of the peak tail currents, suggesting that the Cd(2+)-induced increase was not the result of a voltage-dependent increase in the number of available K+ channels at the holding potential. Slow voltage ramps from -70 to +70 mV revealed that Cd2+ increased the outward current at membrane potentials positive to +20 mV and shifted the voltage range in which IK inwardly rectified to more positive potentials. The fully activated current-voltage relationship was also shifted to more positive potentials by Cd2+. Cd2+ did not alter channel selectivity for K+.(ABSTRACT TRUNCATED AT 250 WORDS)

Separation and identification of multiple potassium currents regulating the pacemaker activity of insect neurosecretory cells (DUM neurons)

1995 ◽  
Vol 73 (1) ◽  
pp. 160-171 ◽  
Author(s):  
F. Grolleau ◽  
B. Lapied
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Outward Current ◽  
Potassium Currents ◽  
Neurosecretory Cells ◽  
Transient Current ◽  
Pacemaker Activity ◽  
Dum Neurons ◽  
K Current ◽  
A Current

1. Whole cell voltage-clamp studies performed in isolated adult neurosecretory cells identified as dorsal unpaired median (DUM) neurons of the terminal abdominal ganglion of the cockroach Periplaneta americana have allowed us to reveal a complex voltage-dependent outward current regulating the pacemaker activity. 2. The global outward current remaining after tetrodotoxin treatment was activated by depolarization above -50 mV, showing steep voltage dependence and outward rectification. 3. We used tail current analysis to determine the ionic selectivity of this outward current. The reversal potentials for two extracellular potassium concentrations (-92.7 and -65.4 mV for 3.1 and 10 mM, respectively) is consistent with the expected equilibrium potential for potassium ions. 4. Both peak and sustained components of the global outward K+ current were reduced by external application of 20 mM tetraethylammonium chloride, 10 nM iberiotoxin, 1 nM charybdotoxin (CTX) and 1 mM cadmium chloride. Subtraction of current recorded in CTX solution from that in control solution revealed an unusual biphasic Ca(2+)-dependent K+ current. The fast transient current resistant to 5 mM 4-aminopyridine (4-AP) is distinguished by its dependence on holding potential and time course from the late sustained current. 5. In addition, two other components of CTX-resistant outward K+ current could be separated by sensitivity to 4-AP, time course, and voltage dependence. Beside a calcium-independent delayed outwardly rectifying current, a 4-AP-sensitive fast transient current resembling the A-current has been also identified. It activates at negative potential (about -65 mV) and unlike the A-current of other neurons, it inactivates rapidly with complex inactivation kinetics. A-like current is half-inactivated at -63.5 mV and half-activated at -35.6 mV. 6. Our findings demonstrate for the first time in DUM neuron cell bodies the existence of multiple potassium currents underlying the spontaneous electrical activity. Their identification and characterization represent a fundamental step in further understanding the pacemaker properties of these insect neurosecretory cells.

Transient potassium currents in avian sensory neurons

1990 ◽  
Vol 63 (4) ◽  
pp. 725-737 ◽  
Author(s):  
S. K. Florio ◽  
C. D. Westbrook ◽  
M. R. Vasko ◽  
R. J. Bauer ◽  
J. L. Kenyon
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Potassium Currents ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Small Component ◽  
Whole Cell ◽  
Outward Currents

1. We used the patch-clamp technique to study voltage-activated transient potassium currents in freshly dispersed and cultured chick dorsal root ganglion (DRG) cells. Whole-cell and cell-attached patch currents were recorded under conditions appropriate for recording potassium currents. 2. In whole-cell experiments, 100-ms depolarizations from normal resting potentials (-50 to -70 mV) elicited sustained outward currents that inactivated over a time scale of seconds. We attribute this behavior to a component of delayed rectifier current. After conditioning hyperpolarizations to potentials negative to -80 mV, depolarizations elicited transient outward current components that inactivated with time constants in the range of 8-26 ms. We attribute this behavior to a transient outward current component. 3. Conditioning hyperpolarizations increased the rate of activation of the net outward current implying that the removal of inactivation of the transient outward current allows it to contribute to early outward current during depolarizations from negative potentials. 4. Transient current was more prominent on the day the cells were dispersed and decreased with time in culture. 5. In cell-attached patches, single channels mediating outward currents were observed that were inactive at resting potentials but were active transiently during depolarizations to potentials positive to -30 mV. The probability of channels being open increased rapidly (peaking within approximately 6 ms) and then declined with a time constant in the range of 13-30 ms. With sodium as the main extracellular cation, single-channel conductances ranged from 18 to 32 pS. With potassium as the main extracellular cation, the single-channel conductance was approximately 43 pS, and the channel current reversed near 0 mV, as expected for a potassium current. 6. We conclude that the transient potassium channels mediate the component of transient outward current seen in the whole-cell experiments. This current is a relatively small component of the net current during depolarizations from normal resting potentials, but it can contribute significant outward current early in depolarizations from hyperpolarized potentials.

Sign in / Sign up

Export Citation Format

Share Document