scholarly journals Unitary K+ Currents in Growth Cones and Perikaryon of Identified Helix Neurones in Culture

1990 ◽  
Vol 149 (1) ◽  
pp. 79-94
Author(s):  
K. A. GREEN ◽  
G. B. POWELL ◽  
A. COTTRELL
Keyword(s):  
Growth Cones ◽  
Resting Potential ◽  
Channel Block ◽  
Sensory Neurones ◽  
K Channels ◽  
K Current ◽  
The Mean ◽  
K Concentration ◽  
K Currents

Unitary potassium (K+) currents of several different conductances have been recorded from the growth cones of isolated Cl neurones from Helix aspersa. The isolated neurones were maintained in culture for up to 1 week. Similar unitary currents were recorded in the growth cones of other isolated Helix neurones. The activity of one type of unitary K+ current recorded from the growth cones of the Cl neurone and other neurones was very similar to that described for the S-channel of the perikarya of Aplysia sensory neurones. Another type of unitary K+ current showed fast flickering and reduced amplitude when the membrane was held at large positive potentials, which is suggestive of channel block by some agent. The conductances of the K+ channels in the growth cones of isolated Cl neurones were generally smaller than those recorded in this and in previous studies from the perikarya of Cl neurones in situ. However, unitary K+ currents recorded from the perikaryon of the Cl neurone, and from other identified neurones, in culture also had lower conductances than those recorded in situ. The mean resting potential of the isolated neurones was smaller than those from neurones in situ. This and other results suggested that reduced intracellular K+ concentration in the isolated neurones might be an important factor in deciding the conductance of the recorded channels.

scholarly journals Gonadotropin-Releasing Hormone Inhibits Ether-à-Go-Go-Related Gene K+ Currents in Mouse Gonadotropes

Endocrinology ◽  
2010 ◽  
Vol 151 (3) ◽  
pp. 1079-1088 ◽  
Author(s):  
Wiebke Hirdes ◽  
Crenguta Dinu ◽  
Christiane K. Bauer ◽  
Ulrich Boehm ◽  
Jürgen R. Schwarz
Keyword(s):  
Resting Potential ◽  
Related Gene ◽  
Activation Curve ◽  
Signal Cascade ◽  
Primary Mouse ◽  
Voltage Dependent ◽  
K Current ◽  
Unknown Signal ◽  
Ca2 Channels ◽  
K Currents

Secretion of LH from gonadotropes is initiated by a GnRH-induced increase in intracellular Ca2+ concentration ([Ca2+]i). This increase in [Ca2+]i is the result of Ca2+ release from intracellular stores and Ca2+ influx through voltage-dependent Ca2+ channels. Here we describe an ether-à-go-go-related gene (erg) K+ current in primary mouse gonadotropes and its possible function in the control of Ca2+ influx. To detect gonadotropes, we used a knock-in mouse strain, in which GnRH receptor-expressing cells are fluorescently labeled. Erg K+ currents were recorded in 80–90% of gonadotropes. Blockage of erg currents by E-4031 depolarized the resting potential by 5–8 mV and led to an increase in [Ca2+]i, which was abolished by nifedipine. GnRH inhibited erg currents by a reduction of the maximal erg current and in some cells additionally by a shift of the activation curve to more positive potentials. In conclusion, the erg current contributes to the maintenance of the resting potential in gonadotropes, thereby securing a low [Ca2+]i by restricting Ca2+ influx. In addition, the erg channels are modulated by GnRH by an as-yet unknown signal cascade.

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 possible role of inwardly rectifying K+ channels in chick myoblast differentiation

1997 ◽  
Vol 272 (3) ◽  
pp. C894-C900 ◽  
Author(s):  
K. S. Shin ◽  
J. Y. Park ◽  
H. Kwon ◽  
C. H. Chung ◽  
M. S. Kang
Keyword(s):  
Time Course ◽  
Developmental Change ◽  
Myoblast Differentiation ◽  
Resting Membrane Potential ◽  
K Channels ◽  
K Concentration ◽  
Inwardly Rectifying ◽  
K Permeability ◽  
K Currents

We examined the developmental change of inwardly rectifying K+ channels (IRK) and its possible role in myogenesis. Northern blot analysis revealed an increase in the level of IRK mRNA during myogenesis. Accordingly, IRK current was not detectable in replicating myoblasts but first appeared in aligned myoblasts that were competent for fusion and gradually increased thereafter. The time course change of IRK activity was closely related to the increase in resting membrane potential during myogenesis. Application of 0.5 mM Ba2+ to the bath depolarized the membrane and blocked IRK currents dramatically but not outwardly rectifying K+ currents. Myoblasts devoid of IRK had low resting K+ permeability, whereas myotubes that possess IRK had high resting K+ permeability. In some aligned myoblasts, anomalous hyperpolarization was elicited by increasing extracellular K+ concentration, which may be attributable to the increased conductance of IRK. Noteworthy was the fact that maximal fusion was obtained at this range of K+ concentration. These findings imply that IRK is responsible for the change in the K+ permeability during chick myogenesis, which may provide a larger driving force for Ca2+ influx that is a prerequisite for myoblast fusion.

Distribution of Na+ and K+ Currents in Soma, Axons and Growth Cones of Leech Retzius Neurones in Culture

1990 ◽  
Vol 150 (1) ◽  
pp. 1-17 ◽  
Author(s):  
U. GARCÍA ◽  
S. GRUMBACHER-REINERT ◽  
R. BOOKMAN ◽  
H. REUTER
Keyword(s):  
Cultured Cells ◽  
Growth Cones ◽  
Proximal Segment ◽  
Mapping Procedure ◽  
Na Currents ◽  
K Current ◽  
Current Densities ◽  
A New Technique ◽  
Retzius Cells ◽  
K Currents

1. Leech Retzius neurones were isolated by a new technique which allowed investigation of macroscopic currents over the surface of the cell body and the axons using loose patch-clamp. The distribution of ion current densities was measured for neurones that had just been removed from the CNS, and for cultured cells in which neurite outgrowth had begun. To standardize the mapping procedure, the same patch electrode was used at various sites along the neurone. 2. Immediately after isolation of the cell, rapidly activating and inactivating Na+ currents were recorded from distal segments of the axons, but not from the soma or the proximal segment. Na+ currents were isolated by using patch electrodes containing tetraethylammonium (TEA+) and 4-aminopyridine (4-AP) to block K+ channels and Cd2+ to block calcium channels. Na+ currents in all regions of the neurone where they could be recorded were similar in their voltage dependence and kinetics. The Na+ current density was highest at the broken tips of the axon stumps. 3. Neurites began to extend from the broken axon tips approximately 30min after isolation. Newly grown processes showed a high density of Na+ currents at their growth cones. After 2 days in culture the current densities became more uniformly distributed and Na+ currents could then be recorded in the soma and proximal axon segments. 4. In agreement with earlier studies made with conventional two-electrode voltage-clamp, three principal K+ currents were detected in Retzius cells: a rapidly activating and inactivatingA-type current blocked by 4-AP (IA); a more slowly activating and inactivating delayed K+ current blocked by TEA+ (IK1); and a Ca2+-activated K+ current (IC). Immediately after isolation of the Retzius cell, both rapid A-type and slow delayed K+ currents were distributed more uniformly than Na+ currents over the soma and axons. In their voltage sensitivities and kinetics, these two K+ currents were markedly different from each other; their characteristics were, however, constant in different regions of the cell. 5. Ca2+ currents were too small to be measured directly during depolarizing pulses. However, tail currents were large enough to demonstrate the presence of Ca2+ channels in the proximal segment of the axon and in the soma; the currents were not sufficiently large to resolve their spatial distribution. 6. It is concluded that ion channels are present in newly grown membranes and that the density of Na+ channels is highest in the tips of distal axon stumps from which outgrowth begins. By contrast, K+ currents are distributed more uniformly along the neurone.

Norepinephrine selectively reduces slow Ca2+- and Na+-mediated K+ currents in cat neocortical neurons

1989 ◽  
Vol 61 (2) ◽  
pp. 245-256 ◽  
Author(s):  
R. C. Foehring ◽  
P. C. Schwindt ◽  
W. E. Crill
Keyword(s):  
Firing Rate ◽  
Voltage Clamp ◽  
Resting Potential ◽  
Constant Current ◽  
Repetitive Firing ◽  
Slow Phase ◽  
Voltage Dependent ◽  
Constant Current Stimulation ◽  
K Current ◽  
K Currents

1. The effects of norepinephrine (NE) and related agonists and antagonists were examined on large neurons from layer V of cat sensorimotor cortex ("Betz cells") were examined in a brain slice preparation using intracellular recording, constant current stimulation and single microelectrode voltage clamp. 2. Application of NE (0.1-100 microM) usually caused a small depolarization from resting potential; hyperpolarizations were rare. Application of NE reversibly reduced rheobase and both the Ca2+- and Na+-dependent portions of the slow afterhyperpolarization (sAHP) that followed sustained firing evoked by constant current injection. The faster Ca2+-dependent medium afterhyperpolarization (mAHP), the fast afterhyperpolarization (fAHP), the action potential, and input resistance were unaffected. 3. The changes in excitability produced by NE application were most apparent during prolonged stimulation. The cells exhibited steady repetitive firing to currents that were formerly ineffective. The slow phase of spike frequency adaptation was reduced selectively and less habituation occurred during repeated long-lasting stimuli. The relation between firing rate and injected current became steeper if firing rate was averaged over several hundred milliseconds. 4. During voltage clamp in TTX, NE application selectively reduced the slow component of Ca2+-mediated K+ current. The faster Ca2+-mediated K+ current was unaffected, as were two voltage-dependent, transient K+ currents, the anomalous rectifier and leakage conductance measured at resting potential. Depolarizing voltage steps in the presence of Cd2+ revealed an apparent time- and voltage-dependent increase of the persistent Na+ current after NE application. The voltage-clamp results suggested ionic mechanisms for all effects seen during constant current stimulation except the depolarization from resting potential. The latter was insensitive to Cd2+ and TTX and occurred without a detectable change in membrane conductance. 5. NE application did not alter Ca2+ spikes evoked in the presence of TTX and 10 mM TEA. Inward Ca2+ currents examined during voltage clamp in TTX (with K+ currents reduced) became slightly larger after NE application. We conclude that NEs reduction of the slow Ca2+-mediated K+ current is not caused by reduction of Ca2+ influx. 6. Effects on membrane potential, rheobase, and the sAHP were mimicked by the beta-adrenergic agonist isoproterenol, but not by the alpha-adrenergic agonists clonidine or phenylephrine at higher concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

The ionic mechanism of the slow outward current in Aplysia neurons

1985 ◽  
Vol 54 (2) ◽  
pp. 449-461 ◽  
Author(s):  
J. R. Huguenard ◽  
K. L. Zbicz ◽  
D. V. Lewis ◽  
G. J. Evans ◽  
W. A. Wilson
Keyword(s):  
Reversal Potential ◽  
Outward Current ◽  
Membrane Conductance ◽  
Ion Concentration ◽  
Equilibrium Potential ◽  
Potassium Efflux ◽  
Aplysia Neurons ◽  
K Current ◽  
K Concentration ◽  
K Currents

A slow outward current associated with spike frequency adaptation has been studied in the giant Aplysia neurons R2 and LP1. The current was observed during 60-s voltage clamp commands to potentials just below spike threshold. The slow outward current shows a marked voltage dependence at membrane potential less negative than -40 mV. The slow outward current is associated with increased membrane conductance. The K+ sensitivity of the slow outward current was studied by varying the extracellular K+ concentration and also by measuring potassium efflux with a K+-sensitive electrode. Both procedures indicated that the slow outward current was K+ dependent. Tail currents following the activation of the slow outward current were examined. They were shown to have a similar potassium sensitivity as the slow outward current and had a reversal potential near the potassium equilibrium potential for these cells. The sensitivity of the slow outward current to known blockers of K+ currents, tetraethylammonium and 4-aminopyridine, was tested. The sensitivity was much less than that reported for other K+ currents. The sensitivity of the slow outward current to changes of the extracellular concentrations of Na+ and Cl- ions, as well as electrogenic pump inhibitors, was tested. The results indicate that the slow outward current is much less sensitive to these changes than to the manipulations of the extracellular K+ ion concentration. We tested the sensitivity of this current to manipulations of intracellular and extracellular Ca2+ ion concentrations. We found that the current persisted at a slightly reduced level in the absence of extracellular calcium or in the presence of calcium blocking agents, cobalt and lanthanum. Intracellular injection of the calcium chelator EGTA at a concentration sufficient to block the Ca2+-dependent K+ current, seen after a brief (1.4-s) burst of action potentials, had minimal effects on the slow outward current. Procedures thought to increase intracellular Ca2+ were tested. We found that exposure of the cell to solutions containing elevated Ca2+ concentrations for prolonged periods increased the slow outward current. Also, treatment with drugs thought to elevate intracellular Ca2+ increased the slow outward current. In conclusion, the slow outward current results from an increased K+ conductance.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Light-dependent K+ Channels in the Mollusc Onchidium Simple Photoreceptors Are Opened by cGMP

2002 ◽  
Vol 120 (4) ◽  
pp. 581-597 ◽  
Author(s):  
Tsukasa Gotow ◽  
Takako Nishi
Keyword(s):  
K Channel ◽  
Single Channels ◽  
Open Probability ◽  
Mean Values ◽  
K Channels ◽  
Open Time ◽  
Hyperpolarizing Response ◽  
The Mean ◽  
K Concentration ◽  
Inside Out

Light-dependent K+ channels underlying a hyperpolarizing response of one extraocular (simple) photoreceptor, Ip-2 cell, in the marine mollusc Onchidium ganglion were examined using cell-attached and inside-out patch-clamp techniques. A previous report (Gotow, T., T. Nishi, and H. Kijima. 1994. Brain Res. 662:268–272) showed that a depolarizing response of the other simple photoreceptor, A-P-1 cell, results from closing of the light-dependent K+ channels that are activated by cGMP. In the cell-attached patch recordings of Ip-2 cells, external artificial seawater (ASW) was replaced with a modified ASW containing 150 mM K+ and 200 mM Mg2+ to suppress any synaptic input and to maintain the membrane potential constant. When Ip-2 cells were equilibrated with this modified ASW, the internal K+ concentration was estimated to be 260 mM. Light-dependent single-channels in the cell-attached patch on these cells were opened by light but scarcely by voltage. After confirming the light-dependent channel activity in the cell-attached patches, an application of cGMP to the excised inside-out patches newly activated a channel that disappeared on removal of cGMP. Open and closed time distributions of this cGMP-activated channel could be described by the sum of two exponents with time constants τo1, τo2 and τc1, τc2, respectively, similar to those of the light-dependent channel. In both the channels, τo1 and τo2 in ms ranges were similar to each other, although τc2 over tens of millisecond ranges was different. τo1, τo2, and the mean open time τo were both independent of light intensity, cGMP concentration, and voltage. In both channels, the open probability increased as the membrane was depolarized, without changing any of τo2 or τo. In both, the reversal potentials using 200- and 450-mM K+-filled pipettes were close to the K+ equilibrium potentials, suggesting that both the channels are primarily K+ selective. Both the mean values of the channel conductance were estimated to be the same at 62 and 91 pS in 200- and 450-mM K+ pipettes at nearly 0 mV, respectively. Combining these findings with those in the above former report, it is concluded that cGMP is a second messenger which opens the light-dependent K+ channel of Ip-2 to cause hyperpolarization, and that the channel is the same as that of A-P-1 closed by light.

scholarly journals Inhibition of the Collapse of the Shaker K+ Conductance by Specific Scorpion Toxins

2004 ◽  
Vol 123 (3) ◽  
pp. 265-279 ◽  
Author(s):  
Froylan Gómez-Lagunas ◽  
Cesar V.F. Batista ◽  
Timoteo Olamendi-Portugal ◽  
Martha E. Ramírez-Domínguez ◽  
Lourival D. Possani
Keyword(s):  
Binding Site ◽  
Selectivity Filter ◽  
Channel Block ◽  
Scorpion Toxins ◽  
K Channels ◽  
Outer Vestibule ◽  
Plausible Model ◽  
K Current ◽  
Do So ◽  
External K

The Shaker B K+ conductance (GK) collapses when the channels are closed (deactivated) in Na+ solutions that lack K+ ions. Also, it is known that external TEA (TEAo) impedes the collapse of GK (Gómez-Lagunas, F. 1997. J. Physiol. 499:3–15; Gómez-Lagunas, F. 2001. J. Gen. Physiol. 118:639–648), and that channel block by TEAo and scorpion toxins are two mutually exclusive events (Goldstein, S.A.N., and C. Miller. 1993. Biophys. J. 65:1613–1619). Therefore, we tested the ability of scorpion toxins to inhibit the collapse of GK in 0 K+. We have found that these toxins are not uniform regarding the capacity to protect GK. Those toxins, whose binding to the channels is destabilized by external K+, are also effective inhibitors of the collapse of GK. In addition to K+, other externally added cations also destabilize toxin block, with an effectiveness that does not match the selectivity sequence of K+ channels. The inhibition of the drop of GK follows a saturation relationship with [toxin], which is fitted well by the Michaelis-Menten equation, with an apparent Kd bigger than that of block of the K+ current. However, another plausible model is also presented and compared with the Michaelis-Menten model. The observations suggest that those toxins that protect GK in 0 K+ do so by interacting either with the most external K+ binding site of the selectivity filter (suggesting that the K+ occupancy of only that site of the pore may be enough to preserve GK) or with sites capable of binding K+ located in the outer vestibule of the pore, above the selectivity filter.

Potential-dependent block of human delayed rectifier K+ channels by internal Na+

1996 ◽  
Vol 270 (4) ◽  
pp. C1131-C1144 ◽  
Author(s):  
S. Johansson ◽  
A. K. Sundgren ◽  
U. Kahl
Keyword(s):  
Single Channel ◽  
Neuroblastoma Cells ◽  
Negative Slope ◽  
Delayed Rectifier ◽  
Na Current ◽  
Intact Cells ◽  
K Channels ◽  
High Potentials ◽  
K Current ◽  
K Currents

The delayed rectifier K+ currents in differentiated human SH-SY5Y neuroblastoma cells were characterized with tight-seal recording techniques. Activation and inactivation parameters were measured. At high positive potentials, the current showed a marked rectification, causing a region of negative slope conductance in the current vs. potential curve. The rectification depended markedly on the pipette Na+ concentration. Without Na+, no rectification was observed, whereas with high Na+ (20-60 mM), a marked rectification was always observed. Tail current measurements showed a fast ( < 400 microseconds) block of K+ currents in the presence of internal Na+. With 60 mM Na+ in the pipette 8% of the K+ current was blocked at 0 mV, 27% at +20 mV, and 82% at +100 mV. Similar degrees of block were often seen with 30 mM Na+ in the pipette. The submembrane Na+ concentration in intact cells was estimated, on the basis of the reversal of Na+ current, to be approximately 15 mM. Single-channel K+ currents, in the cell-attached configuration, showed a conductance of approximately 20 pS at 40-60 mV above rest but showed rectification at high potentials.

scholarly journals Adenosine Triphosphate Activates a Noninactivating K+ Current in Adrenal Cortical Cells through Nonhydrolytic Binding

1997 ◽  
Vol 110 (6) ◽  
pp. 679-692 ◽  
Author(s):  
John J. Enyeart ◽  
Juan Carlos Gomora ◽  
Lin Xu ◽  
Judith A. Enyeart
Keyword(s):  
Membrane Potential ◽  
Resting Potential ◽  
K Channel ◽  
Atp Binding ◽  
Cortisol Secretion ◽  
Open Probability ◽  
Metabolic State ◽  
K Channels ◽  
Wide Range ◽  
K Current

Bovine adrenal zona fasciculata (AZF) cells express a noninactivating K+ current (IAC) that is inhibited by adrenocorticotropic hormone and angiotensin II at subnanomolar concentrations. Since IAC appears to set the membrane potential of AZF cells, these channels may function critically in coupling peptide receptors to membrane depolarization, Ca2+ entry, and cortisol secretion. IAC channel activity may be tightly linked to the metabolic state of the cell. In whole cell patch clamp recordings, MgATP applied intracellularly through the patch electrode at concentrations above 1 mM dramatically enhanced the expression of IAC K+ current. The maximum IAC current density varied from a low of 8.45 ± 2.74 pA/pF (n = 17) to a high of 109.2 ± 26.3 pA/pF (n = 6) at pipette MgATP concentrations of 0.1 and 10 mM, respectively. In the presence of 5 mM MgATP, IAC K+ channels were tonically active over a wide range of membrane potentials, and voltage-dependent open probability increased by only ∼30% between −40 and +40 mV. ATP (5 mM) in the absence of Mg2+ and the nonhydrolyzable ATP analog AMP-PNP (5 mM) were also effective at enhancing the expression of IAC, from a control value of 3.7 ± 0.1 pA/pF (n = 3) to maximum values of 48.5 ± 9.8 pA/pF (n = 11) and 67.3 ± 23.2 pA/pF (n = 6), respectively. At the single channel level, the unitary IAC current amplitude did not vary with the ATP concentration or substitution with AMP-PNP. In addition to ATP and AMP-PNP, a number of other nucleotides including GTP, UTP, GDP, and UDP all increased the outwardly rectifying IAC current with an apparent order of effectiveness: MgATP &gt; ATP = AMP-PNP &gt; GTP = UTP &gt; ADP &gt;&gt; GDP &gt; AMP and ATP-γ-S. Although ATP, GTP, and UTP all enhanced IAC amplitude with similar effectiveness, inhibition of IAC by ACTH (200 pM) occurred only in the presence of ATP. As little as 50 μM MgATP restored complete inhibition of IAC, which had been activated by 5 mM UTP. Although the opening of IAC channels may require only ATP binding, its inhibition by ACTH appears to involve a mechanism other than hydrolysis of this nucleotide. These findings describe a novel form of K+ channel modulation by which IAC channels are activated through the nonhydrolytic binding of ATP. Because they are activated rather than inhibited by ATP binding, IAC K+ channels may represent a distinctive new variety of K+ channel. The combined features of IAC channels that allow it to sense and respond to changing ATP levels and to set the resting potential of AZF cells, suggest a mechanism where membrane potential, Ca2+ entry, and cortisol secretion could be tightly coupled to the metabolic state of the cell through the activity of IAC K+ channels.

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