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)

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.

Acetylcholine potentiates acetylcholine-induced increases in K+ current in cat atrial myocytes

1995 ◽  
Vol 268 (3) ◽  
pp. H1313-H1321 ◽  
Author(s):  
Y. G. Wang ◽  
S. L. Lipsius
Keyword(s):  
Reversal Potential ◽  
Membrane Conductance ◽  
K Channel ◽  
Channel Blockers ◽  
Atrial Myocytes ◽  
Initial Exposure ◽  
Recovery Interval ◽  
Cell Recording ◽  
K Current ◽  
K Currents

A nystatin-perforated patch whole cell recording method was used to study the effects of acetylcholine (ACh) on ACh-induced K+ currents in atrial myocytes isolated from cat hearts. The general protocol involved an initial 4-min exposure to ACh (ACh1), followed by a 4-min washout in ACh-free Tyrode solution and then a second 4-min ACh exposure (ACh2). Voltage ramps (40 mV/s) between -130 and +30 mV were used to assess changes in total membrane conductance. ACh2 (10 microM) induced an increase in K+ conductance that was significantly larger than that induced by ACh1 (10 microM) at voltages both negative and positive to the reversal potential. The potentiated current induced by ACh2 reversed at about -80 mV and inwardly rectified at voltages positive to the reversal potential. External Ba2+ (5 mM) or tetraethylammonium (10 mM) abolished all ACh2-induced increases in membrane conductance. The sensitivity to K+ channel blockers, reversal potential, and the rectifying properties indicate that the current potentiated by ACh2 is a K+ current. Atropine (1 microM) blocked all effects of ACh on K+ currents. Potentiation of K+ current by ACh2 required 1) ACh1 concentrations > or = 1 microM, 2) ACh1 duration > or = 2 min, and 3) recovery interval > or = 2 min. We conclude that an initial exposure to ACh potentiates subsequent ACh-induced increases in K+ current. ACh-induced potentiation depends on the concentration and duration of the initial ACh exposure and the recovery interval between consecutive ACh exposures.(ABSTRACT TRUNCATED AT 250 WORDS)

Localized IP3-Evoked Ca2+ Release Activates a K+ Current in Primary Vagal Sensory Neurons

2004 ◽  
Vol 91 (5) ◽  
pp. 2344-2352 ◽  
Author(s):  
Robert E. Hoesch ◽  
Daniel Weinreich ◽  
Joseph P. Y. Kao
Keyword(s):  
Sensory Neurons ◽  
Reversal Potential ◽  
Nodose Ganglion ◽  
Ion Concentration ◽  
Equilibrium Potential ◽  
Nodose Ganglion Neurons ◽  
Patch Pipette ◽  
Intracellular Ca ◽  
K Current ◽  
Ganglion Neurons

Electrophysiological and microfluorimetric techniques were used to determine whether intracellular photorelease of caged IP3, and the consequent release of Ca2+, could trigger a Ca2+-activated K+ current ( IIP3). Photorelease of caged IP3 evoked an IIP3 that averaged 2.36 ± 0.35 (SE) pA/pF in 24 of 28 rabbit primary vagal sensory neurons (nodose ganglion neurons, NGNs) voltage-clamped at –50 mV. IIP3 was abolished by intracellular BAPTA (2 mM), a Ca2+ chelator. Changing the K+ equilibrium potential by increasing extracellular K+ ion concentration caused a predicted Nernstian shift in the reversal potential of IIP3. These results indicated that IIP3 was a Ca2+-dependent K+ current. IIP3 was unaffected by three common antagonists of Ca2+-activated K+ currents: bath-applied iberiotoxin (50 nM) or apamin (100 nM), and intracellular 8-Br-cAMP (100 μM) included in the patch pipette. We have previously demonstrated that both IP3-evoked Ca2+ release and Ca2+-induced Ca2+ release (CICR) are co-expressed in NGNs and that CICR can trigger a Ca2+-activated K+ current. In the present study, using caffeine, a CICR agonist, to selectively attenuate intracellular Ca2+ stores, we showed that IP3-evoked Ca2+ release occurs independently of CICR, but interestingly, that a component of IIP3 requires CICR. These data suggest that IP3-evoked Ca2+ release activates a K+ current that is pharmacologically distinct from other Ca2+-activated K+ currents in NGNs. We describe several models that explain our results based on Ca2+ signaling microdomains in NGNs.

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.

Serotonin activates a Ca(2+)-dependent K(+) current in identified peptidergic neurons from the crayfish

2000 ◽  
Vol 203 (4) ◽  
pp. 715-723 ◽  
Author(s):  
R. Alvarado-Alvarez ◽  
H. Arechiga ◽  
U. Garcia
Keyword(s):  
Procambarus Clarkii ◽  
Outward Current ◽  
Membrane Conductance ◽  
Neuronal Firing ◽  
Maximal Response ◽  
Red Pigment ◽  
K Current ◽  
Patch Configuration ◽  
K Concentration ◽  
Dose Dependent

The effects of 5-hydroxytryptamine (5-HT) were investigated in red pigment concentrating hormone (RPCH)-containing neurons isolated from the X-organ of the crayfish (Procambarus clarkii). Under current-clamp conditions and using the gramicidin-perforated-patch configuration, 5-HT elicited a prolonged hyperpolarization that suppressed neuronal firing concomitant with an increase in membrane conductance. Under voltage-clamp conditions, 5-HT evoked an outward current at a holding potential of −50 mV. This current reversed at an E(K) of −90 mV, which shifted by 30 mV when the extracellular K(+) concentration was increased from 5.4 to 19 mmol l(−1). The effect of 5-HT was dose-dependent within the range 1–100 micromol l(−1) and followed simple Michaelis-Menten kinetics, with a half-maximal response being elicited at 10 micromol l(−1). Preincubation with charybdotoxin (100 nmol l(−1)), tetraethylammonium (500 micromol l(−1)) or methysergide (100 micromol l(−1)) was effective in blocking the response to 5-HT. These results suggest that 5-HT is an inhibitory mediator of the release of red pigment concentrating hormone by acting on a Ca(2+)-dependent K(+) current.

scholarly journals Calcium-induced calcium release in noradrenergic neurons of the locus coeruleus

2019 ◽  
Author(s):  
Hiroyuki Kawano ◽  
Sara B. Mitchell ◽  
Jin-Young Koh ◽  
Kirsty M. Goodman ◽  
N. Charles Harata
Keyword(s):  
Locus Coeruleus ◽  
Calcium Release ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Conductance ◽  
Cytosolic Calcium ◽  
Equilibrium Potential ◽  
Calcium Stores ◽  
Patch Clamp Recording ◽  
Calcium Induced Calcium Release

ABSTRACTThe locus coeruleus (LC) is a nucleus within the brainstem that consists of norepinephrine-releasing neurons. It is involved in broad processes including autonomic regulation, and cognitive and emotional functions such as arousal, attention and anxiety. Understanding the mechanisms that control the excitability of LC neurons is important because they innervate widespread regions of the central nervous system. One of the key regulators is the cytosolic calcium concentration ([Ca2+]c), the increases in which can be amplified by calcium-induced calcium release (CICR) from the intracellular calcium stores. Although the electrical activities of LC neurons are regulated by changes in [Ca2+]c, the extent of CICR involvement in this regulation has remained unclear. Here we show that CICR hyperpolarizes acutely dissociated LC neurons of the rat brain and demonstrate the pathway whereby it does this. When CICR was activated by extracellular application of 10 mM caffeine, LC neurons were hyperpolarized in the current-clamp mode of the patch-clamp recording, and the majority of neurons showed an outward current in the voltage-clamp mode. This outward current was accompanied by an increase in membrane conductance, and its reversal potential was close to the K+ equilibrium potential, indicating that it is mediated by the opening of K+ channels. The outward current was generated in the absence of extracellular calcium and was blocked when the calcium stores were inhibited by applying ryanodine. Pharmacological experiments indicated that the outward current was mediated by Ca2+-activated K+ channels of the non-small conductance type. Finally, the application of caffeine led to an increase in the [Ca2+]c in these neurons, as visualized by fluorescence microscopy. These findings delineate a mechanism whereby CICR suppresses the electrical activity of LC neurons, and indicate that it could play a dynamic role in modulating the LC-mediated noradrenergic tone in the brain.

Heterogeneous Actions of Serotonin on Interneurons in Rat Visual Cortex

2003 ◽  
Vol 89 (3) ◽  
pp. 1278-1287 ◽  
Author(s):  
Zixiu Xiang ◽  
David A. Prince
Keyword(s):  
Receptor Antagonist ◽  
Receptor Agonist ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Conductance ◽  
Pyramidal Cells ◽  
Equilibrium Potential ◽  
Inward Current ◽  
Outward Currents ◽  
Layer V

The effects of serotonin (5-HT) on excitability of two cortical interneuronal subtypes, fast-spiking (FS) and low threshold spike (LTS) cells, and on spontaneous inhibitory postsynaptic currents (sIPSCs) in layer V pyramidal cells were studied in rat visual cortical slices using whole-cell recording techniques. Twenty-two of 28 FS and 26 of 35 LTS interneurons responded to local application of 5-HT. In the group of responsive neurons, 5-HT elicited an inward current in 50% of FS cells and 15% of LTS cells, an outward current was evoked in 41% of FS cells and 81% of LTS cells, and an inward current followed by an outward current in 9% of FS cells and 4% LTS cells. The inward and outward currents were blocked by a 5-HT3 receptor antagonist, tropisetron, and a 5-HT1A receptor antagonist, NAN-190, respectively. The 5-HT–induced inward and outward currents were both associated with an increase in membrane conductance. The estimated reversal potential was more positive than −40 mV for the inward current and close to the calculated K+equilibrium potential for the outward current. The 5-HT application caused an increase, a decrease, or an increase followed by a decrease in the frequency of sIPSCs in pyramidal cells. The 5-HT3 receptor agonist 1-( m-chlorophenyl) biguanide increased the frequency of larger and fast-rising sIPSCs, whereas the 5-HT1Areceptor agonist (±)8-hydroxydipropylaminotetralin hydrobromide elicited opposite effects and decreased the frequency of large events. These data indicate that serotonergic activation imposes complex actions on cortical inhibitory networks, which may lead to changes in cortical information processing.

Nitric Oxide Activates Leak K+ Currents in the Presumed Cholinergic Neuron of Basal Forebrain

2007 ◽  
Vol 98 (6) ◽  
pp. 3397-3410 ◽  
Author(s):  
Youngnam Kang ◽  
Yoshie Dempo ◽  
Atsuko Ohashi ◽  
Mitsuru Saito ◽  
Hiroki Toyoda ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Basal Forebrain ◽  
Reversal Potential ◽  
Soluble Guanylyl Cyclase ◽  
Outward Current ◽  
Pump Current ◽  
Atp Depletion ◽  
Equilibrium Potential ◽  
No Donor ◽  
Bath Application

Learning and memory are critically dependent on basal forebrain cholinergic (BFC) neuron excitability, which is modulated profoundly by leak K+ channels. Many neuromodulators closing leak K+ channels have been reported, whereas their endogenous opener remained unknown. We here demonstrate that nitric oxide (NO) can be the endogenous opener of leak K+ channels in the presumed BFC neurons. Bath application of 1 mM S-nitroso- N-acetylpenicillamine (SNAP), an NO donor, induced a long-lasting hyperpolarization, which was often interrupted by a transient depolarization. Soluble guanylyl cyclase inhibitors prevented SNAP from inducing hyperpolarization but allowed SNAP to cause depolarization, whereas bath application of 0.2 mM 8-bromoguanosine-3′,5′-cyclomonophosphate (8-Br-cGMP) induced a similar long-lasting hyperpolarization alone. These observations indicate that the SNAP-induced hyperpolarization and depolarization are mediated by the cGMP-dependent and -independent processes, respectively. When examined with the ramp command pulse applied at –70 mV under the voltage-clamp condition, 8-Br-cGMP application induced the outward current that reversed at K+ equilibrium potential ( EK) and displayed Goldman-Hodgkin-Katz rectification, indicating the involvement of voltage-independent K+ current. By contrast, SNAP application in the presumed BFC neurons either dialyzed with the GTP-free internal solution or in the presence of 10 μM Rp-8-bromo-β-phenyl-1,N2-ethenoguanosine 3′,5′-cyclic monophosphorothioate sodium salt, a protein kinase G (PKG) inhibitor, induced the inward current that reversed at potentials much more negative than EK and close to the reversal potential of Na+-K+ pump current. These observations strongly suggest that NO activates leak K+ channels through cGMP-PKG-dependent pathway to markedly decrease the excitability in BFC neurons, while NO simultaneously causes depolarization by the inhibition of Na+-K+ pump through ATP depletion.

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.

Neuronal Sodium Leak Channel Is Responsible for the Detection of Sodium in the Rat Median Preoptic Nucleus

2011 ◽  
Vol 105 (2) ◽  
pp. 650-660 ◽  
Author(s):  
Christina Tremblay ◽  
Emmanuelle Berret ◽  
Mélaine Henry ◽  
Benjamin Nehmé ◽  
Louis Nadeau ◽  
...  
Keyword(s):  
Close Contact ◽  
Critical Role ◽  
Reversal Potential ◽  
Outward Current ◽  
The Body ◽  
Equilibrium Potential ◽  
Preoptic Nucleus ◽  
Leak Channel ◽  
Median Preoptic Nucleus ◽  
Electrophysiological Recordings

Sodium (Na+) ions are of primary importance for hydromineral and cardiovascular homeostasis, and the level of Na+ in the body fluid compartments [plasma and cerebrospinal fluid (CSF)] is precisely monitored in the hypothalamus. Glial cells seem to play a critical role in the mechanism of Na+ detection. However, the precise role of neurons in the detection of extracellular Na+ concentration ([Na+]out) remains unclear. Here we demonstrate that neurons of the median preoptic nucleus (MnPO), a structure in close contact with the CSF, are specific Na+ sensors. Electrophysiological recordings were performed on dissociated rat MnPO neurons under isotonic [Na+] (100 mM NaCl) with local application of hypernatriuric (150, 180 mM NaCl) or hyponatriuric (50 mM NaCl) external solution. The hyper- and hyponatriuric conditions triggered an in- and an outward current, respectively. The reversal potential of the current matched the equilibrium potential of Na+, indicating that a change in [Na+]out modified the influx of Na+ in the MnPO neurons. The conductance of the Na+ current was not affected by either the membrane potential or the [Na+]out. Moreover, the channel was highly selective for lithium over guanidinium. Together, these data identified the channel as a Na+ leak channel. A high correlation between the electrophysiological recordings and immunofluorescent labeling for the NaX channel in dissociated MnPO neurons strongly supports this channel as a candidate for the Na+ leak channel responsible for the Na+-sensing ability of rat MnPO neurons. The absence of NaX labeling and of a specific current evoked by a change in [Na+]out in mouse MnPO neurons suggests species specificity in the hypothalamus structures participating in central Na+ detection.

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