Spontaneous Ryanodine-Receptor-Dependent Ca2+-Activated K+ Currents and Hyperpolarizations in Rat Medial Preoptic Neurons

2010 ◽  
Vol 103 (5) ◽  
pp. 2900-2911 ◽  
Author(s):  
Göran Klement ◽  
Michael Druzin ◽  
David Haage ◽  
Evgenya Malinina ◽  
Peter Århem ◽  
...  
Keyword(s):  
Ryanodine Receptor ◽  
Ryanodine Receptors ◽  
Underlying Mechanism ◽  
Sk Channels ◽  
Patch Clamp Technique ◽  
Channel Activation ◽  
Impulse Generation ◽  
Outward Currents ◽  
Main Charge ◽  
Perforated Patch Clamp

The aim of the present study was to clarify the identity of slow spontaneous currents, the underlying mechanism and possible role for impulse generation in neurons of the rat medial preoptic nucleus (MPN). Acutely dissociated neurons were studied with the perforated patch-clamp technique. Spontaneous outward currents, at a frequency of ∼0.5 Hz and with a decay time constant of ∼200 ms, were frequently detected in neurons when voltage-clamped between approximately −70 and −30 mV. The dependence on extracellular K+ concentration was consistent with K+ as the main charge carrier. We concluded that the main characteristics were similar to those of spontaneous miniature outward currents (SMOCs), previously reported mainly for muscle fibers and peripheral nerve. From the dependence on voltage and from a pharmacological analysis, we concluded that the currents were carried through small-conductance Ca2+-activated (SK) channels, of the SK3 subtype. From experiments with ryanodine, xestospongin C, and caffeine, we concluded that the spontaneous currents were triggered by Ca2+ release from intracellular stores via ryanodine receptor channels. An apparent voltage dependence was explained by masking of the spontaneous currents as a consequence of steady SK-channel activation at membrane potentials > −30 mV. Under current-clamp conditions, corresponding transient hyperpolarizations occasionally exceeded 10 mV in amplitude and reduced the frequency of spontaneous impulses. In conclusion, MPN neurons display spontaneous hyperpolarizations triggered by Ca2+ release via ryanodine receptors and SK3-channel activation. Thus such events may affect impulse firing of MPN neurons.

scholarly journals Arginine Vasopressin Potentiates the Stimulatory Action of CRH on Pituitary Corticotropes via a Protein Kinase C–Dependent Reduction of the Background TREK-1 Current

Endocrinology ◽  
2015 ◽  
Vol 156 (10) ◽  
pp. 3661-3672 ◽  
Author(s):  
Andy K. Lee ◽  
Frederick W. Tse ◽  
Amy Tse
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Arginine Vasopressin ◽  
Underlying Mechanism ◽  
Sk Channels ◽  
Acth Secretion ◽  
Patch Clamp Technique ◽  
Stimulatory Action ◽  
Kinase C ◽  
Perforated Patch Clamp

The hypothalamic hormone arginine vasopressin (AVP) potentiates the stimulatory action of CRH on ACTH secretion from pituitary corticotropes, but the underlying mechanism is elusive. Using the perforated patch-clamp technique to monitor membrane potentials in mouse corticotropes, we found that AVP triggered a transient hyperpolarization that was followed by a sustained depolarization. The hyperpolarization was caused by intracellular Ca2+ release that in turn activated the small conductance Ca2+-activated K+ (SK) channels. The depolarization was due to the suppression of background TWIK-related K+ (TREK)-1 channels. Direct activation of protein kinase C (PKC) reduced the TREK-1 current, whereas PKC inhibition attenuated the AVP-mediated reduction of the TREK-1 current, implicating the involvement of PKC. The addition of CRH (which stimulates the protein kinase A pathway) in the presence of AVP, or vice versa, resulted in further suppression of the TREK-1 current. In corticotropes with buffered cytosolic Ca2+ concentration ([Ca2+]i), AVP evoked a sustained depolarization, and the coapplication of AVP and CRH caused a larger depolarization than that evoked by AVP or CRH alone. In cells with minimal perturbation of [Ca2+]i and background TREK-1 channels, CRH evoked a sustained depolarization that was superimposed with action potentials, and the subsequent coapplication of AVP and CRH triggered a transient hyperpolarization that was followed by a larger depolarization. In summary, AVP and CRH have additive effects on the suppression of the TREK-1 current, resulting in a more robust depolarization in corticotropes. We suggest that this mechanism contributes to the potentiating action of AVP on CRH-evoked ACTH secretion.

scholarly journals Intracellular calcium events activated by ATP in murine colonic myocytes

2000 ◽  
Vol 279 (1) ◽  
pp. C126-C135 ◽  
Author(s):  
Orline Bayguinov ◽  
Brian Hagen ◽  
Adrian D. Bonev ◽  
Mark T. Nelson ◽  
Kenton M. Sanders
Keyword(s):  
Ryanodine Receptors ◽  
Smooth Muscles ◽  
Sk Channels ◽  
Inhibitory Neurotransmitter ◽  
Outward Currents ◽  
Ionic Conductances ◽  
Visceral Muscles ◽  
Murine Colon ◽  
Spontaneous Transient Outward Currents ◽  
Purinergic Stimulation

ATP is a candidate enteric inhibitory neurotransmitter in visceral smooth muscles. ATP hyperpolarizes visceral muscles via activation of small-conductance, Ca2+-activated K+ (SK) channels. Coupling between ATP stimulation and SK channels may be mediated by localized Ca2+ release. Isolated myocytes of the murine colon produced spontaneous, localized Ca2+ release events. These events corresponded to spontaneous transient outward currents (STOCs) consisting of charybdotoxin (ChTX)-sensitive and -insensitive events. ChTX-insensitive STOCs were inhibited by apamin. Localized Ca2+ transients were not blocked by ryanodine, but these events were reduced in magnitude and frequency by xestospongin C (Xe-C), a blocker of inositol 1,4,5-trisphosphate receptors. Thus we have termed the localized Ca2+ events in colonic myocytes “Ca2+ puffs.” The P2Y receptor agonist 2-methylthio-ATP (2-MeS-ATP) increased the intensity and frequency of Ca2+ puffs. 2-MeS-ATP also increased STOCs in association with the increase in Ca2+ puffs. Pyridoxal-phospate-6-azophenyl-2′,4′-disculfonic acid tetrasodium, a P2 receptor inhibitor, blocked responses to 2-MeS-ATP. Spontaneous Ca2+ transients and the effects of 2-MeS-ATP on Ca2+ puffs and STOCs were blocked by U-73122, an inhibitor of phospholipase C. Xe-C and ryanodine also blocked responses to 2-MeS-ATP, suggesting that, in addition to release from IP3receptor-operated stores, ryanodine receptors may be recruited during agonist stimulation to amplify release of Ca2+. These data suggest that localized Ca2+ release modulates Ca2+-dependent ionic conductances in the plasma membrane. Localized Ca2+ release may contribute to the electrical responses resulting from purinergic stimulation.

Gramicidin perforated patch-clamp technique reveals glycine-gated outward chloride current in dissociated nucleus solitarii neurons of the rat

1994 ◽  
Vol 72 (3) ◽  
pp. 1103-1108 ◽  
Author(s):  
J. S. Rhee ◽  
S. Ebihara ◽  
N. Akaike
Keyword(s):  
Patch Clamp ◽  
Hill Coefficient ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Perforated Patch ◽  
Clamp Technique ◽  
Outward Currents ◽  
Patch Technique ◽  
Perforated Patch Clamp

1. The inhibitory response of exogenously applied glycine was investigated in freshly dissociated rat nucleus tractus solitarii neurons under whole cell configuration using new perforated patch-clamp technique termed "gramicidin perforated patch technique," which maintains intact intracellular Cl- concentrations. 2. Using the gramicidin perforated patch technique, at a holding potential (VH) of -45 mV, glycine induced outward currents in a concentration-dependent manner with a EC50 of 4.0 x 10(-5) M and at a Hill coefficient of 1.5. In contrast, using the nystatin perforated patch technique, glycine induced inward currents at the same VH in a concentration-dependent manner with an EC50 of 4.9 x 10(-5) M and at a Hill coefficient of 1.2. 3. The glycine-induced outward currents were blocked by strychnine in a concentration dependent manner with an IC50 of 2.2 x 10(-8) M. The blockade was competitive. 4. The current-voltage relationship for the 10(-5) M glycine response showed a clear outward rectification. 5. Ten-fold change of extracellular Cl- with a large impermeable anion resulted in a 65 mV shift of the reversal potential of glycine-induced currents (EGly), indicating that the membrane behaves like a Cl- electrode in the presence of glycine. 6. The intracellular Cl- activity calculated from the EGly ranged from 7.3 to 18.2 mM, with a mean value of 13.3 mM. 7. The values of EGly in the individual neurons were significantly negative to the resting membrane potentials, suggesting the existence of active transport of Cl-.

scholarly journals Spontaneous Transient Outward Currents Arise from Microdomains Where BK Channels Are Exposed to a Mean Ca2+ Concentration on the Order of 10 μM during a Ca2+ Spark

2002 ◽  
Vol 120 (1) ◽  
pp. 15-27 ◽  
Author(s):  
Ronghua ZhuGe ◽  
Kevin E. Fogarty ◽  
Richard A. Tuft ◽  
John V. Walsh
Keyword(s):  
Voltage Dependence ◽  
Ryanodine Receptors ◽  
Bk Channels ◽  
Bk Channel ◽  
Channel Activation ◽  
Membrane Area ◽  
Outward Currents ◽  
Cell Recording ◽  
Excised Patches ◽  
Spontaneous Transient Outward Currents

Ca2+ sparks are small, localized cytosolic Ca2+ transients due to Ca2+ release from sarcoplasmic reticulum through ryanodine receptors. In smooth muscle, Ca2+ sparks activate large conductance Ca2+-activated K+ channels (BK channels) in the spark microdomain, thus generating spontaneous transient outward currents (STOCs). The purpose of the present study is to determine experimentally the level of Ca2+ to which the BK channels are exposed during a spark. Using tight seal, whole-cell recording, we have analyzed the voltage-dependence of the STOC conductance (g(STOC)), and compared it to the voltage-dependence of BK channel activation in excised patches in the presence of different [Ca2+]s. The Ca2+ sparks did not change in amplitude over the range of potentials of interest. In contrast, the magnitude of g(STOC) remained roughly constant from 20 to −40 mV and then declined steeply at more negative potentials. From this and the voltage dependence of BK channel activation, we conclude that the BK channels underlying STOCs are exposed to a mean [Ca2+] on the order of 10 μM during a Ca2+ spark. The membrane area over which a concentration ≥10 μM is reached has an estimated radius of 150–300 nm, corresponding to an area which is a fraction of one square micron. Moreover, given the constraints imposed by the estimated channel density and the Ca2+ current during a spark, the BK channels do not appear to be uniformly distributed over the membrane but instead are found at higher density at the spark site.

Purinergic activation of spontaneous transient outward currents in guinea pig taenia colonic myocytes

2000 ◽  
Vol 278 (2) ◽  
pp. C352-C362 ◽  
Author(s):  
In Deok Kong ◽  
Sang Don Koh ◽  
Kenton M. Sanders
Keyword(s):  
Guinea Pig ◽  
Pyridoxal Phosphate ◽  
Receptor Blocker ◽  
Disulfonic Acid ◽  
Sk Channels ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
Relaxation Responses ◽  
Spontaneous Transient Outward Currents

Spontaneous transient outward currents (STOCs) were recorded from smooth muscle cells of the guinea pig taenia coli using the whole cell patch-clamp technique. STOCs were resolved at potentials positive to −50 mV. Treating cells with caffeine (1 mM) caused a burst of outward currents followed by inhibition of STOCs. Replacing extracellular Ca2+ with equimolar Mn2+ caused STOCs to “run down.” Iberiotoxin (200 nM) or charybdotoxin (ChTX; 200 nM) inhibited large-amplitude STOCs, but small-amplitude “mini-STOCs” remained in the presence of these drugs. Mini-STOCs were reduced by apamin (500 nM), an inhibitor of small-conductance Ca2+-activated K+ channels (SK channels). Application of ATP or 2-methylthioadenosine 5′-triphosphate (2-MeS-ATP) increased the frequency of STOCs. The effects of 2-MeS-ATP persisted in the presence of charybdotoxin but were blocked by combination of ChTX (200 nM) and apamin (500 nM). 2-MeS-ATP did not increase STOCs in the presence of pyridoxal phosphate 6-azophenyl-2′,4′-disulfonic acid, a P2 receptor blocker. Similarly, pretreatment of cells with U-73122 (1 μM), an inhibitor of phospholipase C (PLC), abolished the effects of 2-MeS-ATP. Xestospongin C, an inositol 1,4,5-trisphosphate (IP3) receptor blocker, attenuated STOCs, but these events were not affected by ryanodine. The data suggest that purinergic activation through P2Y receptors results in localized Ca2+ release via PLC- and IP3-dependent mechanisms. Release of Ca2+ is coupled to STOCs, which are composed of currents mediated by large-conductance Ca2+-activated K+ channels and SK channels. The latter are thought to mediate hyperpolarization and relaxation responses of gastrointestinal muscles to inhibitory purinergic stimulation.

Ca2+-activated ion currents triggered by ryanodine receptor-mediated Ca2+release control firing of inhibitory neurons in the prepositus hypoglossi nucleus

2013 ◽  
Vol 109 (2) ◽  
pp. 389-404 ◽  
Author(s):  
Yasuhiko Saito ◽  
Yuchio Yanagawa
Keyword(s):  
Ryanodine Receptors ◽  
Smooth Muscles ◽  
Firing Frequency ◽  
Neuronal Firing ◽  
Inhibitory Neurons ◽  
Sk Channels ◽  
Spontaneous Firing ◽  
Central Neurons ◽  
Outward Currents ◽  
Prepositus Hypoglossi

Spontaneous miniature outward currents (SMOCs) are known to exist in smooth muscles and peripheral neurons, and evidence for the presence of SMOCs in central neurons has been accumulating. SMOCs in central neurons are induced through Ca2+-activated K+(KCa) channels, which are activated through Ca2+-induced Ca2+release from the endoplasmic reticulum via ryanodine receptors (RyRs). Previously, we found that some neurons in the prepositus hypoglossi nucleus (PHN) showed spontaneous outward currents (SOCs). In the present study, we used whole cell recordings in slice preparations of the rat brain stem to investigate the following: 1) the ionic mechanisms of SOCs, 2) the types of neurons exhibiting frequent SOCs, and 3) the effect of Ca2+-activated conductance on neuronal firing. Pharmacological analyses revealed that SOCs were induced via the activation of small-conductance-type KCa(SK) channels and RyRs, indicating that SOCs correspond to SMOCs. An analysis of the voltage responses to current pulses of the fluorescence-expressing inhibitory neurons of transgenic rats revealed that inhibitory neurons frequently exhibited SOCs. Abolition of SOCs via blockade of SK channels enhanced the frequency of spontaneous firing of inhibitory PHN neurons. However, abolition of SOCs via blockade of RyRs reduced the firing frequency and hyperpolarized the membrane potential. Similar reductions in firing frequency and hyperpolarization were also observed when Ca2+-activated nonselective cation (CAN) channels were blocked. These results suggest that, in inhibitory neurons in the PHN, Ca2+release via RyRs activates SK and CAN channels, and these channels regulate spontaneous firing in a complementary manner.

H2O2 activates ryanodine receptor but has little effect on recovery of releasable Ca2+ content after fatigue

2002 ◽  
Vol 93 (6) ◽  
pp. 1999-2008 ◽  
Author(s):  
Toshiharu Oba ◽  
Chieko Kurono ◽  
Ritsuko Nakajima ◽  
Tetsuo Takaishi ◽  
Kazuto Ishida ◽  
...  
Keyword(s):  
Redox Potential ◽  
Lipid Bilayers ◽  
Ryanodine Receptor ◽  
Ryanodine Receptors ◽  
Control Level ◽  
Recovery Process ◽  
Channel Activity ◽  
Channel Activation ◽  
Stimulation Of

We studied whether hydrogen peroxide (H2O2) at ≤10 μM activates the ryanodine receptor and decreases releasable Ca2+ content in the sarcoplasmic reticulum after fatigue. Exposure of rabbit or frog skeletal muscle ryanodine receptors to 10 μM H2O2 enhanced channel activity in lipid bilayers when the redox potential was defined at cis = −220 mV and trans = −180 mV. Channel activation by 10 μM H2O2 was also observed when cispotential was set at −220 mV without defining transpotential, but the effect was less. Reduction of trans redox potential from −180 to −220 mV did not alter channel activity. H2O2 at 500 μM failed to activate the channel when the redox potential was not controlled. Stimulation of the frog muscle fiber for 2 min (50 Hz, a duty cycle of 200 ms/s) decreased tetanus tension by ∼50%. After 1 min, tetanus recovered rapidly to ∼70% of control and thereafter slowly approached the control level. Amplitudes of caffeine- and 4-chloro- m-cresol-induced contractures were decreased after a 60-min rest. The decrease is not enhanced by exposure to 10 μM H2O2. These results suggest that H2O2 markedly activates the ryanodine receptor under the redox control in vitro, but externally applied H2O2 may not play an important role in the postfatigue recovery process.

Glycine response in acutely dissociated ventromedial hypothalamic neuron of the rat: new approach with gramicidin perforated patch-clamp technique

1994 ◽  
Vol 72 (4) ◽  
pp. 1530-1537 ◽  
Author(s):  
Y. Abe ◽  
K. Furukawa ◽  
Y. Itoyama ◽  
N. Akaike
Keyword(s):  
Hill Coefficient ◽  
Induced Response ◽  
Monovalent Cations ◽  
Patch Clamp Technique ◽  
Perforated Patch ◽  
Outward Currents ◽  
Inhibition Concentration ◽  
Inward Currents ◽  
Perforated Patch Clamp ◽  
The Hill

1. We investigated the glycine-induced response in ventromedial hypothalamic (VMH) neurons freshly dissociated from 8- to 12-day-old rats using the nystatin and gramicidin perforated patch recording modes. The nystatin-formed pores in the plasma membrane are permeable for both monovalent cations and anions, whereas those formed by gramicidin are permeable only to monovalent cations. Therefore, when the patch-pipette contains 150 mM Cl- and gramicidin, the physiological intracellular Cl- concentration ([Cl-]i) is undisturbed in the cell-attached condition of the pipette. 2. At holding potentials of -40 to -60 mV, glycine induced inward currents and outward currents in the nystatin and gramicidin perforated patch recording modes, respectively. The values of the half-maximum effective concentration (EC50) and the Hill coefficient in the concentration-response relationships of the glycine responses were 2.9 x 10(-5) M, 1.1, and 4.2 x 10(-5) M, 1.4, respectively. These values were quite similar in both recording modes. 3. The reversal potentials of the glycine responses (EGly) were -1.5 mV in the nystatin perforated patch recording and -75.0 to -24.8 mV in the gramicidin perforated patch recording. 4. Strychnine (3 x 10(-8) M) inhibited the glycine-induced outward currents in a competitive manner and the half-inhibition concentration (IC50) of strychnine on the 10(-4) M glycine-induced response was 1.9 x 10(-8) M. 5. The physiological [Cl-]i in the VMH neurons calculated from the EGly obtained by the gramicidin perforated patch mode ranged from 6.0 to 43.8 mM (n = 28).

Nitric oxide mediates outward potassium currents in opossum esophageal circular smooth muscle

1996 ◽  
Vol 270 (6) ◽  
pp. G932-G938 ◽  
Author(s):  
J. Jury ◽  
K. R. Boev ◽  
E. E. Daniel
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Circular Muscle ◽  
Outward Current ◽  
Equilibrium Potential ◽  
Patch Clamp Technique ◽  
Pipette Solution ◽  
Whole Cell ◽  
Circular Smooth Muscle ◽  
Outward Currents

Single smooth muscle cells from the opossum body circular muscle were isolated and whole cell currents were characterized by the whole cell patch-clamp technique. When the cells were held at -50 mV and depolarized to 70 mV in 20-mV increments, initial small inactivating inward currents were evoked (-30 to 30 mV) followed by larger sustained outward currents. Depolarization from a holding potential of -90 mV evoked an initial fast inactivating outward current sensitive to 4-aminopyridine but not to high levels of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). The outward currents reversed near K+ equilibrium potential and were abolished when KCl was replaced by CsCl in the pipette solution. The sustained outward current was inhibited by quinine and cesium. High EGTA in the pipette solution reduced but did not abolish the sustained outward currents, suggesting that both Ca(2+)-dependent and -independent currents were evoked. The nitric oxide (NO)-releasing agents Sin-1 and sodium nitroprusside increased outward K+ currents. High levels of EGTA in the pipette solution abolished the increase in outward current induced by Sin-1. The presence of cyclopiazonic acid, an inhibitor of the sarcoplasmic reticulum (SR) Ca2+ pump, blocked the effects of NO-releasing agents. We conclude that NO release activates K+ outward currents in opossum esophagus circular muscle, which may depend on Ca2+ release from the SR stores.

scholarly journals Coupling of SK channels, L-type Ca2+ channels, and ryanodine receptors in cardiomyocytes

2018 ◽  
Vol 8 (1) ◽  
Author(s):  
Xiao-Dong Zhang ◽  
Zana A. Coulibaly ◽  
Wei Chun Chen ◽  
Hannah A. Ledford ◽  
Jeong Han Lee ◽  
...  
Keyword(s):  
Ryanodine Receptors ◽  
Sk Channels ◽  
Ca2 Channels
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