Arachidonic acid inhibits potassium conductances in cultured rat oligodendrocytes

1995 ◽  
Vol 269 (2) ◽  
pp. C341-C348 ◽  
Author(s):  
B. Soliven ◽  
N. Wang
Keyword(s):  
Arachidonic Acid ◽  
Second Messengers ◽  
Membrane Depolarization ◽  
Patch Clamp Technique ◽  
Metabolic Products ◽  
Potassium Conductances ◽  
K Current ◽  
Intracellular Second Messengers ◽  
Inwardly Rectifying ◽  
K Currents

Arachidonic acid (AA) and its metabolites play a dual role as intracellular second messengers and as transcellular mediators of neural activity. We have previously shown that AA increases cytosolic Ca2+ in oligodendrocytes. In this work, we studied the effects of AA and other fatty acids on whole cell K+ currents of cultured rat oligodendrocytes using the patch-clamp technique. We found that 1) AA decreased the current amplitudes of both the inwardly rectifying K+ current (IKir) and the outward K+ currents (IKo) resulting in membrane depolarization; 2) AA also induced IKo current inactivation/blocked state; 3) AA appeared to act directly on K+ channels and not indirectly via its metabolic products, activation of protein kinase C, or by generation of oxygen free radicals. We have thus demonstrated an additional mechanism for AA-induced signaling in oligodendrocytes, i.e., via modulation of K+ conductances leading to membrane depolarization. The latter has been shown to influence protein phosphorylation and perhaps other important functional output of oligodendrocytes.

PACAP38 Modulates Activity of NMDA Receptors in Cultured Chick Cortical Neurons

1997 ◽  
Vol 78 (4) ◽  
pp. 2231-2234 ◽  
Author(s):  
Guo Jun Liu ◽  
Barry W. Madsen
Keyword(s):  
Nmda Receptor ◽  
Nmda Receptors ◽  
Cortical Neurons ◽  
Second Messengers ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Low Concentrations ◽  
Channel Opening ◽  
Pituitary Adenylate Cyclase ◽  
Intracellular Second Messengers

Liu, Guo Jun and Barry W. Madsen. PACAP38 modulates activity of NMDA receptors in cultured chick cortical neurons. J. Neurophysiol. 78: 2231–2234, 1997. The outside-out recording mode of the patch-clamp technique was used to study modulatory effects of pituitary adenylate cyclase-activating polypeptide (PACAP38) on N-methyl-d-aspartate (NMDA) receptor activity in cultured chick cortical neurons. Biphasic concentration-dependent effects of PACAP38 on channel opening frequency induced by NMDA (20 μM) and glycine (1 μM) were found, with low concentrations (0.5–2 nM) of PACAP38 increasing activity and higher concentrations (10–1,000 nM) causing inhibition. These effects were reversible, reduced with higher concentrations of glycine (2–10 μM) but not by 200 μM NMDA, and inhibited by 10 μM 7-chlorokynurenic acid. In addition, 1 μM PACAP6–38 (a PACAP antagonist) inhibited channel activity due to 20 μM NMDA and 1 μM glycine by 66%, and this inhibition was reduced to 13% in the additional presence of 2 nM PACAP38. These observations suggest thatPACAP38 has a direct modulatory effect on the NMDA receptor that is independent of intracellular second messengers and probably mediated through the glycine coagonist site(s).

Isolated bovine retinal pigment epithelial cells express delayed rectifier type and M-type K+ currents

1997 ◽  
Vol 273 (3) ◽  
pp. C790-C803 ◽  
Author(s):  
M. Takahira ◽  
B. A. Hughes
Keyword(s):  
Retinal Pigment Epithelial ◽  
Retinal Pigment ◽  
Retinal Pigment Epithelial Cells ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Rpe Cells ◽  
Pigment Epithelial ◽  
Type K ◽  
K Current ◽  
K Currents

Outwardly rectifying K+ currents in freshly isolated bovine retinal pigment epithelial (RPE) cells were characterized using the whole cell and perforated-patch configurations of the patch-clamp technique. All cells exhibited a delayed rectifier type K+ current. This current had an activation threshold voltage of approximately -40 mV, activated with a sigmoidal trajectory, and inactivated completely over a period of several seconds. External tetraethylammonium (TEA) was an effective blocker of the delayed rectifier current [apparent dissociation constant (Kd) = 5.1 mM], but external Ba2+ was relatively ineffective. Approximately 24% of the cells also exhibited a sustained outwardly rectifying K+ current that became activated at voltages positive to approximately -80 mV. This current resembled the neuronal M-current. External Ba2+ was a potent blocker of this current (apparent Kd = 1.1 mM), but external TEA and Cs+ were relatively ineffective. These results indicate that freshly isolated bovine RPE cells express K+ currents of both the delayed rectifier and M types. The latter may contribute to the resting K+ conductances of the apical and basolateral membranes.

Blockade by lithium ions of potassium channels in rat anterior pituitary cells

1991 ◽  
Vol 261 (2) ◽  
pp. C218-C223 ◽  
Author(s):  
M. Kato ◽  
P. M. Lledo ◽  
J. D. Vincent
Keyword(s):  
Growth Hormone ◽  
Anterior Pituitary ◽  
Hormone Secretion ◽  
Male Rats ◽  
Delayed Rectifier ◽  
Pituitary Cells ◽  
Patch Clamp Technique ◽  
Anterior Pituitary Cells ◽  
K Current ◽  
K Currents

Extracellular Li+ has been known to facilitate the basal secretion of growth hormone from anterior pituitary cells and of catecholamine from chromaffin cells. In both cases, the intracellular accumulation of Li+ seems to be the prerequisite, and the presence of extracellular Ca2+ is indispensable. In this series of experiments, we examined whether Li+ blocked K+ currents by using primary cultured anterior pituitary cells from male rats. K+ currents were measured in the whole cell configuration of the patch-clamp technique. Extracellular Li+ (140 mM) suppressed both the delayed rectifier K+ current (IK) and the transient outward K+ current to 71 and 69% of control, respectively, in a reversible manner. IK elicited by a voltage step to +70 mV from holding potential of -70 mV was suppressed by 32.5 mM internal Li+ to 28% of control. Half-maximal suppression of K+ conductance by internal Li+ was 16 mM. Furthermore, Ca(2+)-channel blocker methoxyverapamil potently suppressed Li(+)-induced growth hormone secretion. From these results we propose that the blockade by Li+ of K+ channels could depolarize the cells and activate Ca2+ channels, thereby promoting the influx of Ca2+ and hormone secretion as a mechanism of Li(+)-induced hormone secretion.

Expression of CFTR controls cAMP-dependent activation of epithelial K+ currents

1996 ◽  
Vol 271 (5) ◽  
pp. C1565-C1573 ◽  
Author(s):  
G. Loussouarn ◽  
S. Demolombe ◽  
R. Mohammad-Panah ◽  
D. Escande ◽  
I. Baro
Keyword(s):  
Cftr Gene ◽  
High Concentration ◽  
Patch Clamp Technique ◽  
Whole Cell ◽  
Transfected Cells ◽  
Cyclic Monophosphate ◽  
K Current ◽  
Patch Configuration ◽  
Camp Stimulation ◽  
K Currents

The perforated-patch configuration of the patch-clamp technique was used to record whole cell currents from human epithelial CFPAC-1 cells defective for functional cystic fibrosis transmembrane conductance regulator (CFTR). In CFPAC-1 cells, adenosine 3',5'-cyclic monophosphate (cAMP) stimulation with forskolin (10 microM) plus 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (400 microM) activated neither Cl- nor K+ currents. In the same cells transfected with wild-type CFTR gene, cAMP stimulation produced activation of both Cl- and K+ currents. In Cl(-)-depleted medium (gluconate as a substitute), cAMP stimulation evoked a K+ current in CFTR-transfected but not in untransfected CFPAC-1 cells. This cAMP-evoked K+ current was the sum of two components: 1) a time-independent inwardly rectifying component, and 2) a slowly relaxing component activated at positive voltages. Increasing intracellular Ca2+ with ionomycin (1 microM) activated K+ currents in either transfected or untransfected cells. In transfected cells, blocking the CFTR conductance with high-concentration glibenclamide (100 microM) reduced the K+ current when activated by cAMP but not when activated by Ca2+. Pretreating CFTR-transfected cells for 48 h with interferon-gamma downregulated CFTR gene expression and reduced cAMP but not Ca2+ activation of the whole cell K+ current. From these results, we conclude that functional membrane CFTR protein influences activation by cAMP of epithelial K+ currents.

Whole cell membrane currents in cultured pig endocardial endothelial cells

1995 ◽  
Vol 268 (5) ◽  
pp. H2036-H2047 ◽  
Author(s):  
P. F. Fransen ◽  
M. J. Demolder ◽  
D. L. Brutsaert
Keyword(s):  
Endothelial Cells ◽  
Vascular Endothelium ◽  
Cell Swelling ◽  
Disulfonic Acid ◽  
Patch Clamp Technique ◽  
Pipette Solution ◽  
Whole Cell ◽  
K Current ◽  
Endocardial Endothelial Cells ◽  
Inwardly Rectifying

The whole cell mode of the patch-clamp technique was applied to cultured endocardial endothelial cells from the porcine right ventricle to study their electrophysiological properties. With isotonic pipette and bathing solutions (300-310 mosmol/kgH2O), single endocardial endothelial cells had resting membrane potentials ranging from -20 to -90 mV (mean = -55 +/- 20 mV, n = 48). In voltage-clamp experiments, the main membrane current was an inwardly rectifying K+ current with all characteristics described for the inwardly rectifying K+ current in vascular endothelium. Outward currents at positive clamp potentials were small, but when cell swelling was induced by means of a hypertonic pipette or hypotonic bathing solution and ATP (5 mM) was present in the pipette solution, a large outwardly rectifying current developed. This volume-activated current was insensitive to extracellular K+ or Na+ concentration variations but sensitive to changes in extracellular Cl- concentrations. It was inhibited in the presence of 4,4'-diisothiocyanostilbene-2,2 disulfonic acid (100-300 microM) and flufenamic acid (50-100 microM). Volume-activated Cl- channels are different from the stretch-activated cationic channels described in vascular endothelium and might be involved in the regulation of cell volume or the response to mechanical stretch.

scholarly journals Action of Certain Tropine Esters on Voltage-Clamped Lobster Axon

1968 ◽  
Vol 51 (3) ◽  
pp. 309-319 ◽  
Author(s):  
M. P. Blaustein
Keyword(s):  
Action Potential ◽  
Benzene Ring ◽  
Pulse Duration ◽  
Membrane Conductance ◽  
Giant Axon ◽  
Membrane Depolarization ◽  
K Current ◽  
Axonal Excitability ◽  
Voltage Axis ◽  
K Currents

Tropine p-tolylacetate (TPTA) and its quaternary analogue, tropine p-tolylacetate methiodide (TPTA MeI) decrease the early transient (Na) and late (K) currents in the voltage-clamped lobster giant axon. These agents, which block the nerve action potential, reduce the maximum Na and K conductance increases associated with membrane depolarization. They also slow the rate at which the sodium conductance is increased and shift the (normalized) membrane conductance vs. voltage curves in the direction of depolarization along the voltage axis. All these effects are qualitatively similar to those resulting from the action of procaine on the voltage-clamped axon. One unusual effect of the tropine esters, noticeable particularly at large depolarization steps, is that they cause the late, K current to reach a peak and then fall off with increasing pulse duration. This effect has not been reported to occur as a result of procaine action. Tropine p-chlorophenyl acetate (TPClϕA), which differs from TPTA only by the substitution of a p-Cl for a p-CH3 group on the benzene ring, had a negligible effect on axonal excitability.

Lamellipod extension and K+ current in osteoclasts are regulated by different types of G proteins

1994 ◽  
Vol 107 (2) ◽  
pp. 517-526 ◽  
Author(s):  
S.A. Arkett ◽  
S.J. Dixon ◽  
S.M. Sims
Keyword(s):  
Molecular Mass ◽  
G Protein ◽  
G Proteins ◽  
Actin Polymerization ◽  
Complete Suppression ◽  
Patch Clamp Technique ◽  
Membrane Area ◽  
Whole Cell ◽  
K Current ◽  
Inwardly Rectifying

Osteoclasts are the cells responsible for the resorption of bone and other mineralized tissues. GTP-binding proteins (G proteins) play important roles in regulating the activity of many cell types; however, there is limited knowledge of their functions in osteoclasts. We used the patch-clamp technique in the whole-cell configuration to introduce either hydrolysis-resistant guanosine triphosphate analogues or fluoroaluminate into single rat osteoclasts, and examined the effects of G protein activation on cell morphology and ionic conductances. Guanosine 5′-O-(3-thiotriphosphate) or 5′-guanylyl-imidodiphosphate, but not the control compounds adenosine 5′-O-(3-thiotriphosphate) or guanosine 5′-O-(2-thiodiphosphate), induced: (1) prompt spreading due to extension of lamellipodia; and (2) after a latency of several minutes, complete suppression of the inwardly rectifying K+ current. Pertussis toxin did not alter either spreading or suppression of K+ current induced by guanosine 5′-O-(3-thiotriphosphate). Cytochalasin D, but not colchicine, prevented guanosine 5′-O-(3-thiotriphosphate)-induced spreading, consistent with actin polymerization underlying lamellipod extension. Whole-cell capacitance did not change during guanosine 5′-O-(3-thiotriphosphate)-induced spreading, which is consistent with a lack of change in total plasma membrane area. Fluoroaluminate did not induce spreading, but it did suppress the K+ current. The differential effects of fluoroaluminate and guanosine 5′-O-(3-thiotriphosphate) suggest that lamellipod extension is regulated by a small molecular mass, monomeric G protein, whereas the inwardly rectifying K+ current is regulated by a large molecular mass, heterotrimeric G protein. Thus, osteoclast motility and ion transport are regulated by separate G protein-coupled pathways.

Development of inwardly rectifying K+ channel family in rat ventricular myocytes

1997 ◽  
Vol 272 (4) ◽  
pp. H1741-H1750 ◽  
Author(s):  
L. H. Xie ◽  
M. Takano ◽  
A. Noma
Keyword(s):  
Single Channel ◽  
Ventricular Myocytes ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
K Current ◽  
Inwardly Rectifying

The ATP-sensitive K+ current (I(K,ATP)), the inward rectifier K+ current (I(K1)), and the acetylcholine-activated K+ current (I(K,ACh)) were recorded in fetal, neonatal, and adult rat ventricular myocytes using the patch-clamp technique. The density (pA/pF) of I(K1) increased from gestation day 10 through neonatal day 1 and then decreased after neonatal day 30. The density of I(K,ATP) activated maximally by metabolic inhibition changed in parallel with the I(K1) density, and the density of I(K,ATP) channel distribution was 1.3 times higher than that of I(K1) throughout the development. We failed to observe developmental changes in the single-channel conductance and the mean open time of I(K1) and I(K,ATP) channels. However, the open probability of the I(K,ATP) channel was lower in fetuses, and the sensitivity to ATP was highest in 1-day neonates. I(K,ACh) were present in the ventricle at all stages of development but at a much lower density than in atrium. The relationship between the resting membrane potential and the development of the inwardly rectifying K-channel family is discussed.

G protein-mediated inhibition of inwardly rectifying K+ channels in guinea pig chromaffin cells

1993 ◽  
Vol 265 (4) ◽  
pp. C946-C956 ◽  
Author(s):  
M. Inoue ◽  
I. Imanaga
Keyword(s):  
Guinea Pig ◽  
G Protein ◽  
Chromaffin Cells ◽  
Negative Slope ◽  
Equilibrium Potential ◽  
Patch Clamp Technique ◽  
K Channels ◽  
K Current ◽  
Gamma S ◽  
Inwardly Rectifying

Properties of inwardly directed rectification and its G protein-mediated inhibition in guinea pig chromaffin cells were studied using the whole cell version of the patch-clamp technique. The current-voltage (I-V) relationship for plateau currents in response to a 50-ms pulse showed an inwardly directed rectification between -80 and -140 mV and a negative slope at more negative potentials in normal solution. Replacement of Na+ with N-methyl-D-glucamine (NMDG) in the perfusate did not alter the plateau I-V relationship between -110 and -130 mV but did abolish the negative slope below -140 mV. The zero current or resting membrane potential in the NMDG solution was in fair agreement with the equilibrium potential for K+. The chord conductance-voltage relationship showed a good fit with the Boltzmann equation and shifted along the voltage axis by an approximate change in driving force on K+ when K+ concentration was increased. External Cs+ and Ba2+ produced a voltage-dependent inhibition of the inwardly directed rectification. These results indicate that inwardly rectifying (IR) K+ channels are mediating an inwardly directed rectification. Intracellular dialysis with guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) produced a complete suppression of this IR K+ channel, irrespective of treatment with pertussis toxin. Adding GTP or guanosine 5'-O-(2-thiodiphosphate) to the patch solution resulted in a decrease in GTP gamma S inhibition of the K+ current. Internal application of vanadate was without effect. Time course of the inhibition of the IR K+ current coincided in part with that of inactivation of a nonselective cation current. In conclusion, IR K+ channels in the chromaffin cell are subject to G protein-mediated inhibition.

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.

Sign in / Sign up

Export Citation Format

Share Document