Lysophosphatidic acid, serum, and hyposmolarity activate Cl- currents in corneal keratocytes

1995 ◽  
Vol 269 (6) ◽  
pp. C1385-C1393 ◽  
Author(s):  
M. A. Watsky
Keyword(s):  
Lysophosphatidic Acid ◽  
Reversal Potential ◽  
Flufenamic Acid ◽  
Disulfonic Acid ◽  
Hypotonic Stress ◽  
Outward Currents ◽  
Fetal Bovine ◽  
Patch Technique ◽  
Corneal Keratocytes ◽  
In Cells

The influence of serum, lysophosphatidic acid (LPA), and hyposmotic stress on the ion channel activity of normal and cryo-injured rabbit corneal keratocytes was investigated. Whole cell currents were examined using the amphotericin perforated-patch technique. In cells from wounded corneas, fetal bovine serum activated large, holding voltage-insensitive, fast-activating, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-, flufenamic acid-, and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB)-blockable outward currents showing inactivation at depolarized voltages. LPA activated identical currents, also only in cells from wounded corneas. Blocker and reversal potential experiments characterized the current as a Cl- currents (Icl). Lysophosphatidylcholine (10 microM) failed to activate the current. An identical current was activated by hyposmotic stimulation in cells from control and wounded corneas. Hyposmotic stimulation also activated Icl in cells from wounded corneas that were unresponsive to LPA. We conclude that serum, LPA, and hypotonic stress activate Icl in keratocytes from wounded corneas. We also conclude that LPA is a serum factor that can activate Icl and that hyposmotic activation may work through a signaling pathway separate from that of LPA.

scholarly journals Activation of Slo2.1 channels by niflumic acid

2010 ◽  
Vol 135 (3) ◽  
pp. 275-295 ◽  
Author(s):  
Li Dai ◽  
Vivek Garg ◽  
Michael C. Sanguinetti
Keyword(s):  
Voltage Dependence ◽  
Reversal Potential ◽  
Niflumic Acid ◽  
Flufenamic Acid ◽  
Channel Activation ◽  
Outward Currents ◽  
Transmembrane Voltage ◽  
High K ◽  
Charged Residues ◽  
K Current

Slo2.1 channels conduct an outwardly rectifying K+ current when activated by high [Na+]i. Here, we show that gating of these channels can also be activated by fenamates such as niflumic acid (NFA), even in the absence of intracellular Na+. In Xenopus oocytes injected with <10 ng cRNA, heterologously expressed human Slo2.1 current was negligible, but rapidly activated by extracellular application of NFA (EC50 = 2.1 mM) or flufenamic acid (EC50 = 1.4 mM). Slo2.1 channels activated by 1 mM NFA exhibited weak voltage dependence. In high [K+]e, the conductance–voltage (G-V) relationship had a V1/2 of +95 mV and an effective valence, z, of 0.48 e. Higher concentrations of NFA shifted V1/2 to more negative potentials (EC50 = 2.1 mM) and increased the minimum value of G/Gmax (EC50 = 2.4 mM); at 6 mM NFA, Slo2.1 channel activation was voltage independent. In contrast, V1/2 of the G-V relationship was shifted to more positive potentials when [K+]e was elevated from 1 to 300 mM (EC50 = 21.2 mM). The slope conductance measured at the reversal potential exhibited the same [K+]e dependency (EC50 = 23.5 mM). Conductance was also [Na+]e dependent. Outward currents were reduced when Na+ was replaced with choline or mannitol, but unaffected by substitution with Rb+ or Li+. Neutralization of charged residues in the S1–S4 domains did not appreciably alter the voltage dependence of Slo2.1 activation. Thus, the weak voltage dependence of Slo2.1 channel activation is independent of charged residues in the S1–S4 segments. In contrast, mutation of R190 located in the adjacent S4–S5 linker to a neutral (Ala or Gln) or acidic (Glu) residue induced constitutive channel activity that was reduced by high [K+]e. Collectively, these findings indicate that Slo2.1 channel gating is modulated by [K+]e and [Na+]e, and that NFA uncouples channel activation from its modulation by transmembrane voltage and intracellular Na+.

scholarly journals Expression of follistatin mRNA by somatotropes and mammotropes early in the rat estrous cycle.

1993 ◽  
Vol 41 (7) ◽  
pp. 955-960 ◽  
Author(s):  
B L Lee ◽  
G Unabia ◽  
G Childs
Keyword(s):  
Fetal Bovine Serum ◽  
S100 Protein ◽  
Thyroid Stimulating Hormone ◽  
Pituitary Cells ◽  
Folliculostellate Cells ◽  
Complementary Oligonucleotide ◽  
Fetal Bovine ◽  
In Cells ◽  
Stimulating Hormone

We previously found follistatin (FS) mRNA in gonadotropes [predominantly in cells with luteinizing hormone (LH) antigens] and folliculostellate cells (with S100 antigens) in diestrus rats pituitaries. However, earlier in the cycle, when percentages of gonadotropes are lowest, percentages of cells expressing FS are 1.5-2-fold higher than in diestrus. This study was designed to detect FS mRNA and other pituitary antigens to identify the additional cells with dual in situ hybridization and immunolabeling protocols. The mRNA was detected with biotinylated complementary oligonucleotide probes and avidin-biotin-peroxidase complexes. Significant labeling for FS mRNA was found in cells with the following antigens: growth hormone (GH) (7% of pituitary cells); prolactin (PRL) (5%); S100 protein (5%); follicle-stimulating hormone (FSH beta) (4%); LH beta (3%); and thyroid-stimulating hormone (TSH beta) (3%). Optimal conditions for detection included: overnight plating of > 50,000 cells/well (24-well tray) in media containing 10% fetal bovine serum; hybridization at 37 degrees C; and fixation in 2% glutaraldehyde. Whereas FS is expressed predominantly by LH gonadotropes at midcycle, FS mRNA can be expressed by all types of antigen-bearing cells earlier in the cycle. Its function in the pituitary may relate to its role in binding activin, which would result in inhibition of FSH release. However, since activin inhibits secretion of GH, PRL, and adrenocorticotropin (ACTH), FS may also control activin's effects on these cells. The FS-expressing cells may therefore be paracrine or autocrine regulators.

The contribution of a Ca(2+)-activated Cl(−) conductance to amino-acid-induced inward current responses of ciliated olfactory neurons of the rainbow trout

2000 ◽  
Vol 203 (2) ◽  
pp. 253-262 ◽  
Author(s):  
K. Sato ◽  
N. Suzuki
Keyword(s):  
Rainbow Trout ◽  
Amino Acid ◽  
Reversal Potential ◽  
Amino Acid Mixture ◽  
Niflumic Acid ◽  
Flufenamic Acid ◽  
Acid Mixture ◽  
Inward Currents ◽  
Cl Channels ◽  
Cl Conductance

To determine whether amino-acid-induced inward currents of ciliated olfactory receptor neurons (ORNs) in rainbow trout (Oncorhynchus mykiss) include a Ca(2+)-activated Cl(−) conductance, we first studied changes in reversal potential and the current/voltage relationships of the responses of ORNs to an amino acid mixture (l-alanine, l-arginine, l-glutamate and l-norvaline; all 10 mmol l(−)(1)) with different concentrations of Na(+) and Cl(−) in the perfusion and recording pipette solutions. We also examined the effects of six different Cl(−) channel blockers on the responses of ORNs using a conventional whole-cell voltage-clamp technique. The amino acid mixture and one blocker were applied focally to the cilia of ORNs using a double-barrelled micropipette and a pressure ejection system. The expected shifts in reversal potential, indicating the contribution of the Ca(2+)-activated Cl(−) conductance, occurred in both positive and negative directions depending on the external and internal Na(+) and Cl(−) concentrations. Niflumic acid, flufenamic acid, NPPB [5-nitro-2-(3-phenylpropylamino)-benzonate] and DCDPC (3′, 5-dichlorodiphenylamine-2-carboxylate), at 0.5 mmol l(−)(1), reversibly blocked both the amino-acid-induced inward currents and the background activity in most ORNs. The effectiveness of these blocking agents varied from 77 to 91 % for ORNs perfused externally with standard Ringer's solution. SITS (4-acetamido-4′-isothiocyanatostilbene-2,2′-disulphonate), at 5.0 mmol l(−)(1), irreversibly inhibited the physiological response (100 % inhibition), whereas DIDS (4,4′-diisothiocyanatostilbene-2, 2′-disulphonate), at 5.0 mmol l(−)(1), had the smallest effect (45 %) of the inhibitors tested. The dose of niflumic acid inducing 50 % inhibition (IC(50)), determined specifically for the current component of the Ca(2+)-activated Cl(−) channels, was 70 μmol l(−)(1). Our results suggest that these blockers are not specific for Ca(2+)-activated Cl(−) channels and that the density of these channels varies between individual ORNs. Our results also show that the Ca(2+)-activated Cl(−) conductance plays an important role in olfactory transduction and allows fishes to adapt to various ionic environments.

scholarly journals Small-conductance Ca2+-dependent K+ channels activated by ATP in murine colonic smooth muscle

1997 ◽  
Vol 273 (6) ◽  
pp. C2010-C2021 ◽  
Author(s):  
S. D. Koh ◽  
G. M. Dick ◽  
K. M. Sanders
Keyword(s):  
Smooth Muscle ◽  
Pyridoxal Phosphate ◽  
Single Channel ◽  
Outward Current ◽  
Disulfonic Acid ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Outward Currents ◽  
Murine Colon ◽  
Small Conductance

The patch-clamp technique was used to determine the ionic conductances activated by ATP in murine colonic smooth muscle cells. Extracellular ATP, UTP, and 2-methylthioadenosine 5′-triphosphate (2-MeS-ATP) increased outward currents in cells with amphotericin B-perforated patches. ATP (0.5–1 mM) did not affect whole cell currents of cells dialyzed with solutions containing ethylene glycol-bis(β-aminoethyl ether)- N, N, N′, N′-tetraacetic acid. Apamin (3 × 10−7M) reduced the outward current activated by ATP by 32 ± 5%. Single channel recordings from cell-attached patches showed that ATP, UTP, and 2-MeS-ATP increased the open probability of small-conductance, Ca2+-dependent K+ channels with a slope conductance of 5.3 ± 0.02 pS. Caffeine (500 μM) enhanced the open probability of the small-conductance K+ channels, and ATP had no effect after caffeine. Pyridoxal phosphate 6-azophenyl-2′,4′-disulfonic acid tetrasodium (PPADS, 10−4 M), a nonselective P2 receptor antagonist, prevented the increase in open probability caused by ATP and 2-MeS-ATP. PPADS had no effect on the response to caffeine. ATP-induced hyperpolarization in the murine colon may be mediated by P2y-induced release of Ca2+ from intracellular stores and activation of the 5.3-pS Ca2+-activated K+ channels.

Expression of the ornithine decarboxylase gene in response to asparagine in intestinal epithelial cells

1996 ◽  
Vol 271 (1) ◽  
pp. G164-G171 ◽  
Author(s):  
J. Y. Wang ◽  
M. J. Viar ◽  
P. M. Blanner ◽  
L. R. Johnson
Keyword(s):  
Ornithine Decarboxylase ◽  
Half Life ◽  
Cellular Protein ◽  
Mrna Levels ◽  
Intestinal Epithelial ◽  
Normal Rat ◽  
Fetal Bovine ◽  
Mucosal Growth ◽  
Rate Limiting ◽  
In Cells

Refeeding fasted rats significantly stimulates mucosal growth and ornithine decarboxylase (ODC), the rate-limiting enzyme in the biosynthesis of polyamines, but the exact mechanism responsible for induction of ODC at the molecular level is unknown. Of normal dietary constituents, the amino acid asparagine markedly increases ODC activity and mucosal growth when administered intragastrically. The current study examined the expression of the ODC gene in IEC-6 cells (a line of normal rat small intestinal crypt cells) after exposure to asparagine. Cells were grown in Dulbecco's minimal essential medium containing 5% dialyzed fetal bovine serum. They were deprived of serum for 24 h before experiments. Exposure to asparagine at the dose of 10 mM resulted in the rapid increase in ODC mRNA levels. The increased expression of the ODC gene began 1 h after and peaked between 3 and 5 h after treatment with asparagine. Maximum increases in ODC mRNA levels were approximately fivefold the normal value. Increased levels of ODC mRNA in cells exposed to asparagine were paralleled by increases in ODC protein and enzyme activity and cellular polyamine levels. The half-life of mRNA for ODC in unstimulated IEC-6 cells was approximately 30 min and increased to > 2 h in cells exposed to 10 mM asparagine. The half-life of ODC activity also was increased in asparagine-treated cells. When cellular protein synthesis was inhibited by cycloheximide, asparagine superinduced ODC mRNA levels. Furthermore, asparagine also significantly stimulated DNA synthesis in IEC-6 cells. These results indicate that 1) asparagine stimulates ODC in IEC-6 cells through multiple pathways and 2) increased ODC mRNA levels result partly from a delay in the rate of degradation. These findings suggest that luminal amino acids stimulate gut mucosal growth in association with their ability to regulate ODC gene expression.

Differences in outward currents between neonatal and adult rabbit ventricular cells

1994 ◽  
Vol 266 (3) ◽  
pp. H1184-H1194 ◽  
Author(s):  
J. Sanchez-Chapula ◽  
A. Elizalde ◽  
R. Navarro-Polanco ◽  
H. Barajas
Keyword(s):  
Action Potential ◽  
Papillary Muscle ◽  
Action Potential Duration ◽  
Outward Current ◽  
Stimulation Frequency ◽  
Transient Outward Current ◽  
Adult Rabbit ◽  
Outward Currents ◽  
Recovery From Inactivation ◽  
In Cells

In adult rabbit ventricular preparations, action potential duration is significantly increased when stimulation frequency is increased from 0.1 to 1.0 Hz. In neonatal preparations, a similar change in stimulation frequency produced no significant increase in action potential duration. To identify the ionic basis for this difference, we studied different outward currents in single myocytes from papillary muscle and from epicardial tissue of adult and neonatal rabbits. The densities of the outward currents in neonatal cells were about one-half of the current density in adult cells. The density of the voltage-activated transient outward current (I(to1)) was smaller in cells from papillary muscle than in cells from epicardium in adult and newborn rabbits. We found major differences in the kinetic behavior of I(to1) between adult and neonatal cells: 1) the rate of apparent inactivation was faster in neonatal cells, and 2) the recovery from inactivation was significantly faster in neonatal cells, with a time constant of 113 vs. 1,356 ms. We propose that this marked difference in the recovery from inactivation of I(to1) is the basis for the difference in frequency dependence of action potential duration.

Functional identification of a sarcolemmal chloride channel from bovine tracheal smooth muscle

1996 ◽  
Vol 271 (5) ◽  
pp. C1716-C1724 ◽  
Author(s):  
D. Salvail ◽  
A. Alioua ◽  
E. Rousseau
Keyword(s):  
Smooth Muscle ◽  
Lipid Bilayers ◽  
Reversal Potential ◽  
Tracheal Smooth Muscle ◽  
Disulfonic Acid ◽  
Equilibrium Potential ◽  
Functional Identification ◽  
Cl Channels ◽  
Cl Conductance

The biophysical and pharmacological characteristics of unitary Cl- currents from bovine tracheal smooth muscle cells were studied after reconstitution of microsomal vesicles into planar lipid bilayers. Two types of currents were recorded simultaneously in KCl buffer: the well-defined Ca(2+)-dependent K+ conductance [GK(Ca)] and a much smaller Cl- current, indicating that the Cl- channels under scrutiny originate from the same membrane as the GK(Ca)-type channels, the plasma membrane of airway smooth muscle (ASM) cells. The GK(Ca) activities were eliminated by the use of CsCl buffer. The average unitary Cl- conductance measured in 50 mM trans-250 mM cis CsCl was 77 +/- 6 pS (n = 21), and the reversal potential measured in various CsCl gradients followed the Cl- equilibrium potential as determined from the Nernst equation. In contrast with the previous reports describing the Ca2+ sensitivity of macroscopic ASM Cl- currents, this channel was found to be insensitive to cytoplasmic and extracellular Ca2+ levels. Phosphorylation cocktails, including protein kinases A, G, or C, did not alter the activity of the channel nor did changes in pH. Among a series of Cl- channel inhibitors, 4,4'-diisothiocyanostilbene-2, 2'-disulfonic acid [50% effective concentration (EC50) = 30 microM] and 5-nitro-2-(3-phenylpropylamino) benzoic acid (EC50 = 130 microM) were the most potent blockers of the current examined. The exact role of this surface Cl- conductance remains unclear, and its involvement in cellular activity needs further investigation.

Dendritic arbor of locus coeruleus neurons contributes to opioid inhibition

1996 ◽  
Vol 75 (5) ◽  
pp. 2029-2035 ◽  
Author(s):  
R. A. Travagli ◽  
M. Wessendorf ◽  
J. T. Williams
Keyword(s):  
Locus Coeruleus ◽  
Horizontal Plane ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Properties ◽  
Equilibrium Potential ◽  
Intrinsic Membrane Properties ◽  
In Cells

1. The nucleus locus coeruleus (LC) is made up of noradrenergic cells all of which are hyperpolarized by opioids. Recent work has shown that the reversal potential of the opioid-induced current is more negative than the potassium equilibrium potential. The aim of the present study was to determine whether the extent of the dendritic field could contribute to the very negative opioid reversal potential. 2. Individual LC cells were labeled in the brain slice preparation. The number of dendrites found on cells in slices sectioned in the horizontal plane was greater than cells in coronal slices. However, the dimensions of the cell body slices from each plane were not significantly different. 3. The resting conductance of neurons from slices cut in the horizontal plane was significantly larger than in cells from coronal plane. 4. The amplitude of the outward current induced by [Met5]-enkephalin (ME) was larger in cells from horizontal slices and the reversal potential was more negative than that of cells in coronal slices. 5. The results show that the plane of section influences the membrane properties and opioid actions of LC neurons in vitro and suggest that these differences correlate with the numbers of dendrites. The results suggest that in vivo, in addition to intrinsic membrane properties and synaptic inputs, the structural makeup of the nucleus is an important factor in determining the activity.

Intracellular calcium activates a chloride current in canine ventricular myocytes

1994 ◽  
Vol 267 (5) ◽  
pp. H1984-H1995 ◽  
Author(s):  
A. C. Zygmunt
Keyword(s):  
Potassium Current ◽  
Ventricular Myocytes ◽  
Single Cells ◽  
Reversal Potential ◽  
Outward Current ◽  
Chloride Current ◽  
Disulfonic Acid ◽  
Transient Outward Current ◽  
Triggered Arrhythmias ◽  
Inward Currents

The contribution of chloride and potassium to the 4-aminopyridine (4-AP)-resistant transient outward current was investigated in dog cardiac myocytes. Whole cell currents were recorded at 37 degrees C in single cells dissociated from epicardial and midmyocardial regions of the canine ventricle. Sodium-calcium exchange current and voltage-dependent transient outward potassium current (IA) were blocked in sodium-free solutions containing 2 mM 4-AP; sodium channels were inactivated by the -50-mV holding potential. When patch pipettes contained 0.4–0.8 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, voltage-clamp steps over the range -20 to +50 mV activated an inward calcium current (ICa) and a Ca(2+)-activated chloride current [ICl(Ca)]. ICl(Ca) was blocked by 200 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), or reduction of external chloride. Independent of the presence of potassium, the reversal potential of the SITS-sensitive current varied with extracellular chloride, as predicted for a chloride-selective conductance. The bell-shaped current-voltage relation of ICl(Ca) has a threshold of -20 mV and a peak at +40 mV. No evidence could be found for a Ca(2+)-activated potassium current or a Ca(2+)-activated nonspecific cation current under these conditions. ICl(Ca) contributed to oscillatory inward currents at diastolic potentials in cells superfused by isoproterenol and high Ca2+, suggesting a role for this current in triggered arrhythmias associated with delayed afterdepolarizations. In the normal heart, ICl(Ca) is likely to contribute to rate- and rhythm-dependent repolarization of the cardiac action potential.

Role of chloride currents in repolarizing rabbit atrial myocytes

1995 ◽  
Vol 268 (5) ◽  
pp. H1992-H2002 ◽  
Author(s):  
Z. Wang ◽  
B. Fermini ◽  
J. Feng ◽  
S. Nattel
Keyword(s):  
Action Potential ◽  
Reversal Potential ◽  
Outward Current ◽  
Cell Voltage ◽  
Disulfonic Acid ◽  
Transient Outward Current ◽  
Atrial Myocytes ◽  
Atrial Cells ◽  
K Current

Rabbit atrial cells manifest a prominent transient outward K+ current (Ito1), but this current recovers slowly from inactivation and is unlikely to be important at physiological rates (3-5 Hz). Depolarization of rabbit atrial cells also elicits a transient Ca(2+)-dependent outward Cl- current (Ito2). To compare the relative magnitude of these transient outward currents at various rates, we applied whole cell voltage-clamp techniques to isolated rabbit atrial myocytes. Whereas peak Ito1 exceeded Ito2 at slow rates (0.1 Hz), Ito1 was strongly reduced as rate was increased (by 97 +/- 2%, mean +/- SE, at 4 Hz), while Ito2 was slightly reduced (by 28 +/- 4%, 4 Hz). The reversal potential of transient outward tail currents at 0.07 Hz was -49 +/- 9 mV, while at 2.5 Hz the reversal potential became -18 +/- 7 mV (calculated Cl- reversal potential -18 mV). The addition of the Cl- transport blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 150 microM) or the replacement of external Cl- with methanesulfonate inhibited a large part of the transient outward current elicited by depolarization at 4 Hz. DIDS and Cl- replacement increased action potential duration in both single rabbit atrial cells and multicellular rabbit atrial preparations. We conclude that the Ca(2+)-dependent Cl- current is substantially larger than the transient K+ current at physiological rates in the rabbit and is likely to play a more important role in action potential repolarization than the latter current in this tissue in vivo.

Sign in / Sign up

Export Citation Format

Share Document