Calcium-activated, voltage-dependent, non-selective cation currents in endosperm plasma membrane from higher plants

1989 ◽  
Vol 237 (1287) ◽  
pp. 213-231 ◽  
Keyword(s):  
Plasma Membranes ◽  
Single Channel ◽  
Higher Plants ◽  
Outward Current ◽  
Monovalent Cation ◽  
Channel Blockers ◽  
Whole Cell ◽  
Whole Cell Patch Clamp ◽  
Single Burst ◽  
Subsequent Exposure

Single-channel and whole-cell patch-clamp techniques were used to characterize the electrophysiological behaviour of plasma membranes from freshly isolated, non-enzyme-treated endosperm protoplasts. A non-selective monovalent cation channel with a single-channel conductance of 22 pS in solutions with physiological potassium concentrations was observed in inside-out patches. The channel passes outward current at depolarized potentials and is highly selective for cations over anions, but discriminates poorly between lithium, sodium, potassium, rubidium and caesium ions. Specific potassium channel blockers were ineffective. The channel kinetics were apparently complex, with burst-like openings and rapid closures within a single burst. Single-channel openings were more frequent both for depolarizing pulses and maintained positive potentials. Channel activity was also increased by elevated cytoplasmic concentrations of either calcium or barium. Subsequent exposure of patches to low calcium, EGTA-buffered solutions resulted in large decreases in activity. Under whole-cell current clamp, small negative resting potentials were observed. A slowly developing outward current evoked by depolarizing pulses was seen in whole-cell recordings.

Ion channels in rabbit cultured fibroblasts

1986 ◽  
Vol 227 (1246) ◽  
pp. 1-16 ◽  
Keyword(s):  
Calcium Concentration ◽  
Voltage Dependence ◽  
Single Channel ◽  
Outward Current ◽  
Patch Clamp Technique ◽  
Cultured Fibroblasts ◽  
Whole Cell ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
High Conductance

Large outward currents are recorded with the whole-cell patch-clamp technique on depolarization of rabbit cultured fibroblasts. Our findings suggest that these outward currents consist of two voltage-dependent components, one of which also depends on cytoplasmic calcium concentration. Total replacement of external Cl - by the large anion ascorbate does not affect the amplitude of the currents, indicating that both components must be carried by K + . Consistent with these findings with whole-cell currents, in single channel recordings from fibroblasts we found that most patches contain high-conductance potassium-selective channels whose activation depends on both membrane potential and the calcium concentration at the cytoplasmic surface of the membrane. In a smaller number of patches, a second population of high-conductance calcium-independent potassium channels is observed having different voltage-dependence. The calcium- and voltage-dependence suggest that these two channels correspond with the two components of outward current seen in the whole-cell recordings. The single channel conductance of both channels in symmetrical KCl (150 mM) is 260-270 pS. Both channels are highly selective for K + over both Na + and Cl - . The conductance of the channels when outward current is carried by Rb + is considerably smaller than when it is carried by K + . Some evidence is adduced to support the hypothesis that these potassium channel populations may be involved in the control of cell proliferation.

Whole cell current analyses of pancreatic acinar AR42J cells. I. Voltage- and Ca(2+)-activated currents

1991 ◽  
Vol 260 (5) ◽  
pp. C934-C948 ◽  
Author(s):  
K. Kusano ◽  
H. Gainer
Keyword(s):  
Reversal Potential ◽  
Outward Current ◽  
Pancreatic Acinar Cells ◽  
Equilibrium Potential ◽  
Channel Blockers ◽  
Whole Cell ◽  
Inward Current ◽  
Tail Current ◽  
Ar42j Cells ◽  
Conductance Increase

Voltage- and Ca(2+)-activated whole cell currents were studied in AR42J cells, a clonal cell line derived from rat pancreatic acinar cells, using a patch electrode voltage-clamp technique. Four kinds of ionic currents were identified by their ionic dependencies, pharmacological properties, and kinetic parameters: 1) an outward current flow due mainly to a voltage-dependent K(+)-conductance increase, 2) an initial transient inward current due to an Na(+)-conductance increase, 3) transient and long-duration inward current due to a Ca(2+)-conductance increase, and 4) a slowly activating inward current that persists over the duration of the depolarizing pulse and deactivates slowly upon repolarization, producing a slow inward tail current. The slow inward tail current was particularly robust and was interpreted as due to a Ca(2+)-activated Cl(-)-conductance increase, since 1) the generation of this current was blocked by removing the extracellular Ca2+, applying Ca(2+)-channel blockers (Cd2+, nifedipine), or by lowering the intracellular Ca2+ concentration [( Ca2+]i) with EGTA; and 2) the reversal potential (Erev) of the slow inward tail current was close to 0 mV in the control condition (152 mM [Cl-]o/154 mM [Cl-]i), and changes of the [Cl-]o/[Cl )i ratio shifted the Erev toward the predicted Cl- equilibrium potential.

Electrophysiological properties of cultured outer medullary collecting duct cells

1992 ◽  
Vol 263 (6) ◽  
pp. F1004-F1010 ◽  
Author(s):  
C. A. Pappas ◽  
B. M. Koeppen
Keyword(s):  
Collecting Duct ◽  
Extracellular Fluid ◽  
Outward Current ◽  
Membrane Voltage ◽  
Disulfonic Acid ◽  
Channel Blockers ◽  
Dependent Manner ◽  
Whole Cell ◽  
Electrophysiological Properties ◽  
Medullary Collecting Duct

Whole cell patch-clamp techniques were used to characterize the electrophysiological properties of cells from the inner stripe portion of the rabbit outer medullary collecting duct (OMCDi) grown in primary culture. With pipette and bathing solutions mimicking intracellular and extracellular fluid, the resting membrane voltage was -30 to -40 mV. The whole cell conductance exhibited slight outward rectification, and at the resting membrane voltage the cell conductance averaged 2.58 +/- 0.49 nS (n = 17). The major conductive ion species was Cl-. The Cl- conductance was also found to have a significant permeability to HCO3- and was inhibited by the Cl(-)-channel blockers diphenylamine carboxylic acid and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. A small K+ conductance was also present, but no Na+ conductance was detected. Current generated by the H(+)-adenosinetriphosphatase (H(+)-ATPase) was quantitated. This current was dependent on the presence of ATP in the pipette. Dicyclohexylcarbodiimide, N-ethylmaleimide, and bafilomycin A1, inhibitors of the vacuolar H(+)-ATPase, also reduced this outward current in an ATP-dependent manner. The inhibitor-sensitive component of the outward current, a measure of the current generated by the H(+)-ATPase, was in the range of 35-100 pA/cell.

Transient potassium currents in avian sensory neurons

1990 ◽  
Vol 63 (4) ◽  
pp. 725-737 ◽  
Author(s):  
S. K. Florio ◽  
C. D. Westbrook ◽  
M. R. Vasko ◽  
R. J. Bauer ◽  
J. L. Kenyon
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Potassium Currents ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Small Component ◽  
Whole Cell ◽  
Outward Currents

1. We used the patch-clamp technique to study voltage-activated transient potassium currents in freshly dispersed and cultured chick dorsal root ganglion (DRG) cells. Whole-cell and cell-attached patch currents were recorded under conditions appropriate for recording potassium currents. 2. In whole-cell experiments, 100-ms depolarizations from normal resting potentials (-50 to -70 mV) elicited sustained outward currents that inactivated over a time scale of seconds. We attribute this behavior to a component of delayed rectifier current. After conditioning hyperpolarizations to potentials negative to -80 mV, depolarizations elicited transient outward current components that inactivated with time constants in the range of 8-26 ms. We attribute this behavior to a transient outward current component. 3. Conditioning hyperpolarizations increased the rate of activation of the net outward current implying that the removal of inactivation of the transient outward current allows it to contribute to early outward current during depolarizations from negative potentials. 4. Transient current was more prominent on the day the cells were dispersed and decreased with time in culture. 5. In cell-attached patches, single channels mediating outward currents were observed that were inactive at resting potentials but were active transiently during depolarizations to potentials positive to -30 mV. The probability of channels being open increased rapidly (peaking within approximately 6 ms) and then declined with a time constant in the range of 13-30 ms. With sodium as the main extracellular cation, single-channel conductances ranged from 18 to 32 pS. With potassium as the main extracellular cation, the single-channel conductance was approximately 43 pS, and the channel current reversed near 0 mV, as expected for a potassium current. 6. We conclude that the transient potassium channels mediate the component of transient outward current seen in the whole-cell experiments. This current is a relatively small component of the net current during depolarizations from normal resting potentials, but it can contribute significant outward current early in depolarizations from hyperpolarized potentials.

Characterization of a swelling-induced chloride conductance in cultured rat epididymal cells

1993 ◽  
Vol 265 (4) ◽  
pp. C997-C1005 ◽  
Author(s):  
H. C. Chan ◽  
W. O. Fu ◽  
Y. W. Chung ◽  
S. J. Huang ◽  
T. S. Zhou ◽  
...  
Keyword(s):  
Kinase Inhibitor ◽  
Disulfonic Acid ◽  
Channel Blockers ◽  
Induced Current ◽  
Whole Cell ◽  
Cyclic Monophosphate ◽  
Whole Cell Patch Clamp ◽  
Current Activation ◽  
Ethanesulfonic Acid ◽  
Cl Conductance

Swelling-induced Cl- conductance in cultured rat epididymal cells was characterized using whole cell patch-clamp techniques. Activation of whole cell current with an outwardly rectifying current-potential relationship was observed in cells exposed to hyposmotic solutions. This current was determined, from the observed current-reversal potentials at different Cl- concentrations, to be Cl- selective. The anion selectivity sequence of the swelling-induced Cl- conductance was I- approximately NO3- approximately Br- > Cl- > 2-(N-morpholino)ethanesulfonic acid. The swelling-induced Cl- conductance was reversibly inhibited by different Cl- channel blockers. Unlike diphenylamine-2-carboxylate or 5-nitro-2-(3-phenylpropylamino)-benzoate, which showed voltage-independent blockade, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid showed a marked voltage-dependent blockade of the volume-sensitive Cl- current, with a greater effect at depolarizing voltages. The swelling-induced Cl- conductance appeared to be different from the Ca(2+)- or adenosine 3',5'-cyclic monophosphate-activated Cl- conductances on the basis of the following observations: 1) swelling-induced current activation was seen even in the presence of kinase inhibitor (H-8) or absence of external free Ca2+, and 2) further increase in current activation could be produced by swelling after Ca(2+)- or adenosine 3',5'-cyclic monophosphate-induced current activation. The swelling-induced Cl- conductance may be involved in regulating epithelial cell volume as well as serving other important epididymal functions such as facilitating transepithelial secretion of organic compounds.

Opening of large-conductance calcium-activated potassium channels by the substituted benzimidazolone NS004

1994 ◽  
Vol 71 (5) ◽  
pp. 1873-1882 ◽  
Author(s):  
M. C. McKay ◽  
S. I. Dworetzky ◽  
N. A. Meanwell ◽  
S. P. Olesen ◽  
P. H. Reinhart ◽  
...  
Keyword(s):  
Rat Brain ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Outward Current ◽  
Calcium Sensitivity ◽  
Bk Channels ◽  
Gh3 Cells ◽  
Xenopus Laevis Oocytes ◽  
Planar Lipid Bilayers ◽  
Whole Cell

1. We used electrophysiological techniques to examine the effects of 5-trifluoromethyl-1-(5-chloro-2-hydroxyphenyl)-1,3-dihydro-2H-benzimidaz ole- 2-one (NS004) on large-conductance calcium-activated potassium (BK) channels. 2. We used recordings from excised membrane patches (cell-attached and inside-out single-channel configurations) and whole-cell patch-clamp recordings to examine the effects of NS004 on single BK channels and whole-cell outward currents, respectively, in rat GH3 clonal pituitary tumor cells. We also tested NS004 on voltage-clamped BK channels isolated from rat brain plasma membrane preparations and reconstituted into planar lipid bilayers. Finally, we used two-electrode voltage-clamp techniques to study the effects of NS004 on currents expressed in Xenopus laevis oocytes by the recently described Slo BK clone from Drosophila. 3. In GH3 cells and in Xenopus oocytes expressing the Slo gene product NS004 produced an increase in an iberiotoxin- or tetraethylammonium-sensitive whole-cell outward current, respectively. NS004 produced a significant increase in the activity of single GH3 cell BK channels and rat brain BK channels reconstituted into planar lipid bilayers. In both systems this was characterized by an increase in channel mean open time, a decrease in interburst interval, and an apparent increase in channel voltage/calcium sensitivity. 4. These data indicate that NS004 could be useful for investigating the biophysical and molecular properties of BK channels and for determining the functional consequences of the opening of BK channels.

Basolateral K+ conductance in principal cells of rat CCD

2005 ◽  
Vol 288 (3) ◽  
pp. F493-F504 ◽  
Author(s):  
Daniel A. Gray ◽  
Gustavo Frindt ◽  
Yu-Yang Zhang ◽  
Lawrence G. Palmer
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Whole Cell ◽  
Principal Cells ◽  
Luminal Membrane ◽  
High K ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Cell Current ◽  
Single Channel Currents

Whole cell K+ current was measured by forming seals on the luminal membrane of principal cells in split-open rat cortical collecting ducts. The mean inward, Ba2+-sensitive conductance, with 40 mM extracellular K+, was 76 ± 12 and 141 ± 22 nS/cell for animals on control and high-K+ diets, respectively. The apical contribution to this was estimated to be 3 and 16 nS/cell on control and high-K+ diets, respectively. To isolate the basolateral component of whole cell current, we blocked ROMK channels with either tertiapin-Q or intracellular acidification to pH 6.6. The current was weakly inward rectifying when bath K+ was ≥40 mM but became more strongly rectified when bath K+ was lowered into the physiological range. Including 1 mM spermine in the pipette moderately increased rectification, but most of the outward current remained. The K+ current did not require intracellular Ca2+ and was not inhibited by 3 mM ATP in the pipette. The negative log of the acidic dissociation constant (p Ka) was ∼6.5. Block by extracellular Ba2+ was voltage dependent with apparent Ki at −40 and −80 mV of ∼160 and ∼80 μM, respectively. The conductance was TEA insensitive. Substitution of Rb+ or NH4+ for K+ led to permeability ratios of 0.65 ± 0.07 and 0.15 ± 0.02 and inward conductance ratios of 0.17 ± 0.03 and 0.57 ± 0.09, respectively. Analysis of Ba2+-induced noise, with 40 mM extracellular K+, yielded single-channel currents of 0.39 ± 0.04 and −0.28 ± 0.04 pA at voltages of 0 and −40 mV, respectively, and a single-channel conductance of 17 ± 1 pS.

Persistent Na+ conductance in medium-sized neostriatal neurons: characterization using infrared videomicroscopy and whole cell patch-clamp recordings

1995 ◽  
Vol 74 (3) ◽  
pp. 1343-1348 ◽  
Author(s):  
C. Cepeda ◽  
S. H. Chandler ◽  
L. W. Shumate ◽  
M. S. Levine
Keyword(s):  
Patch Clamp ◽  
Sodium Current ◽  
Repetitive Firing ◽  
Channel Blockers ◽  
Potential Generation ◽  
Whole Cell ◽  
Cell Patch Clamp ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
Ramp Voltage

1. In the present study we investigate the expression of a persistent Na+ conductance (INaP) in identified medium-sized neostriatal neurons. Nomarski optics and infrared videomicroscopy were used for cell visualization and identification in thick slices (350 microns). Current- and voltage-clamp recordings were obtained utilizing whole cell patch-clamp methodology. 2. Application of depolarizing ramp voltage commands from a holding potential of -70 mV induced a slow, noninactivating inward current that occurred before and independent of the rapidly inactivating sodium current that subserves action potential generation. INaP began to activate at potentials less negative than -70 mV and peaked at -34 +/- 1 (SE) mV. Its average peak amplitude was -100 +/- 17 pA. INaP was abolished by tetrodotoxin (TTX, 0.5-1 microM) or an Na(+)-free solution. In contrast, it was not affected by Ca2+ channel blockers. Depolarizing ramp commands also induced tetraethylammonium-sensitive outward currents. 3. Dopamine (DA) (20-100 microM) produced a significant reduction of INaP. 4. These results demonstrate the existence of a TTX-sensitive persistent Na+ conductance in medium-sized neostriatal neurons. This conductance is modulated by DA and could play a role in the generation of rhythmic oscillations and in supporting repetitive firing.

Sign in / Sign up

Export Citation Format

Share Document