scholarly journals A novel action of quinine and quinidine on the membrane conductance of neurons from the vertebrate retina.

1994 ◽  
Vol 104 (6) ◽  
pp. 1039-1055 ◽  
Author(s):  
R P Malchow ◽  
H Qian ◽  
H Ripps
Keyword(s):  
Lucifer Yellow ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Conductance ◽  
Cobalt Acetate ◽  
Cinchona Alkaloids ◽  
Horizontal Cells ◽  
Patch Clamp Technique ◽  
Voltage Dependent ◽  
Gap Junctional

The cinchona alkaloids quinine and quinidine have been shown to block a broad range of voltage-gated membrane conductances in a variety of excitable tissues. Using the whole-cell version of the patch clamp technique, we examined the effects of these compounds on voltage-dependent currents from horizontal cells dissociated enzymatically from the all-rod retina of the skate. We report here a novel and unexpected action of quinine and quinidine on isolated horizontal cells. In addition to blocking several of the voltage-activated currents of these cells, the introduction of the alkaloids evoked a large outward current when the cells were held at depolarized potentials. Using tail current analysis, the reversal potential of the outward current was close to O mV, and the current was markedly suppressed by extracellularly applied cobalt, acetate, and halothane. Depolarization in the presence of quinine also permitted entry into the cells of extracellularly applied Lucifer yellow (MW = 443 D), whereas a 3-kD fluorescein-dextran complex was excluded. These findings suggest that the large, apparently nonselective conductance induced by quinine and quinidine results from the opening of hemi-gap junctional channels.

A transient voltage-dependent outward current in cultured cerebellar granules

1989 ◽  
Vol 9 (4) ◽  
pp. 451-457 ◽  
Author(s):  
Mauro Robello ◽  
Corrado Carignani ◽  
Carla Marchetti
Keyword(s):  
Granule Cells ◽  
Low Voltage ◽  
Reversal Potential ◽  
Outward Current ◽  
Mean Value ◽  
Transient Current ◽  
Patch Clamp Technique ◽  
Current Decay ◽  
Voltage Dependent ◽  
Pure Cell

Granule cells were dissociated from rat cerebella with a procedure that yields a 98% pure cell population. Potassium currents in these cells were studied using the patch-clamp technique. Depolarizing pulses of 10 mV step and 100 ms duration from a holding potential of −80 mV elicited two different potassium outward currents: a transient, low-voltage activated component and a long lasting, high-voltage activated component. At +30 mV, the total current reached an amplitude of 2 nA (mean value of 15 experiments). The reversal potential of the transient current, estimated by measuring tail currents, was −77 mV, close to that predicted by the Nernst equation. The transient current was half inactivated with a holding potential of −78 mV and completely inactivated with −50 mV or more positive holding potentials. Finally, the current decay could be fitted by the sum of two exponentials with time constants of about 20 and 250 ms.

scholarly journals A whole-cell and single-channel study of the voltage-dependent outward potassium current in avian hepatocytes.

1988 ◽  
Vol 91 (2) ◽  
pp. 255-274 ◽  
Author(s):  
C Marchetti ◽  
R T Premont ◽  
A M Brown
Keyword(s):  
Single Channel ◽  
Reversal Potential ◽  
Outward Current ◽  
Single Type ◽  
K Channel ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Voltage Dependent ◽  
Single Channel Currents ◽  
K Currents

Voltage-dependent membrane currents were studied in dissociated hepatocytes from chick, using the patch-clamp technique. All cells had voltage-dependent outward K+ currents; in 10% of the cells, a fast, transient, tetrodotoxin-sensitive Na+ current was identified. None of the cells had voltage-dependent inward Ca2+ currents. The K+ current activated at a membrane potential of about -10 mV, had a sigmoidal time course, and did not inactivate in 500 ms. The maximum outward conductance was 6.6 +/- 2.4 nS in 18 cells. The reversal potential, estimated from tail current measurements, shifted by 50 mV per 10-fold increase in the external K+ concentration. The current traces were fitted by n2 kinetics with voltage-dependent time constants. Omitting Ca2+ from the external bath or buffering the internal Ca2+ with EGTA did not alter the outward current, which shows that Ca2+-activated K+ currents were not present. 1-5 mM 4-aminopyridine, 0.5-2 mM BaCl2, and 0.1-1 mM CdCl2 reversibly inhibited the current. The block caused by Ba was voltage dependent. Single-channel currents were recorded in cell-attached and outside-out patches. The mean unitary conductance was 7 pS, and the channels displayed bursting kinetics. Thus, avian hepatocytes have a single type of K+ channel belonging to the delayed rectifier class of K+ channels.

BICUCULLINE/BACLOFEN-INSENSITIVE GABA RESPONSE IN CRUSTACEAN NEURONES IN CULTURE

1994 ◽  
Vol 191 (1) ◽  
pp. 167-193
Author(s):  
C Jackel ◽  
W Krenz ◽  
F Nagy
Keyword(s):  
Reversal Potential ◽  
Membrane Conductance ◽  
Gamma Aminobutyric Acid ◽  
Action Potential Firing ◽  
Patch Clamp Technique ◽  
Conformationally Restricted ◽  
Whole Cell Patch Clamp ◽  
Gabac Receptor ◽  
Potential Firing ◽  
Sr 95531

Neurones were dissociated from thoracic ganglia of embryonic and adult lobsters and kept in primary culture. When gamma-aminobutyric acid (GABA) was applied by pressure ejection, depolarizing or hyperpolarizing responses were produced, depending on the membrane potential. They were accompanied by an increase in membrane conductance. When they were present, action potential firing was inhibited. The pharmacological profile and ionic mechanism of GABA-evoked current were investigated under voltage-clamp with the whole-cell patch-clamp technique. The reversal potential of GABA-evoked current depended on the intracellular and extracellular Cl- concentration but not on extracellular Na+ and K+. Blockade of Ca2+ channels by Mn2+ was also without effect. The GABA-evoked current was mimicked by application of the GABAA agonists muscimol and isoguvacine with an order of potency muscimol>GABA>isoguvacine. cis-4-aminocrotonic acid (CACA), a folded and conformationally restricted GABA analogue, supposed to be diagnostic for the vertebrate GABAC receptor, also induced a bicuculline-resistant chloride current, although with a potency about 10 times lower than that of GABA. The GABA-evoked current was largely blocked by picrotoxin, but was insensitive to the GABAA antagonists bicuculline, bicuculline methiodide and SR 95531 at concentrations of up to 100 µmol l-1. Diazepam and phenobarbital did not exert modulatory effects. The GABAB antagonist phaclophen did not affect the GABA-induced current, while the GABAB agonists baclophen and 3-aminopropylphosphonic acid (3-APA) never evoked any response. Our results suggest that lobster thoracic neurones in culture express a chloride-conducting GABA-receptor channel which conforms to neither the GABAA nor the GABAB types of vertebrates but shows a pharmacology close to that of the novel GABAC receptor described in the vertebrate retina.

Voltage-dependent calcium channel current in isolated gallbladder smooth muscle cells of guinea pig

1993 ◽  
Vol 264 (6) ◽  
pp. G1066-G1076 ◽  
Author(s):  
T. Shimada
Keyword(s):  
Smooth Muscle ◽  
Guinea Pig ◽  
Smooth Muscle Cells ◽  
Time Course ◽  
Reversal Potential ◽  
High Sensitivity ◽  
Muscle Cells ◽  
Patch Clamp Technique ◽  
Decay Component ◽  
Voltage Dependent

The voltage-dependent Ca2+ current was studied in enzymatically dispersed guinea pig gallbladder smooth muscle cells using the whole cell patch-clamp technique. Depolarizing voltage (V) steps induced an inward current (I) that was carried by Ca2+. The threshold potential was -40 to -30 mV, the maximal current was observed at +10 to +20 mV, and the reversal potential was around +80 mV. I-V curves obtained with holding potentials of -80 and -40 mV were not significantly different. This current had a high sensitivity to dihydropyridine drugs, and the Ba2+ or Sr2+ current was larger than the Ca2+ current. Activation was accelerated by increasing the membrane potential. In general, the time course of decay was well fitted by the sum of two exponentials, but consideration of a third (ultra-slow) decay component was also necessary when the current generated by a 2-s command pulse was analyzed. Superimposition of activation and inactivation curves showed the presence of a significant window current. Carbachol suppressed the Ca2+ current only when the pipette contained a low concentration of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. These results show that the L-type Ca2+ current is dominant in gallbladder smooth muscle cells and may contribute to excitation-contraction coupling.

Ca2+-activated Cl− current can be triggered by Na+ current-induced SR Ca2+ release in rabbit ventricle

1999 ◽  
Vol 277 (4) ◽  
pp. H1467-H1477 ◽  
Author(s):  
Hui Sun ◽  
Denis Chartier ◽  
Stanley Nattel ◽  
Normand Leblanc
Keyword(s):  
Ventricular Myocytes ◽  
Physiological Role ◽  
Reversal Potential ◽  
Outward Current ◽  
External Solution ◽  
Rabbit Heart ◽  
Transient Outward Current ◽  
Release Mechanism ◽  
Patch Clamp Technique ◽  
Reverse Mode

The Ca2+-activated Cl− current [ I Cl(Ca)] contributes to the repolarization of the cardiac action potential under physiological conditions. I Cl(Ca) is known to be primarily activated by Ca2+release from the sarcoplasmic reticulum (SR). L-type Ca2+ current [ I Ca(L)] represents the major trigger for Ca2+ release in the heart. Recent evidence, however, suggests that Ca2+ entry via reverse-mode Na+/Ca2+exchange promoted by voltage and/or Na+ current ( I Na) may also play a role. The purpose of this study was to test the hypothesis that I Cl(Ca) can be induced by I Na in the absence of I Ca(L). Macroscopic currents and Ca2+transients were measured using the whole cell patch-clamp technique in rabbit ventricular myocytes loaded with Indo-1. Nicardipine (10 μM) abolished I Ca(L)at a holding potential of −75 mV as tested in Na+-free external solution. In the presence of 131 mM external Na+and in the absence of I Ca(L), a 4-aminopyridine-resistant transient outward current was recorded in 64 of 81 cells accompanying a phasic Ca2+ transient. The current reversed at −42.0 ± 1.3 mV ( n = 6) and at +0.3 ± 1.4 mV ( n = 6) with 21 and 141 mM of internal Cl−, respectively, similar to the predicted reversal potential with low intracellular Cl− concentration ([Cl−]i) (−47.8 mV) and high [Cl−]i(−1.2 mV). Niflumic acid (100 μM) inhibited the current without affecting the Ca2+ signal ( n = 8). Both the current and Ca2+ transient were abolished by 10 mM caffeine ( n = 6), 10 μM ryanodine ( n = 3), 30 μM tetrodotoxin ( n = 9), or removal of extracellular Ca2+( n = 6). These properties are consistent with those of I Cl(Ca)previously described in mammalian cardiac myocytes. We conclude that 1) I Cl(Ca) can be recorded in the absence of I Ca(L), and 2) I Na-induced SR Ca2+ release mechanism is also present in the rabbit heart and may play a physiological role in activating the Ca2+-sensitive membrane Cl− conductance.

scholarly journals Evidence That the Product of the Human X-Linked Cgd Gene, Gp91-phox, Is a Voltage-Gated H+ Pathway

1999 ◽  
Vol 114 (6) ◽  
pp. 771-786 ◽  
Author(s):  
Lydia M. Henderson ◽  
Robert W. Meech
Keyword(s):  
Cell Membrane ◽  
Time Course ◽  
Lucifer Yellow ◽  
Chinese Hamster ◽  
Reversal Potential ◽  
Patch Clamp Technique ◽  
Pipette Solution ◽  
Whole Cell ◽  
Histidine Residues ◽  
Voltage Gated

Expression of gp91-phox in Chinese hamster ovary (CHO91) cells is correlated with the presence of a voltage-gated H+ conductance. As one component of NADPH oxidase in neutrophils, gp91-phox is responsible for catalyzing the production of superoxide (O2·2). Suspensions of CHO91 cells exhibit arachidonate-activatable H+ fluxes (Henderson, L.M., G. Banting, and J.B. Chappell. 1995. J. Biol. Chem. 270:5909–5916) and we now characterize the electrical properties of the pathway. Voltage-gated currents were recorded from CHO91 cells using the whole-cell configuration of the patch-clamp technique under conditions designed to exclude a contribution from ions other than H+. As in other voltage-gated proton currents (Byerly, L., R. Meech, and W. Moody. 1984. J. Physiol. 351:199–216; DeCoursey, T.E., and V.V. Cherny. 1993. Biophys. J. 65:1590–1598), a lowered external pH (pHo) shifted activation to more positive voltages and caused the tail current reversal potential to shift in the manner predicted by the Nernst equation. The outward currents were also reversibly inhibited by 200 μM zinc. Voltage-gated currents were not present immediately upon perforating the cell membrane, but showed a progressive increase over the first 10–20 min of the recording period. This time course was consistent with a gradual shift in activation to more negative potentials as the pipette solution, pH 6.5, equilibrated with the cell contents (reported by Lucifer yellow included in the patch pipette). Use of the pH-sensitive dye 2′7′ bis-(2-carboxyethyl)-5(and 6) carboxyfluorescein (BCECF) suggested that the final intracellular pH (pHi) was ∼6.9, as though pHi was largely determined by endogenous cellular regulation. Arachidonate (20 μM) increased the amplitude of the currents by shifting activation to more negative voltages and by increasing the maximally available conductance. Changes in external Cl− concentration had no effect on either the time scale or the appearance of the currents. Examination of whole cell currents from cells expressing mutated versions of gp91-phox suggest that: (a) voltage as well as arachidonate sensitivity was retained by cells with only the NH2-terminal 230 amino acids, (b) histidine residues at positions 111, 115, and 119 on a putative membrane-spanning helical region of the protein contribute to H+ permeation, (c) histidine residues at positions 111 and 119 may contribute to voltage gating, (d) the histidine residue at position 115 is functionally important for H+ selectivity. Mechanisms of H+ permeation through gp91-phox include the possible protonation/deprotonation of His-115 as it is exposed alternatively to the interior and exterior faces of the cell membrane (see Starace, D.M., E. Stefani, and F. Bezanilla. 1997. Neuron. 19:1319–1327) and the transfer of protons across an “H-X-X-X-H-X-X-X-H” motif lining a conducting pore.

Segment-specific effects of FMRFamide on membrane properties of heart interneurons in the leech

1995 ◽  
Vol 74 (4) ◽  
pp. 1485-1497 ◽  
Author(s):  
J. Schmidt ◽  
S. Gramoll ◽  
R. L. Calabrese
Keyword(s):  
Outward Current ◽  
Membrane Conductance ◽  
Membrane Properties ◽  
Inward Current ◽  
Specific Effects ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
Conductance Increase

1. The effects of Phe-Met-Arg-Phe (FMRF)amide (10(-6) M) on membrane properties of heart interneurons in the third, fourth, and fifth segmental ganglia [HN(3), HN(4), and HN(5) cells, respectively] of the leech were studied using discontinuous current-clamp and single-electrode voltage-clamp techniques. FMRFamide was focally applied onto the soma of the cell under investigation. 2. Application of FMRFamide depolarized HN(3) and HN(4) cells by evoking an inward current. These responses were subject to pronounced desensitization. The inward currents evoked by application of FMRFamide were associated with an increase in membrane conductance and appeared to be voltage dependent. Currents were enhanced at more depolarized potentials. 3. The responsiveness of the HN(3) and HN(4) cells was not affected when the Ca2+ concentration in the bath saline was reduced from normal (1.8 mM) to 0.1 mM. The depolarizing response on application of FMRFamide was blocked when Co2+ was substituted for Ca2+. 4. HN(3) and HN(4) cells did not respond to FMRFamide application in Na(+)-free solution. Inward currents were largely reduced when bath saline with 30% of the normal Na+ concentration was used. When Li+ was substituted for Na+ in the saline, application of FMRFamide still evoked depolarizing responses in HN(3) and HN(4) cells. 5. We conclude that focal application of FMRFamide onto the somata of HN(3) and HN(4) cells evokes a voltage-dependent inward current, carried largely by Na+. 6. Focal application of FMRFamide onto somata of HN(5) cells hyperpolarized these cells by activating a voltage-dependent outward current. 7. HN(5) cells were loaded with Cl- until inhibitory postsynaptic potentials carried by Cl- reversed. Cl(-)-loaded cells still responded with a hyperpolarization when FMRFamide was applied onto their somata. Therefore the outward current evoked by FMRFamide appears to be mediated by a K+ conductance increase. 8. Application of FMRFamide onto the somata of HN(5) cells enhanced outward currents that were evoked by depolarizing voltage steps from a holding potential of -45 mV. 9. We conclude that the hyperpolarizing response of HN(5) cells to focal application of FMRFamide onto their somata is the result of an up-regulation of a voltage-dependent K+ current.

scholarly journals Outward current in single smooth muscle cells of the guinea pig taenia coli.

1989 ◽  
Vol 93 (3) ◽  
pp. 551-564 ◽  
Author(s):  
Y Yamamoto ◽  
S L Hu ◽  
C Y Kao
Keyword(s):  
Guinea Pig ◽  
Time Constant ◽  
Time Course ◽  
Reversal Potential ◽  
Outward Current ◽  
Enzymatic Digestion ◽  
Taenia Coli ◽  
Physiological Conditions ◽  
Dependent Component ◽  
Voltage Dependent

In single myocytes of the guinea pig taenia coli, dispersed by enzymatic digestion, the late outward current is carried by K+. It has both a Ca2+-activated component and a voltage-dependent component which is resistant to external Co2+. The reversal potential is -84 mV, and the channel(s) for it are highly selective to K+. At 33 degrees C, the activation follows n2 kinetics, with a voltage-dependent time constant of 10.6 ms at 0 mV, which shortens to 1.7 ms at +70 mV. Deactivation follows a single-exponential time course, with a voltage-dependent time constant of 11 ms at -50 mV, which lengthens to 33 ms at -20 mV. During a 4.5-s maintained depolarization, IK inactivates, most of it into two exponential components, but there is a small noninactivating residue. It is surmised that during an action potential under physiological conditions, there is sufficient IK to cause repolarization.

scholarly journals The light-sensitive conductance of hyperpolarizing invertebrate photoreceptors: a patch-clamp study.

1994 ◽  
Vol 103 (6) ◽  
pp. 939-956 ◽  
Author(s):  
M P Gomez ◽  
E Nasi
Keyword(s):  
Single Channel ◽  
Light Stimulus ◽  
Divalent Cations ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Conductance ◽  
Resting Potential ◽  
Light Stimulation ◽  
Positive Direction ◽  
Single Channel Currents

Tight-seal recording was employed to investigate membrane currents in hyperpolarizing ciliary photoreceptors enzymatically isolated from the eyes of the file clam (Lima scabra) and the bay scallop (Pecten irradians). These two organisms are unusual in that their double retinas also possess a layer of depolarizing rhabdomeric cells. Ciliary photoreceptors from Lima have a rounded soma, 15-20 microns diam, and display a prominent bundle of fine processes up to 30 microns long. The cell body of scallop cells is similar in size, but the ciliary appendages are modified, forming small spherical structures that protrude from the cell. In both species light stimulation at a voltage near the resting potential gives rise to a graded outward current several hundred pA in amplitude, accompanied by an increase in membrane conductance. The reversal potential of the photocurrent is approximately -80 mV, and shifts in the positive direction by approximately 39 mV when the concentration of extracellular K is increased from 10 to 50 mM, consistent with the notion that light activates K-selective channels. The light-activated conductance increases with depolarization in the physiological range of membrane voltages (-30 to -70 mV). Such outward rectification is greatly reduced after removal of divalent cations from the superfusate. In Pecten, cell-attached recordings were also obtained; in some patches outwardly directed single-channel currents could be activated by light but not by voltage. The unitary conductance of these channels was approximately 26 pS. Solitary ciliary cells also gave evidence of the post stimulus rebound, which is presumably responsible for initiating the "off" discharge of action potentials at the termination of a light stimulus: in patches containing only voltage-dependent channels, light stimulation suppressed depolarization-induced activity, and was followed by a strong burst of openings, directly related to the intensity of the preceding photostimulation.

Channels involved in transient currents unmasked by removal of extracellular calcium in cardiac cells

2002 ◽  
Vol 282 (5) ◽  
pp. H1879-H1888 ◽  
Author(s):  
Regina Macianskiene ◽  
Francesco Moccia ◽  
Karin R. Sipido ◽  
Willem Flameng ◽  
Kanigula Mubagwa
Keyword(s):  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Monovalent Cation ◽  
Cardiac Cells ◽  
Time Dependent ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
High Concentrations ◽  
Low Sensitivity

In cardiac cells that lack macroscopic transient outward K+ currents ( I to), the removal of extracellular Ca2+ can unmask “ I to-like” currents. With the use of pig ventricular myocytes and the whole cell patch-clamp technique, we examined the possibility that cation efflux via L-type Ca2+channels underlies these currents. Removal of extracellular Ca2+ and extracellular Mg2+ induced time-independent currents at all potentials and time-dependent currents at potentials greater than −50 mV. Either K+ or Cs+ could carry the time-dependent currents, with reversal potential of +8 mV with internal K+ and +34 mV with Cs+. Activation and inactivation were voltage dependent [Boltzmann distributions with potential of half-maximal value ( V 1/2) = −24 mV and slope = −9 mV for activation; V 1/2 = −58 mV and slope = 13 mV for inactivation]. The time-dependent currents were resistant to 4-aminopyridine and to DIDS but blocked by nifedipine at high concentrations (IC50 = 2 μM) as well as by verapamil and diltiazem. They could be increased by BAY K-8644 or by isoproterenol. We conclude that the I to-like currents are due to monovalent cation flow through L-type Ca2+ channels, which in pig myocytes show low sensitivity to nifedipine.

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