Microelectrode Voltage Clamp: The Cardiac Purkinje Fiber

1985 ◽  
pp. 171-189 ◽  
Author(s):  
Robert S. Kass ◽  
Paul B. Bennett
Keyword(s):  
Voltage Clamp ◽  
Purkinje Fiber

A re-examination of late outward plateau currents of cardiac Purkinje fibers

1985 ◽  
Vol 249 (1) ◽  
pp. H108-H121
Author(s):  
J. M. Jaeger ◽  
W. R. Gibbons
Keyword(s):  
Action Potential ◽  
Voltage Clamp ◽  
Critical Role ◽  
Membrane Current ◽  
Purkinje Fiber ◽  
Purkinje Fibers ◽  
Outward Currents ◽  
Cardiac Purkinje Fibers

Two outward currents, IX1 and IX2, are thought to be activated by depolarization of the Purkinje fiber. One of these, IX1, is presently believed to play a critical role in repolarization of the action potential. The IX currents were originally analyzed in voltage-clamp experiments in sheep Purkinje fibers. These experiments were designed to minimize interference by other currents, and it was assumed that changes of the net current were produced entirely by the IX currents. We have tried to repeat the original experiments and the analysis that led to acceptance of the existence and roles of the IX currents, without success. Moreover, tests of how membrane current should behave if the IX current hypothesis is correct did not give satisfactory results. Our data suggest the original conclusions about IX1 and IX2 may need substantial revision.

scholarly journals ACTION OF ACETYLCHOLINE ON THE PURKINJE FIBER STUDIED BY VOLTAGE CLAMP TECHNIQUE

1970 ◽  
Vol 20 (2) ◽  
pp. 155-166 ◽  
Author(s):  
Toyomi SANO ◽  
Yutaka IIDA ◽  
Masayasu HIRAOKA
Keyword(s):  
Voltage Clamp ◽  
Purkinje Fiber ◽  
Voltage Clamp Technique ◽  
Clamp Technique

Characterization of Transport Activity of SLC11 Transporters in Xenopus laevis Oocytes by Fluorophore Quenching

2021 ◽  
pp. 247255522110041
Author(s):  
Raffaella Cinquetti ◽  
Francesca Guia Imperiali ◽  
Salvatore Bozzaro ◽  
Daniele Zanella ◽  
Francesca Vacca ◽  
...  
Keyword(s):  
Xenopus Laevis ◽  
Voltage Clamp ◽  
Expression System ◽  
Peptide Transporter ◽  
Xenopus Laevis Oocytes ◽  
Substrate Uptake ◽  
Transport Activity ◽  
Experimental Conditions ◽  
Metal Transporters ◽  
Electrode Voltage

Membrane proteins are involved in different physiological functions and are the target of pharmaceutical and abuse drugs. Xenopus laevis oocytes provide a powerful heterologous expression system for functional studies of these proteins. Typical experiments investigate transport using electrophysiology and radiolabeled uptake. A two-electrode voltage clamp is suitable only for electrogenic proteins, and uptake measurements require the existence of radiolabeled substrates and adequate laboratory facilities. Recently, Dictyostelium discoideum Nramp1 and NrampB were characterized using multidisciplinary approaches. NrampB showed no measurable electrogenic activity, and it was investigated in Xenopus oocytes by acquiring confocal images of the quenching of injected fluorophore calcein. This method is adequate to measure the variation in emitted fluorescence, and thus transporter activity indirectly, but requires long experimental procedures to collect statistically consistent data. Considering that optimal expression of heterologous proteins lasts for 48–72 h, a slow acquiring process requires the use of more than one batch of oocytes to complete the experiments. Here, a novel approach to measure substrate uptake is reported. Upon injection of a fluorophore, oocytes were incubated with the substrate and the transport activity measured, evaluating fluorescence quenching in a microplate reader. The technique permits the testing of tens of oocytes in different experimental conditions simultaneously, and thus the collection of significant statistical data for each batch, saving time and animals. The method was tested with different metal transporters (SLC11), DMT1, DdNramp1, and DdNrampB, and verified with the peptide transporter PepT1 (SLC15). Comparison with traditional methods (uptake, two-electrode voltage clamp) and with quenching images acquired by fluorescence microscopy confirmed its efficacy.

Epileptiform activity in the hippocampus produced by tetraethylammonium

1990 ◽  
Vol 64 (4) ◽  
pp. 1077-1088 ◽  
Author(s):  
P. A. Rutecki ◽  
F. J. Lebeda ◽  
D. Johnston
Keyword(s):  
Potassium Channel ◽  
Voltage Clamp ◽  
Channel Blocker ◽  
Mossy Fiber ◽  
Reversal Potential ◽  
Evoked Response ◽  
Epileptiform Discharge ◽  
Extracellular Potassium ◽  
Potassium Channel Blocker ◽  
Epileptiform Discharges

1. The epileptiform discharges in the CA3 region of the rat hippocampal slice produced by bath application of the potassium channel blocker tetraethylammonium (TEA) were investigated. The effects of a convulsant (5 mM) and subconvulsant (0.5 mM) concentration of TEA on the mossy fiber-evoked synaptic currents were studied by the use of voltage-clamp techniques to determine whether TEA, like 4-aminopyridine (4-AP), another potassium channel blocker and convulsant, increased both inhibitory and excitatory components of the synaptic response. 2. At extracellular potassium concentrations of 2.5 mM, TEA (5 mM) was found to produce spontaneously occurring epileptiform discharges that could be recorded extracellularly. The intracellular correlate of the epileptiform discharge, the paroxysmal depolarizing shift (PDS), could be reversed in polarity by depolarizing the membrane and was associated with a large increase in membrane conductance. These results suggest that a synaptically mediated potential underlies the generation of the epileptiform discharge. 3. The reversal potential for the PDS was dependent on the time, relative to the extracellularly recorded field discharge, at which the measurement was made. In current clamp the mean reversal potential of the PDS measured at the midpoint of the extracellular discharge was -3.3 +/- 2.9 (SE) mV (n = 9). The reversal potential of the PDS was considerably more negative when measured either before or after the midpoint of the extracellular discharge, suggesting the presence of an inhibitory synaptic component. In voltage clamp similar results were obtained and a large conductance change was found to be associated with the PDS. These results suggest that the synaptic conductance associated with the PDS has both inhibitory and excitatory components. 4. TEA increased significantly the mossy fiber-evoked, early-inhibitory conductance. A convulsant concentration (5 mM) increased the conductance measured 15 ms after the stimulus from 39.7 +/- 8.7 to 87.2 +/- 8.0 nS (n = 6). The reversal potential associated with the conductance depolarized from -68.3 +/- 3.4 to -58.3 +/- 4.0 mV after 5 mM TEA. A subconvulsant concentration of TEA (0.5 mM) also increased the conductance of the mossy fiber-evoked response at 15 ms after the stimulus from 49.5 +/- 3.1 to 63.1 +/- 6.1 nS (n = 4) without an associated shift in reversal potential. 5. The late-inhibitory component of the mossy fiber-evoked response, when present, was increased by 5 mM TEA and unchanged by 0.5 mM TEA. 6. The excitatory mossy fiber-evoked synaptic current was studied in the presence of picrotoxin and was found to be increased and prolonged by 5 mM TEA.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Two-Microelectrode Voltage Clamp of Xenopus Oocytes: Voltage Errors and Compensation for Local Current Flow

1999 ◽  
Vol 77 (4) ◽  
pp. 1980-1991 ◽  
Author(s):  
W. Baumgartner ◽  
L. Islas ◽  
F.J. Sigworth
Keyword(s):  
Voltage Clamp ◽  
Xenopus Oocytes ◽  
Current Flow ◽  
Local Current
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