Calcium/Sodium Binding Competition in the Gating of Light-Activated Membrane Conductance Studied by Voltage Clamp Technique in Limulus Ventral Nerve Photoreceptor

1985 ◽  
Vol 40 (3-4) ◽  
pp. 278-291 ◽  
Author(s):  
H. Stieve ◽  
M. Pflaum ◽  
J. Klomfaß ◽  
H. Gaube
Keyword(s):  
Voltage Clamp ◽  
Voltage Dependence ◽  
Divalent Cations ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
Light Response ◽  
Membrane Current ◽  
Voltage Clamp Technique ◽  
Clamp Technique ◽  
Conductance Increase

The membrane current vs. voltage dependence was measured in Limulus ventral nerve photo­receptors at various external Ca2+ and Na+ concentrations, using the voltage clamp technique. Lowering the external concentration of the divalent cations Ca2+ and Mg+ to < 1 μmol/l by adding EDTA causes 1)the light-induced transient conductance increase to disappear and 2)the reversal potential of the membrane current in the dark to shift to a positive value between + 10 and + 20 mV. This value is about the same as the (VrevJD), reversal potential of the total light current under normal ionic conditions. If the external Na+ is lowered to 50 mmol/1 (i.e. 10% of the normal concentration) simultaneously with the lowering of the divalent cation concentration described above, the light response is not abolished and VrevJD is shifted less. The extent of this antagonism depends on the sodium sub­stitute; it is stronger if choline is used instead of lithium. Lowering of sodium alone to 50 mmol/1, in a saline containing normal Ca2+ and Mg2+ concen­trations, does not change the membrane dark current vs. voltage curve and so VrevJD is not altered; Vrev⊿JL, the reversal potential of the light-induced current, however, is reduced by 10 mV (from +20 to +10 mV). This reduction in Vrev⊿JL can be accounted for by the reduction of the sodium gradient across the cell membrane. Raising the external Ca2+ concentration to 40 or 100 mmol/l has no conspicuous effect on the membrane current vs. voltage dependence and the gating of the light-induced conductance in­crease. The results are consistent with our working hypothesis that the gating of the light-activated ion channels in Limulus photoreceptor is controlled by negative binding sites for which calcium- and sodium ions compete with antagonistic actions.

Measurement of GABA-evoked conductance changes of lobster muscle fibres by a three-microelectrode voltage clamp technique

1982 ◽  
Vol 215 (1200) ◽  
pp. 343-364 ◽  
Keyword(s):  
Voltage Clamp ◽  
Surface Membrane ◽  
Membrane Conductance ◽  
Effective Capacity ◽  
Muscle Fibres ◽  
Voltage Clamp Technique ◽  
Clamp Technique ◽  
Conductance Changes ◽  
Access Resistance ◽  
Tubular Membranes

The effective membrane conductance and capacity of lobster muscle fibres was measured by a three-intracellular-microelectrode voltage clamp technique. Conductance values agreed well with those determined under current clamp, by means of the ‘short’ cable equations. Reversible increases in conductance evoked by γ-aminobutyric acid (GABA) were reflected by differences (∆V) in electrotonic potential amplitude recorded at the centre, and midway between the centre and fibre end respectively. GABA dose-conductance curves derived from cable theory or from ∆V measurements were virtually identical. The effective capacity ( c eff ), determined from the area beneath the ‘ on ’ ∆V capacity transient, yielded values of the membrane time constant consistently lower than those obtained by the graphical method of E. Stefani & A.B. Steinbach ( J. Physiol ., London . 203, 383-401 (1969)); one possible explanation for this discrepancy is discussed. In the presence of GABA, the effective capacity was reduced in a dose-related manner. The results were interpreted in terms of an equivalent circuit in which surface membrane was arranged in parallel with cleft-tubular membrane of finite conductance, charged through an access resistance. GABA was thought to be decreasing c eff by selectively increasing the conductance of the cleft-tubular membranes.

Discrete Threshold and Repetitive Responses in the Squid Axon Under ‘Voltage-Clamp’

1958 ◽  
Vol 193 (2) ◽  
pp. 301-308 ◽  
Author(s):  
I. Tasaki ◽  
A. F. Bak
Keyword(s):  
Voltage Clamp ◽  
Membrane Depolarization ◽  
Membrane Current ◽  
Potential Difference ◽  
Squid Axon ◽  
Voltage Clamp Technique ◽  
Clamp Technique

By using the so-called voltage-clamp technique, records were obtained indicating the presence of undulatory or oscillatory membrane current under fixed potential difference between the internal and external electrodes. This oscillatory membrane current was observed only when rectangular membrane depolarization was in the range between 15 and about 35 mv. The amplitude of the oscillatory membrane current was of the order of 1 ma/cm2. The oscillatory membrane current disappeared suddenly when the depolarizing clamping pulse was reduced below the ‘threshold.’ Various sources of artefact were examined.

Adjusting the neurons models in neuromimetic ICs using the voltage-clamp technique

2008 ◽  
Author(s):  
Sylvain Saighi ◽  
Laure Buhry ◽  
Yannick Bornat ◽  
Gilles N'Kaoua ◽  
Jean Tomas ◽  
...  
Keyword(s):  
Voltage Clamp ◽  
Voltage Clamp Technique ◽  
Clamp Technique

scholarly journals Membrane properties of a barnacle photoreceptor examined by the voltage clamp technique

1970 ◽  
Vol 208 (2) ◽  
pp. 385-413 ◽  
Author(s):  
H. Mack Brown ◽  
S. Hagiwara ◽  
H. Koike ◽  
R. M. Meech
Keyword(s):  
Voltage Clamp ◽  
Membrane Properties ◽  
Voltage Clamp Technique ◽  
Clamp Technique

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.

scholarly journals Two Light-Induced Processes in the Photoreceptor Cells of Limulus Ventral Eye

1971 ◽  
Vol 58 (5) ◽  
pp. 544-561 ◽  
Author(s):  
J. E. Lisman ◽  
J. E. Brown
Keyword(s):  
Voltage Clamp ◽  
Photoreceptor Cell ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
Photoreceptor Cells ◽  
Negative Slope ◽  
Induced Current ◽  
Positive Slope ◽  
Current Voltage ◽  
Lower Slope

The dark-adapted current-voltage (I-V) curve of a ventral photoreceptor cell of Limulus, measured by a voltage-clamp technique, has a high slope-resistance region more negative than resting voltage, a lower slope-resistance region between resting voltage and zero, and a negative slope-resistance region more positive than 0 v. With illumination, we find no unique voltage at which there is no light-induced current. At the termination of illumination, the I-V curve changes quickly, then recovers very slowly to a dark-adapted configuration. The voltage-clamp currents during and after illumination can be interpreted to arise from two separate processes. One process (fast) changes quickly with change in illumination, has a reversal potential at +20 mv, and has an I-V curve with positive slope resistance at all voltages. These properties are consistent with a light-induced change in membrane conductance to sodium ions. The other process (slow) changes slowly with changes in illumination, generates light-activated current at +20 mv, and has an I-V curve with a large region of negative slope resistance. The mechanism of this process cannot as yet be identified.

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