Correlation of light-induced changes in retinal extracellular potassium concentration with c-wave of the electroretinogram

1976 ◽  
Vol 39 (5) ◽  
pp. 1117-1133 ◽  
Author(s):  
B. Oakley ◽  
D. G. Green
Keyword(s):  
Time Course ◽  
Potassium Concentration ◽  
Action Spectrum ◽  
Extracellular Potassium ◽  
Threshold Curve ◽  
Photoreceptor Layer ◽  
Extracellular Potassium Concentration ◽  
Increment Threshold ◽  
Induced Changes ◽  
Pigment Epithelial Cells

1. Double-barrel, potassium-specific microelectrodes have been used to measure light-induced transient changes in [K+]o in the frog eye cup preparation. These changes in [K+]o have been termed the potassioretinogram (KRG). 2. The KRG consists of two components: a rapid increase in [K+]o in the proximal retina and a slow decrease in [K+]o in the distal retina. 3. The KRG decrease has the rhodopsin action spectrum, is maximal in the photoreceptor layer, persists after aspartate treatment, and has an increment threshold curve which saturates at moderate background intensities. The rhodopsin rods are, therefore, most likely the only neurons which generate this ionic change, although the Muller (glial) cells may also be involved in this process. 4. The KRG decrease has the same time course as the c-wave of the electroretinogram for all variations in the stimulus parameters, including intensity, duration, and chromaticity. 5. It is suggested that the c-wave may be produced by the pigment epithelial cells as they hyperpolarize in response to the decrease in [K+]o around the photoreceptors.

scholarly journals Effects of the rod receptor potential upon retinal extracellular potassium concentration.

1979 ◽  
Vol 74 (6) ◽  
pp. 713-737 ◽  
Author(s):  
B Oakley ◽  
D G Flaming ◽  
K T Brown
Keyword(s):  
Time Course ◽  
Potassium Concentration ◽  
Receptor Potential ◽  
Ion Concentration ◽  
Extracellular Potassium ◽  
Photoreceptor Layer ◽  
Extracellular Potassium Concentration ◽  
Wide Range ◽  
The Relationship ◽  
Toad Bufo

It has been hypothesized that the light-evoked rod hyperpolarization (the receptor potential) initiates the light-evoked decrease in extracellular potassium ion concentration, [K+]o, in the distal retina. The hypothesis was tested using the isolated, superfused retina of the toad, Bufo marinus; the receptor potential was recorded intracellularly from red rods, and [K+]o was measured in the photoreceptor layer with K+-specific microelectrodes. In support of the hypothesis, variations in stimulus irradiance or duration, or in retinal temperature, produced qualitatively similar effects on both the receptor potential and the decrease in [K+]o. A mechanism for the relationship between the receptor potential and the decrease in [K+]o was suggested by Matsuura et al. (1978. Vision Res. 18:767-775). In the dark, the passive efflux of K+ out of the rod is balanced by an equal influx of K+ fromthe Na+/K+ pump. The light-evoked rod hyperpolarization is assumed to reduce the passive efflux, with little effect on the pump. Thus, the influx will exceed the efflux, and [K+]o will decrease. Consistent with this mechanism, the largest and most rapid decrease in [K+]o was measured adjacent to the rod inner segments, where the Na+/K+ pump is most likely located; in addition, inhibition of the pump with ouabain abolished the decrease in [K]o more rapidly than the rod hyperpolarization. Based upon this mechanism, Matsuura et al. (1978) developed a mathematical model: over a wide range of stimulus irradiance, this model successfully predicts the time-course of the decrease in [K+]o, given only the time-course of the rod hyperpolarization.

Correlation Between Extracellular Focal Potentials and K+ Potentials Evoked by Primary Afferent Activity

1975 ◽  
Vol 53 (5) ◽  
pp. 912-922 ◽  
Author(s):  
K. Krnjević ◽  
M. E. Morris
Keyword(s):  
Time Course ◽  
Potassium Concentration ◽  
Extracellular Potassium ◽  
Cuneate Nucleus ◽  
Afferent Activity ◽  
Extracellular Potassium Concentration ◽  
Afferent Nerves ◽  
Focal Potentials ◽  
Constant Slope ◽  
Stimulation Of

There is a clear, positive correlation in amplitude between changes in potassium potentials (ΔEK) and focal potentials (ΔV) evoked by tetanic stimulation of afferent nerves in the cuneate nucleus and dorsal horn of cats under Dial anaesthesia or after decerebration. Data obtained with stimulations at various frequencies and intensities, or recording at different positions give a relatively constant slope of ΔV/ΔEK (varying between 0.2 and 0.6 in different experiments). These observations are fully consistent with the possibility that ΔV mainly reflects changes in extracellular potassium concentration caused by the release of K+ from active terminals. Differences in time course of ΔEK and ΔV evoked by single stimuli are a steep function of distance and therefore can be ascribed to the slowness of diffusion, without excluding the possibility of an early additional depolarizing effect by another mechanism.

scholarly journals Junctional resistance and action potential delay between embryonic heart cell aggregates.

1980 ◽  
Vol 75 (6) ◽  
pp. 633-654 ◽  
Author(s):  
D E Clapham ◽  
A Shrier ◽  
R L DeHaan
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Time Course ◽  
Potassium Concentration ◽  
Aggregate Size ◽  
Heart Cell ◽  
Extracellular Potassium ◽  
Cell Aggregates ◽  
Extracellular Potassium Concentration ◽  
Junctional Resistance

Spheroidal aggregates of embryonic chick ventricle cells were brought into contact and allowed to synchronize their spontaneous beats. Action potentials were recorded with both intracellular and extracellular electrodes. The degree of electrical interaction between the newly apposed aggregates was assessed by measuring the delay or latency (L) between the entrained action potentials, and by determining directly interaggregate coupling resistance (Rc) with injected current pulses. Aggregate size, contact area between the aggregates, and extracellular potassium concentration (Ko+) were important variables regulating the time-course of coupling. When these variables were controlled, L and Rc were found to be linearly related after beat synchrony was achieved. In 4.8 mM Ko+ L/Rc = 3.7 ms/M omega; in 1.3 mM Ko+ L/Rc = 10.1 ms/M omega. We conclude that action potential delay between heart cell aggregates can be related quantitatively to Rc.

Disorders of potassium homeostasis

2010 ◽  
pp. 3831-3845 ◽  
Author(s):  
J Firth
Keyword(s):  
Membrane Potential ◽  
Potassium Concentration ◽  
Resting Membrane Potential ◽  
Extracellular Potassium ◽  
Normal Range ◽  
Critical Determinant ◽  
Potassium Homeostasis ◽  
Extracellular Potassium Concentration

The normal range of potassium concentration in serum is 3.5 to 5.0 mmol/litre and within cells it is 150 to 160 mmol/litre, the ratio of intracellular to extracellular potassium concentration being a critical determinant of cellular resting membrane potential and thereby of the function of excitable tissues....

Theoretical analysis of parameters leading to frequency modulation along an inhomogeneous axon

1976 ◽  
Vol 39 (4) ◽  
pp. 909-923 ◽  
Author(s):  
I. Parnas ◽  
S. Hochstein ◽  
H. Parnas
Keyword(s):  
Potassium Concentration ◽  
Single Step ◽  
Repetitive Firing ◽  
Extracellular Potassium ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Extracellular Potassium Concentration ◽  
Spike Shape ◽  
Single Spike ◽  
Low Pass

1. Theoretical computations were conducted on a computer model of a segmented, nonhomogeneous axon to understand the mechanism of frequency block of conduction. 2. The model is based on the Hodgkin-Huxley equations modified in several ways to better describe the cockroach axon. We used cockroach parameters where available. 3. The increase in fiber radius was spread over a series of segments to approximate a taper. We found that a taper allows a larger overall increase in fiber diameter than a single step to be successfully passed. 4. We studied effects on a train of impulses. The modified equations included effects due to changes in extracellular potassium concentration resulting from the repetitive firing of the axon. 5. An increase in diameter which allows a single spike to pass blocks the subsequent impulses in a train at the taper if potassium concentration variability is introduced. This could explain the low-pass filter characteristics of axon constrictions. 6. Results of the model fit well with the experiemental spike shape and height. Data were computed for the refractory period and its dependence on the taper parameters.

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