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.

The electrophysiological effects of disopyramide phosphate on canine ventricular muscle and Purkinfe fibers in normal and low potassium

1978 ◽  
Vol 56 (1) ◽  
pp. 139-149 ◽  
Author(s):  
Teresa Kus ◽  
Betty I. Sasyniuk
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Time Course ◽  
Antiarrhythmic Effect ◽  
Extracellular Potassium ◽  
Ventricular Muscle ◽  
Extracellular Potassium Concentration ◽  
Course Of Action ◽  
Low K ◽  
Electrophysiological Effects

We studied the effect of lowering the extracellular potassium concentration ([K+]0) on the electrophysiological actions of disopyramide phosphate, a new antiarrhythmic drug. At low [K+]0, therapeutic concentrations of disopyramide phosphate caused significantly less depression of action potential amplitude and maximum upstroke velocity of both Purkinje fiber and ventricular muscle action potentials. The drug shifted the membrane responsiveness curve along the voltage axis to more negative membrane potentials regardless of [K+]0. However, a greater shift occurred when [K+]0 was normal. Disopyramide phosphate prolonged both action potential duration and effective refractory period in all fibers but there was consistently greater prolongation of these parameters at low [K+]0, More importantly, disopyramide phosphate altered repolarization time course of action potentials in such a way that action potentials with dissimilar durations throughout the ventricular conducting system became more equal. The drug was less effective in decreasing this disparity in action potential durations throughout the ventricles in the presence of low [K+]0. These modifications of the electrophysiological actions of disopyramide by low [K+]0 suggest that a therapeutic concentration of disopyramide might have less of an antiarrhythmic effect in the presence of hypokalemia.

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.

Sensory neurons in leech central nervous system: changes in potassium conductance an excitation threshold

1976 ◽  
Vol 39 (6) ◽  
pp. 1184-1192 ◽  
Author(s):  
W. R. Schlue
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Membrane Potential ◽  
Action Potential ◽  
Sensory Neurons ◽  
Potassium Concentration ◽  
Potassium Conductance ◽  
Extracellular Potassium ◽  
Extracellular Potassium Concentration ◽  
Accommodation Coefficients

1. The sensory neurons in the leech central nervous system differ in their accommodation to linearly rising currents. Advantage was taken of these differences to study the ionic mechanism of accommodation in single pairs of N (noxious), P (pressure), and T (touch) cells. 2. Nonlinearities in membrane-potential changes and current-voltage relationships with square-wave and ramp currents are more pronounced in P and T cells than in N cells. The accommodation coefficients increase in conditions that reflect this delayed rectification. When rectification is absent, the accommodation coefficients depart from unity only slightly or not at all. 3. Accommodation coefficients remain unchanged when half of the chloride in the bathing medium is replaced by sulfate. Accommodation coefficients become greater when the extracellular potassium concentration is reduced from 4 to 0 mM, and decrease when the concentration is raised to 8 mM. The membrane potential changes by only a few millivolts. 4. As extracellular potassium concentration is increased, the action potential is lengthened and the maximal rate of fall of the action potential is reduced. With concentrations greater than 4 mM these relationships are linear, but depart from linearity at lower concentrations. The amplitude of the undershoot decreases linearly as the extracellular potassium concentration increases from 4 to 16 mM, and increases non-linearly at concentrations below 4 mM. 5. The rapid accommodation of leech neurons is based primarily on an increased potassium conductance. The possibility is considered that concentration changes like those produced experimentally may occur naturally, affecting integrative processes in the central nervous system.

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 Positive and Negative Inotropic Effects of Elevated Extracellular Potassium Level on Mammalian Ventricular Muscle

1972 ◽  
Vol 60 (3) ◽  
pp. 351-365 ◽  
Author(s):  
Frederic Kavaler ◽  
Paul M. Hyman ◽  
Robert B. Lefkowitz
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Time Course ◽  
Potassium Level ◽  
Positive Inotropic Effect ◽  
Potassium Concentration ◽  
Inotropic Effect ◽  
Extracellular Potassium ◽  
Ventricular Muscle ◽  
Inotropic Effects

The effect of moderate elevation in extracellular potassium concentration (up to 12 mM) on contraction of cat ventricular muscle was examined. Isometric force development was recorded from eight excised trabeculae and from six coronary-perfused in situ papillary muscle preparations. Contraction in the steady state was variably affected, sometimes decreasing monotonically, sometimes remaining unchanged, with increasing potassium level. In 11 of these 14 preparations, the steady state was preceded by a transient period in which the contraction was augmented. In addition, eight excised trabeculae were used in an experimental arrangement designed to distinguish between inotropic effects caused by potassium-induced alterations in the action potential and other, more direct, effects of this ion on contraction. The negative inotropic effect is attributable to a potassium-induced reduction in the amplitude and/or duration of the action potential plateau. The positive inotropic effect was found in experimental arrangements where effects of the potassium-rich medium on action potential time-course were effectively "buffered." The positive inotropic effect thus depends on the presence of the elevated potassium concentration and can occur independently of effects on the action potential time-course.

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.

Calcium Dynamics and Compartmentalization in Leech Neurons

2005 ◽  
Vol 94 (6) ◽  
pp. 4430-4440 ◽  
Author(s):  
Sofija Andjelic ◽  
Vincent Torre
Keyword(s):  
Information Processing ◽  
Action Potential ◽  
Action Potentials ◽  
Time Course ◽  
Ccd Camera ◽  
Calcium Dynamics ◽  
Single Action ◽  
Single Action Potential ◽  
Calcium Indicator ◽  
Mechanosensory Neurons

Calcium dynamics in leech neurons were studied using a fast CCD camera. Fluorescence changes (Δ F/ F) of the membrane impermeable calcium indicator Oregon Green were measured. The dye was pressure injected into the soma of neurons under investigation. Δ F/ F caused by a single action potential (AP) in mechanosensory neurons had approximately the same amplitude and time course in the soma and in distal processes. By contrast, in other neurons such as the Anterior Pagoda neuron, the Annulus Erector motoneuron, the L motoneuron, and other motoneurons, APs evoked by passing depolarizing current in the soma produced much larger fluorescence changes in distal processes than in the soma. When APs were evoked by stimulating one distal axon through the root, Δ F/ F was large in all distal processes but very small in the soma. Our results show a clear compartmentalization of calcium dynamics in most leech neurons in which the soma does not give propagating action potentials. In such cells, the soma, while not excitable, can affect information processing by modulating the sites of origin and conduction of AP propagation in distal excitable processes.

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