scholarly journals Properties of tetraethylammonium ion-resistant K+ channels in the photoreceptor membrane of the giant barnacle.

1981 ◽  
Vol 77 (6) ◽  
pp. 629-646 ◽  
Author(s):  
D R Edgington ◽  
A E Stuart
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Cardiac Glycosides ◽  
Time Course ◽  
Photoreceptor Membrane ◽  
K Channels ◽  
Na Pump ◽  
Tetraethylammonium Ion ◽  
Electrogenic Na Pump ◽  
Time Courses

After the offset of illumination, barnacle photoreceptors undergo a large hyperpolarization that lasts seconds or minutes. We studied the mechanisms that generate this afterpotential by recording afterpotentials intracellularly from the medial photoreceptors of the giant barnacle Balanus nubilus. The afterpotential has two components with different time-courses: (a) an earlier component due to an increase in conductance to K+ that is not blocked by extracellular tetraethylammonium ion (TEA+) or 3-aminopyridine (3-AP) and (b) a later component that is sensitive to cardiac glycosides and that requires extracellular K+, suggesting that it is due to an electrogenic Na+ pump. The K+ conductance component increases in amplitude with increasing CA++ concentration and is inhibited by extracellular Co++; the Co++ inhibition can be overcome by increasing the Ca++ concentration. Thus, the K+ conductance component is Ca++ dependent. An afterpotential similar to that evoked by a brief flash of light is generated by depolarization with current in the dark and by eliciting Ca++ action potentials in the presence of TEA+ in the soma, axon, or terminal regions of the photoreceptor. The action potential undershoot is generated by an increase in conductance to K+ that is resistant to TEA+ and 3-AP and inhibited by Co++. The similarity in time-course and pharmacology of the hyperpolarization afterpotentials elicited by (a) a brief flash of light, (b) depolarization with current, and (c) an action potential indicates that Ca++-dependent K+ channels throughout the photoreceptor membrane are responsible for all three hyperpolarizing events.

Time course of postnatal changes in rat heart action potential and in transient outward current is different

1994 ◽  
Vol 267 (3) ◽  
pp. H1157-H1166 ◽  
Author(s):  
G. M. Wahler ◽  
S. J. Dollinger ◽  
J. M. Smith ◽  
K. L. Flemal
Keyword(s):  
Action Potential ◽  
Rat Heart ◽  
Action Potentials ◽  
Time Course ◽  
Outward Current ◽  
Transient Outward Current ◽  
Papillary Muscles ◽  
Isolated Cells ◽  
Time Courses ◽  
Action Potential Shortening

The rat ventricular action potential shortens after birth. The contribution of increases in the transient outward current (Ito) to postnatal action potential shortening was assessed by measuring Ito in isolated cells and by determining the effect of 2 mM 4-aminopyridine (4-AP) on the action potentials of papillary muscles. 4-AP had no effect on 1-day action potential duration at 25% repolarization (APD25), and 1-day cells had little Ito. In 8- to 10-day muscles, 4-AP caused a small, but significant, increase in APD25. Ito increased slightly between day 1 and days 8-10, but this increase was not significant. Most of the increase in Ito (79%) and in the response to 4-AP (64%) occurred between days 8-10 and adult; however, approximately 75% of the APD25 shortening took place by days 8-10. Thus, while Ito may contribute to repolarization in late neonatal and adult cells, the different time courses of action potential shortening and increases in Ito suggest that changes in Ito are unlikely to be responsible for most of the postnatal action potential shortening.

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.

Effect of Several Cations on Transmembrane Potentials of Cardiac Muscle

1956 ◽  
Vol 186 (2) ◽  
pp. 317-324 ◽  
Author(s):  
Brian F. Hoffman ◽  
E. E. Suckling
Keyword(s):  
Action Potential ◽  
Cardiac Muscle ◽  
Action Potentials ◽  
Time Course ◽  
Pacemaker Activity ◽  
Transmembrane Potentials ◽  
High K ◽  
Intracellular Microelectrodes ◽  
Simultaneous Decrease ◽  
Low K

The effects of changes in the extracellular concentrations of Ca, K and Mg on the transmembrane resting and action potentials of single fibers of the auricle, ventricle and specialized conducting system of the dog heart have been studied by means of intracellular microelectrodes. With respect to Ca, the three tissues exhibit quite different sensitivities. Changes in concentration of this ion alter the time course of the action potential recorded from auricle and ventricle but have little effect on the action potential configuration of the Purkinje fiber. In the latter tissue, on the other hand, pacemaker activity is most strongly enhanced by Ca depletion and excitability is lost at Ca concentrations permitting normal propagation in papillary muscle. The effect of K on the resting transmembrane potential is dependent on the simultaneous Ca concentration. The interrelationship is such that the depolarizing effect of high K is decreased by elevated Ca and the depolarization produced by low K is diminished by low levels of Ca. Changes in the concentration of Mg have little effect on the transmembrane potentials of cardiac muscle unless the level of Ca is low. Under this condition a simultaneous decrease in Mg gives rise to a marked prolongation of the action potential duration of both auricle and ventricle. Some evidence for the basic similarity of the processes underlying repolarization in these three tissues is presented and it is thought the normally encountered differences in their action potentials may be related to the sensitivity of each tissue to extracellular Ca.

Posttetanic hyperpolarization produced by electrogenic Na(+)-K+ pump in lizard axons impaled near their motor terminals

1993 ◽  
Vol 70 (5) ◽  
pp. 1874-1884 ◽  
Author(s):  
K. Morita ◽  
G. David ◽  
J. N. Barrett ◽  
E. F. Barrett
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Time Course ◽  
Input Resistance ◽  
Peak Amplitude ◽  
Resting Potential ◽  
Tetanic Stimulation ◽  
Train Duration ◽  
Consistent Change ◽  
Nodal Voltage

1. The hyperpolarization that follows tetanic stimulation was recorded intra-axonally from the internodal region of intramuscular myelinated motor axons. 2. The peak amplitude of the posttetanic hyperpolarization (PTH) that followed stimulation at 20-100 Hz for < or = 35 s increased with increasing train duration, reaching a maximum of 22 mV. PTH decayed over a time course that increased from tens to hundreds of seconds with increasing train duration. For a given frequency of stimulation the time integral of PTH was proportional to the number of stimuli in the train, averaging 3-4 mV.s per action potential. 3. Ouabain (0.1-1 mM) and cyanide (1 mM) depolarized the resting potential and abolished PTH. Tetanic stimulation in ouabain was followed by a slowly decaying depolarization (probably due to extra-axonal K+ accumulation) whose magnitude and duration increased as the duration of the train increased. 4. Axonal input resistance showed no consistent change during PTH in normal solution but increased during PTH in the presence of 3 mM Cs+ (which blocks axonal inward rectifier currents). 5. PTH was abolished when bath Na+ was replaced by Li+ or choline. PTH persisted after removal of bath Ca2+ and addition of 2 mM Mn2+. 6. Removal of bath K+ abolished the PTH recorded after brief stimulus trains and greatly reduced the duration of PTH recorded after longer stimulus trains. 7. A brief application of 10 mM K+, which normally depolarizes axons, produced a ouabain-sensitive hyperpolarization in axons bathed in K(+)-free solution. 8. These observations suggest that in these myelinated axons PTH is produced mainly by activation of an electrogenic Na(+)-K(+)-ATPase, rather than by changes in K+ permeability or transmembrane [K+] gradients. This conclusion is supported by calculations showing agreement between estimates of Na+ efflux/impulse based on PTH measurements and estimates of Na+ influx/impulse based on nodal voltage-clamp measurements. Pump activity also appears to contribute to the resting potential. 9. The stimulus intensity required to initiate a propagating action potential increased during PTH but decreased during the posttetanic depolarization recorded in ouabain. Thus changes in axonal excitability after tetanic stimulation correlate with changes in the posttetanic membrane potential. 10. Action potentials that propagated during PTH had a larger peak amplitude and were followed by a larger and longer depolarizing afterpotential than action potentials elicited at the resting potential. This enhancement of the depolarizing afterpotential is consistent with previous reports of an increased superexcitable period after action potentials evoked during PTH.

Contribution of Na+/Ca2+ exchange to action potential of human atrial myocytes

1996 ◽  
Vol 271 (3) ◽  
pp. H1151-H1161 ◽  
Author(s):  
A. Benardeau ◽  
S. N. Hatem ◽  
C. Rucker-Martin ◽  
B. Le Grand ◽  
L. Mace ◽  
...  
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Time Course ◽  
Significant Proportion ◽  
Type A ◽  
Plateau Phase ◽  
Type B ◽  
Atrial Myocytes ◽  
Human Atrial Myocytes ◽  
Delayed Afterdepolarizations

The Ca2+ dye indo 1 was used to record internal Ca2+ (Cai) transients in order to investigate the role of the Na+/Ca2+ exchange current (INa/Ca) in whole cell patch-clamped human atrial myocytes After the activation of the L-type Ca2+ current by test pulses (20 ms) at +20 mV, a tail current (I(tail)) was activated at a holding potential of -80 mV with a density of -1.29 +/- 0.06 pA/pF. The time course of I(tail) followed that of Cai transients I(tail) was suppressed by dialyzing cells with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, applying 5 mM caffeine, or substituting external Na+ with Li+, indicating that this current was mainly generated by INa/Ca. Two types of action potential were recorded: type A, which is characterized by a narrow early plateau followed by a late low plateau phase, and type B, which is characterized by a small initial peak followed by a prolonged high plateau phase. Type B action potentials were found in larger cells than type A action potentials (membrane capacitance 81.8 +/- 4.5 and 122.4 +/- 7.0 pF in types A and B, respectively, P < 0.001). Substitution of external Na+ with Li+ shortened the late plateau of the type A action potential and the prolonged plateau of the type B action potential. Suppression of Cai transients by caffeine shortens the late part of both types of action potentials, whereas its lengthening effect on the initial phase of action potentials can result from several different mechanisms. The beat-to-beat dependent relationship between Cai transients and action potentials could be mediated by Ina/Ca- Delayed afterdepolarizations were present in a significant proportion of atrial myocytes in our experimental conditions. They were reversibly suppressed by Li+ substitution for Na+, suggesting that they are generated by INa/Ca. We conclude that INa/Ca plays a major role in the development of action potentials and delayed afterdepolarizations in isolated human atrial myocytes.

scholarly journals Two Components of the Cardiac Action Potential

1969 ◽  
Vol 54 (5) ◽  
pp. 607-635 ◽  
Author(s):  
Antonio Paes de Carvalho ◽  
Brian Francis Hoffman ◽  
Marilene de Paula Carvalho
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Time Course ◽  
Slow Component ◽  
Slow Inward Current ◽  
Equilibrium Potential ◽  
Slow Phase ◽  
Positive Equilibrium ◽  
Cardiac Action

Transmembrane potentials recorded from the rabbit heart in vitro were displayed as voltage against time (V, t display), and dV/dt against voltage (V, V or phase-plane display). Acetylcholine was applied to the recording site by means of a hydraulic system. Results showed that (a) differences in time course of action potential upstroke can be explained in terms of the relative magnitude of fast and slow phases of depolarization; (b) acetylcholine is capable of depressing the slow phase of depolarization as well as the plateau of the action potential; and (c) action potentials from nodal (SA and AV) cells seem to lack the initial fast phase. These results were construed to support a two-component hypothesis for cardiac electrogenesis. The hypothesis states that cardiac action potentials are composed of two distinct and physiologically separable "components" which result from discrete mechanisms. An initial fast component is a sodium spike similar to that of squid nerve. The slow component, which accounts for both a slow depolarization during phase 0 and the plateau, probably is dependent on the properties of a slow inward current having a positive equilibrium potential, coupled to a decrease in the resting potassium conductance. According to the hypothesis, SA and AV nodal action potentials are due entirely or almost entirely to the slow component and can therefore be expected to exhibit unique electrophysiological and pharmacological properties.

Propagation of action potentials in the dendrites of neurons from rat spinal cord slice cultures

1996 ◽  
Vol 75 (1) ◽  
pp. 154-170 ◽  
Author(s):  
M. E. Larkum ◽  
M. G. Rioult ◽  
H. R. Luscher
Keyword(s):  
Spinal Cord ◽  
Action Potential ◽  
Calcium Imaging ◽  
Action Potentials ◽  
Synaptic Activity ◽  
Rat Spinal Cord ◽  
Voltage Sensitive Dye ◽  
Single Action ◽  
Before And After ◽  
Time Courses

1. We examined the propagation of action potentials in the dendrites of ventrally located presumed motoneurons of organotypic rat spinal cord cultures. Simultaneous patch electrode recordings were made from the dendrites and somata of individual cells. In other experiments we visualized the membrane voltage over all the proximal dendrites simultaneously using a voltage-sensitive dye and an array of photodiodes. Calcium imaging was used to measure the dendritic rise in Ca2+ accompanying the propagating action potentials. 2. Spontaneous and evoked action potentials were recorded using high-resistance patch electrodes with separations of 30-423 microm between the somatic and dendritic electrodes. 3. Action potentials recorded in the dendrites varied considerably in amplitude but were larger than would be expected if the dendrites were to behave as passive cables (sometimes little or no decrement was seen for distances of > 100 microm). Because the amplitude of the action potentials in different dendrites was not a simple function of distance from the soma, we suggest that the conductance responsible for the boosting of the action potential amplitude varied in density from dendrite to dendrite and possibly along each dendrite. 4. The dendritic action potentials were usually smaller and broader and arrived later at the dendritic electrode than at the somatic electrode irrespective of whether stimulation occurred at the dendrite or soma or as a result of spontaneous synaptic activity. This is clear evidence that the action potential is initiated at or near the soma and spreads out into the dendrites. The conduction velocity of the propagating action potential was estimated to be 0.5 m/s. 5. The voltage time courses of previously recorded action potentials were generated at the soma using voltage clamp before and after applying 1 microM tetrodotoxin (TTX) over the soma and dendrites. TTX reduced the amplitude of the action potential at the dendritic electrode to a value in the range expected for dendrites that behave as passive cables. This indicates that the conductance responsible for the actively propagating action potentials is a Na+ conductance. 6. The amplitude of the dendritic action potential could also be initially reduced more than the somatic action potential using 1-10 mM QX-314 (an intracellular sodium channel blocker) in the dendritic electrode as the drug diffused from the dendritic electrode toward the soma. Furthermore, in some cases the action potential elicited by current injection into the dendrite had two components. The first component was blocked by QX-314 in the first few seconds of the diffusion of the blocker. 7. In some cells, an afterdepolarizing potential (ADP) was more prominent in the dendrite than in the soma. This ADP could be reversibly blocked by 1 mM Ni2+ or by perfusion of a nominally Ca2+-free solution over the soma and dendrites. This suggests that the back-propagating action potential caused an influx of Ca2+ predominantly in the dendrites. 8. With the use of a voltage-sensitive dye (di-8-ANEPPS) and an array of photodiodes, the action potential was tracked along all the proximal dendrites simultaneously. The results confirmed that the action potential propagated actively, in contrast to similarly measured hyperpolarizing pulses that spread passively. There were also indications that the action potential was not uniformly propagated in all the dendrites, suggesting the possibility that the distribution of Na+ channels over the dendritic membrane is not uniform. 9. Calcium imaging with the Ca2+ fluorescent indicator Fluo-3 showed a larger percentage change in fluorescence in the dendrites than in the soma. Both bursts and single action potentials elicited sharp rises in fluorescence in the proximal dendrites, suggesting that the back-propagating action potential causes a concomitant rise in intracellular calcium concentration...

scholarly journals On the effects of divalent cations and ethylene glycol-bis-(beta-aminoethyl ether) N,N,N',N'-tetraacetate on action potential duration in frog heart.

1978 ◽  
Vol 71 (1) ◽  
pp. 47-67 ◽  
Author(s):  
D J Miller ◽  
A Mörchen
Keyword(s):  
Ethylene Glycol ◽  
Action Potential ◽  
Calcium Ions ◽  
Action Potentials ◽  
Time Course ◽  
Divalent Cations ◽  
Potassium Conductance ◽  
Resting Potential ◽  
Slow Inward Current ◽  
Frog Heart

Resting and action potentials were recorded from superfused strips of frog ventricle. Reducing the bathing calcium concentration ([Ca2+]0) with or without ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA) prolongs the action potential (AP). The change in the duration of the AP extends over many minutes, but is rapidly reversed by restoring calcium ions. Other changes (e.g., in resting potential and overshoot) are, however, only more slowly reversed. Reducing [Ca2+]0 with 0.2, 2, or 5 mM EGTA produces progressively greater prolongation of AP; maximum values were well in excess of 1 min. This prolongation can be reversed by other divalent cations in EGTA (Mg2+, Sr2+) or Ca-free (Mn2+) solutions, or by acetylcholine. Barium ions increase AP duration in keeping with their known effect on potassium conductance. D600, which blocks the slow inward current in cardiac muscle, is without effect on the action potentials recorded in EGTA solutions, or on the time course and extent of the recovery to normal duration upon restoring calcium ions. It is concluded that divalent cations exert an influence on membrane potassium conductance extracellularly in frog heart. The cell membrane does not become excessively "leaky" in EGTA solutions.

scholarly journals Radial propagation of muscle action potential along the tubular system examined by potential-sensitive dyes.

1980 ◽  
Vol 76 (6) ◽  
pp. 751-762 ◽  
Author(s):  
S Nakajima ◽  
A Gilai
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Time Course ◽  
Surface Membrane ◽  
Simultaneous Recording ◽  
Conduction Delay ◽  
Muscle Action Potential ◽  
Tubular System ◽  
Intracellular Action ◽  
T System

Isolated single (Xenopus) muscle fibers were stained with a non-permeant potential-probing dye, merocyanine rhodanine (WW375) or merocyanine oxazolone (NK2367). When the fiber was massively stimulated, an absorption change (wave a), which seemed to reflect the action potential, occurred. Simultaneous recording of optical changes and intracellular action potentials revealed that the time-course of wave a was slower than the action potential: the peak of wave a was attained at 1 ms, and the peak of action potential was reached at 0.5 ms after the stimulation. This difference suggests that wave a represents the potential changes of the whole tubular membrane and the surface membrane, whereas the action potential represents a surface potential change. This idea was substantiated by recording absorption signals preferentially from the surface membrane by recording the absorption changes at the edge of the fiber. Wave a obtained by this method was as quick as the intracellular action potential. The value of radial conduction velocity of action potential along the T system, calculated by comparing the action potential with wave a, was 6.4 cm/s at 24.5 degrees C, in fair agreement with González-Serratos (1971. J. Physiol. [Lond.]. 212:777-799). The shape of wave a suggests the existence of an access delay (a conduction delay at the orifice of the T system) of 130 microseconds.

scholarly journals Simultaneous monitoring of changes in magnesium and calcium concentrations in frog cut twitch fibers containing antipyrylazo III.

1989 ◽  
Vol 93 (4) ◽  
pp. 585-608 ◽  
Author(s):  
M Irving ◽  
J Maylie ◽  
N L Sizto ◽  
W K Chandler
Keyword(s):  
Action Potential ◽  
Voltage Clamp ◽  
Rate Constant ◽  
Time Course ◽  
Average Rate ◽  
Wavelength Dependence ◽  
Phenol Red ◽  
Single Action ◽  
Ph Indicators ◽  
Time Courses

Antipyrylazo III was introduced into frog cut twitch fibers (17-19 degrees C) by diffusion. After action potential stimulation, the change in indicator absorbance could be resolved into two components that had different time courses and wavelength dependences. The first component was early and transient and due to an increase in myoplasmic free [Ca] (Maylie, J., M. Irving, N.L. Sizto, and W.K. Chandler, 1987, Journal of General Physiology, 89:83-143). The second component, usually measured at 590 nm (near the isosbestic wavelength for Ca), developed later than the Ca transient and returned towards baseline about 100 times more slowly. Although the wavelength dependence of this component is consistent with an increase in either free [Mg] or pH, its time course is clearly different from that of the signals obtained with the pH indicators phenol red and 4',5'-dimethyl-5-(and -6-) carboxyfluorescein, suggesting that it is mainly due to an increase in free [Mg]. After a single action potential in freshly prepared cut fibers that contained 0.3 mM antipyrylazo III, the mean peak amplitude of delta A (590) would correspond to an increase in free [Mg] of 47 microM if all the signal were due to a change in [Mg] and all the intracellular indicator reacted with Mg as in cuvette calibrations. With either repetitive action potential stimulation or voltage-clamp depolarization, the delta A (590) signal continued to develop throughout the period when free [Ca] was elevated and then recovered to within 40-90% of the prestimulus baseline with an average rate constant between 0.5 and 1.0 s-1. With prolonged voltage-clamp depolarization, both the amplitude and rate of development of the delta A(590) signal increased with the amplitude of the depolarization and appeared to saturate at levels corresponding to an increase in free [Mg] of 0.8-1.4 mM and a maximum rate constant of 3-4 s-1, respectively. These results are consistent with the idea that the delta A(590) signal is primarily due to changes in myoplasmic free [Mg] produced by a change in the Mg occupancy of the Ca,Mg sites on parvalbumin that results from the Ca transient.

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