scholarly journals Changes in external Na induce a membrane current related to the Na-Ca exchange in cesium-loaded frog heart cells.

1984 ◽  
Vol 84 (2) ◽  
pp. 201-220 ◽  
Author(s):  
D Mentrard ◽  
G Vassort ◽  
R Fischmeister
Keyword(s):  
Membrane Potential ◽  
Outward Current ◽  
Current Amplitude ◽  
Frog Heart ◽  
Heart Cells ◽  
Ca Ions ◽  
Standard Solution ◽  
A Current ◽  
K Currents ◽  
Intact Heart

The effects of transient alterations in Nao were investigated under voltage clamp conditions in frog heart cells previously loaded with Cs. Tetrodotoxin and Cs were used to inhibit Na and K currents. On applying a Na-poor solution (39.2 mM), an outward current was generated during both depolarizations and hyperpolarizations. The current amplitude described a U-shaped function of the membrane potential. On reapplying the standard solution after 15 min equilibration, an inward current was then induced that exhibited a bell-shaped function of the membrane potential. Current amplitude was sensitive to the external Ca concentration. Increasing pHi by 10 mM NH4Cl enhanced this current, while the internal acidification that occurred on switching back to the control solution greatly reduced it. Variations in the amplitude of this current during repetitive stimulations or long pauses are best explained by subsequent alterations in Nai and pHi; no evidence for a time dependence was found. This current was inhibited by La3+, Co2+, and D600, and was sensitive to adriamycin, quinidine, and disopyramide; lidocaine, another local anesthetic, and nifedipine had no effect. These observations extend previous work on intact heart cells and sarcolemmal vesicles. They suggest that the Na-Ca exchange may generate a current that is outward when Ca ions are moving into the cell.

Patch-clamp study of postnatal development of CA1 neurons in rat hippocampal slices: membrane excitability and K+ currents

1992 ◽  
Vol 68 (1) ◽  
pp. 55-69 ◽  
Author(s):  
I. Spigelman ◽  
L. Zhang ◽  
P. L. Carlen
Keyword(s):  
Membrane Potential ◽  
Patch Clamp ◽  
Action Potentials ◽  
Hippocampal Slices ◽  
Outward Current ◽  
Resting Potential ◽  
Resting Membrane Potential ◽  
Ca1 Neurons ◽  
Outward Currents ◽  
K Currents

1. The postnatal development of membrane properties and outward K+ currents in CA1 neurons in rat hippocampal slices was studied with the use of whole-cell patch-clamp techniques. 2. Neurons at all postnatal ages (2-30 days; P2-30) were capable of generating tetrodotoxin (TTX)-sensitive action potentials in response to intracellular injection of depolarizing current pulses. There was a gradual increase in the amplitude and a decrease in the duration of these action potentials with age. Stable values for spike duration were reached by P15, whereas spike amplitude increased until P20-25. In P2-5 neurons, the duration of action potentials was greatly prolonged by depolarization from the resting membrane potential, indicating a weak spike repolarizing mechanism at depolarized potentials. In contrast, the duration of spikes evoked in P20-30 neurons was not affected by similar changes in the membrane potential. 3. Application of tetraethylammonium (TEA, 10 mM) had no effect on the duration of spikes in P3-5 neurons, whereas application of 4-aminopyridine (4-AP, 2 mM) produced large increases in spike duration. In contrast, the duration of spikes in P26 neurons was greatly increased after TEA application, whereas 4-AP had smaller effects on spike duration in these neurons. 4. The input resistance and membrane time constant decreased with age from P2 to P15. The values for both parameters were considerably greater than those reported with conventional intracellular recording electrodes in the immature hippocampus. The resting membrane potential became more hyperpolarized with age. When the recording pipettes contained KCl (140 mM), the resting potential of P3-4 neurons was 34 mV depolarized compared with resting potentials observed with potassium gluconate-filled pipettes. Only a 13-mV change in resting potential was observed during similar comparisons in P27-28 neurons. 5. Outward currents activated by depolarization were examined with the use of voltage-clamp techniques in P2-30 neurons. In P2-5 cells, a small, slowly inactivating outward current was evoked with depolarizing commands from holding potentials near -50 mV. By preceding the depolarizing commands with a hyperpolarizing prepulse, an additional early transient outward current was evoked. The sustained and transient outward currents were separated by their kinetic properties and their sensitivity to cobalt (Co2+), TEA, and 4-AP.(ABSTRACT TRUNCATED AT 400 WORDS)

Slow inactivation of a TEA-sensitive K current in acutely isolated rat thalamic relay neurons

1991 ◽  
Vol 66 (4) ◽  
pp. 1316-1328 ◽  
Author(s):  
J. R. Huguenard ◽  
D. A. Prince
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Outward Current ◽  
Resting Potential ◽  
Transient Outward Current ◽  
Voltage Range ◽  
Voltage Dependent ◽  
Kinetics Of ◽  
K Currents ◽  
Relay Neurons

1. Voltage-gated K currents were studied in relay neurons (RNs) acutely isolated from somatosensory (VB) thalamus of 7- to 14-day-old rats. In addition to a rapidly activated, transient outward current, IA, depolarizations activated slower K+ currents, which were isolated through the use of appropriate ionic and pharmacological conditions and measured via whole-cell voltage-clamp. 2. At least two slow components of outward current were observed, both of which were sensitive to changes in [K+]o, as expected for K conductances. The first, IK1, had an amplitude that was insensitive to holding potential and a relatively small conductance of 150 pS/pF. It was blocked by submillimolar levels of tetraethylammonium [TEA, 50%-inhibitory concentration (IC50 = 30 microM)] and 4-aminopyridine (4-AP, 40 microM). In the absence of intracellular Ca2+ buffering, the amplitude of IK1 was both larger and dependent on holding potential, as expected for a Ca(2+)-dependent current. Replacement of [Ca2+]o by Co2+ reduced IK1, although the addition of Cd2+ to Ca(2+)-containing solutions had no effect. 3. The second component, IK2, had a normalized conductance of 2.0 nS/pF and was blocked by millimolar concentrations of TEA (IC50 = 4 mM) but not by 4AP. The kinetics of IK2 were analogous to (but much slower than) those of IA in that both currents displayed voltage-dependent activation and voltage-independent inactivation. IK2 was not reduced by the addition of Cd2+ to Ca(2+)-containing solutions or by replacement of Ca2+ by Co2+. 4. IK2 had a more depolarized activation threshold than IA and attained peak amplitude with a latency of approximately 100 ms at room temperature. IK2 decay was nonexponential and could be described as the sum of two components with time constants (tau) near 1 and 10 s. 5. IK2 was one-half steady-state inactivated at a membrane potential of -63 mV, near the normal resting potential for these cells. The slope factor of the Boltzman function describing steady-state inactivation was 13 mV-1, which indicates that IK2 varies in availability across a broad voltage range between -100 and -20 mV. 6. Activation kinetics of IK2 were voltage dependent, with peak latency shifting from 300 to 50 ms in the voltage range -50 to +30 mV. Deinactivation and deactivation were also voltage dependent, in contrast to inactivation, which showed little dependence on membrane potential. Increase in temperature sped the kinetics of IK2, with temperature coefficient (Q10) values near 3 for activation and inactivation. Heating increased the amplitude of IK2 with a Q10 value near 2.(ABSTRACT TRUNCATED AT 400 WORDS)

Creation of a hard microrelief on a titanium surface processed by microplasma discharges with a current amplitude of 200 A and pulse duration of 20 ms

2012 ◽  
Vol 38 (13) ◽  
pp. 1105-1112 ◽  
Author(s):  
V. A. Ivanov ◽  
M. E. Konyzhev ◽  
L. I. Kuksenova ◽  
V. G. Lapteva ◽  
M. S. Alekseeva ◽  
...  
Keyword(s):  
Pulse Duration ◽  
Titanium Surface ◽  
Current Amplitude ◽  
A Current

Analysis of caffeine action in single trabeculae of the frog heart

1981 ◽  
Vol 213 (1192) ◽  
pp. 303-324 ◽  
Keyword(s):  
Calcium Influx ◽  
Test Procedure ◽  
Frog Heart ◽  
Heart Cells ◽  
Store Depletion ◽  
Perfusion Chamber ◽  
Rapid Perfusion ◽  
The One ◽  
Intracellular Action ◽  
External Calcium

Effects of caffeine on contractile tension and on intracellular action and resting potentials were examined in single frog heart trabeculae suspended in a rapid perfusion chamber. Trabeculae from atria responded more readily than those from ventricles and were therefore studied in greater detail. Both the contracture and twitch responses, the one obtained at high (>10 mM), the other at low (<10mM) caffeine concentrations, consisted of a transient tension rise followed by a maintained phase of lower, but still enhanced, tension. The hypothesis was tested that the transient response is due to the release of calcium from the sarcoplasmic reticulum (s.r.), whereas the maintained tension results from enhanced calcium influx through the cell surface. Support for these ideas was obtained by examining the response to step changes of external calcium and caffeine concentrations, applied in various combinations, simultaneously and in sequence. It also emerged that the effects on twitch tension of calcium derived from (a) s.r. discharge and ( b) influx are additive, to a first approximation. A test procedure for monitoring the s.r. store content was evolved to follow the accumulation of s.r. calcium after a preceding depletion. The results obtained, and others, suggest that the s.r. calcium pump can be operative in atrial heart cells and capable, after store depletion, of reabsorbing up to some 40 % of calcium activating a twitch, the remainder being, presumably, extruded from the cells.

scholarly journals Extracellular Hco3− Dependence of Electrogenic Na/Hco3 Cotransporters Cloned from Salamander and Rat Kidney

2000 ◽  
Vol 115 (5) ◽  
pp. 533-546 ◽  
Author(s):  
Irina I. Grichtchenko ◽  
Michael F. Romero ◽  
Walter F. Boron
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Xenopus Oocytes ◽  
Rat Kidney ◽  
Outward Current ◽  
Membrane Vesicles ◽  
Disulfonic Acid ◽  
Ambystoma Tigrinum ◽  
Ph Titration ◽  
Electrode Voltage

We studied the extracellular [HCOabstract 3 −] dependence of two renal clones of the electrogenic Na/HCO3 cotransporter (NBC) heterologously expressed in Xenopus oocytes. We used microelectrodes to measure the change in membrane potential (ΔVm) elicited by the NBC cloned from the kidney of the salamander Ambystoma tigrinum (akNBC) and by the NBC cloned from the kidney of rat (rkNBC). We used a two-electrode voltage clamp to measure the change in current (ΔI) elicited by rkNBC. Briefly exposing an NBC-expressing oocyte to HCOabstract 3 −/CO2 (0.33–99 mM HCOabstract 3−, pHo 7.5) elicited an immediate, DIDS (4,4-diisothiocyanatostilbene-2,2-disulfonic acid)-sensitive and Na+-dependent hyperpolarization (or outward current). In ΔVm experiments, the apparent Km for HCOabstract 3− of akNBC (10.6 mM) and rkNBC (10.8 mM) were similar. However, under voltage-clamp conditions, the apparent Km for HCOabstract 3− of rkNBC was less (6.5 mM). Because it has been reported that SOabstract 3=/HSO abstract 3− stimulates Na/HCO3 cotransport in renal membrane vesicles (a result that supports the existence of a COabstract 3= binding site with which SOabstract 3= interacts), we examined the effect of SOabstract 3=/HSO abstract 3− on rkNBC. In voltage-clamp studies, we found that neither 33 mM SOabstract 4= nor 33 mM SOabstract 3 =/HSOabstract 3− substantially affects the apparent Km for HCO abstract 3−. We also used microelectrodes to monitor intracellular pH (pHi) while exposing rkNBC-expressing oocytes to 3.3 mM HCOabstract 3 −/0.5% CO2. We found that SO abstract 3=/HSOabstract 3 − did not significantly affect the DIDS-sensitive component of the pHi recovery from the initial CO2 -induced acidification. We also monitored the rkNBC current while simultaneously varying [CO2]o, pHo, and [COabstract 3=]o at a fixed [HCOabstract 3−]o of 33 mM. A Michaelis-Menten equation poorly fitted the data expressed as current versus [COabstract 3=]o . However, a pH titration curve nicely fitted the data expressed as current versus pHo. Thus, rkNBC expressed in Xenopus oocytes does not appear to interact with SOabstract 3 =, HSOabstract 3−, or COabstract 3=.

Na+, K+ and Ca2+ currents in identified leech neurones in culture

1989 ◽  
Vol 141 (1) ◽  
pp. 1-20
Author(s):  
R. R. Stewart ◽  
J. G. Nicholls ◽  
W. B. Adams
Keyword(s):  
Minor Component ◽  
Outward Current ◽  
Membrane Properties ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Channel Blockers ◽  
Sensory Neurones ◽  
K Current ◽  
The Individual ◽  
K Currents

1. Na+, K+ and Ca2+ currents have been measured by voltage-clamp in Retzius (R), anterior pagoda (AP) and sensory (pressure, touch and nociceptive) cells dissected from the central nervous system (CNS) of the leech. These cells maintain their distinctive membrane properties and action potential configurations in culture. Currents carried by the individual ions were analysed by the use of channel blockers and by their kinetics. Since the cells are isopotential they can be voltage-clamped effectively. 2. Depolarization, as expected, gave rise to an early inward Na+ current followed by a delayed outward K+ current. In Na+-free medium containing tetraethylammonium (TEA+), and in the presence of 4-aminopyridine (4-AP), inward Ca2+ currents were revealed that inactivated slowly and were blocked by Cd2+ and Mn2+. 3. Na+ and Ca2+ currents were similar in their characteristics in R. AP and sensory neurones. In contrast, K+ currents showed marked differences. Three principal K+ currents were identified. These differed in their time courses of activation and inactivation and in their responses to Ca2+ channel blockers. 4. K+ currents of the A-type (IA) activated and inactivated rapidly, were not affected by Ca2+ channel blockers and were eliminated by steady-state inactivation at holding potentials of −30 mV. A-type K+ currents were found in AP cells and as a minor component of the outward current in R cells. A Ca2+-activated K+ current (IC), that inactivated more slowly and was reduced by Ca2+ channel blockers, constituted the major outward current in R cells. The third K+ current resembled the delayed rectifier currents (IK1 and IK2) of squid axons with slow activation and inactivation kinetics. Such currents were found in R cells and in the sensory neurones (T, P and N). 5. The principal differences in membrane properties of identified leech neurones can be explained in terms of the numbers of Na+ channels and the distinctive kinetics of K+ channels in each type of cell.

Influence of anomalous rectifier activation on afterhyperpolarizations of neurons from cat sensorimotor cortex in vitro

1988 ◽  
Vol 59 (2) ◽  
pp. 468-481 ◽  
Author(s):  
P. C. Schwindt ◽  
W. J. Spain ◽  
W. E. Crill
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Sensorimotor Cortex ◽  
Model Parameters ◽  
Fast Decay ◽  
Time Constants ◽  
Anomalous Rectifier ◽  
Betz Cells ◽  
K Currents

1. Large neurons from layer V of cat sensorimotor cortex (Betz cells) were studied to determine the influence of the anomalous rectifier current (IAR) on slow afterhyperpolarizations (AHPs). The neurons were examined using intracellular recording and single-microelectrode voltage clamp in an in vitro brain slice preparation. 2. A faster medium-duration AHP (mAHP) and slower AHP (sAHP) followed repetitive firing (22, 23). The amplitude of the mAHP often increased or remained constant during membrane potential hyperpolarization. The membrane potential trajectory resulting solely from IAR activation was similar to the mAHP. 3. Postrepetitive firing voltage clamp was used to measure directly slowly decaying K+ currents (IK) and IAR at different membrane potentials. IK exhibited both a fast and slow decay. The time constants of the fast decay of IK and IAR activation were similar. IAR increased with hyperpolarization or raised extracellular K+ concentration [( K+]o), whereas both the fast and slow components of IK reversed or nulled near -100 mV and behaved as pure K+ currents in response to raised [K+]o. 4. To determine the precise contribution of IK and IAR to the AHP waveform, theoretical AHPs were computed using a quantitative model based on voltage-clamp measurements. The calculated AHPs were qualitatively similar to measured AHPs. The amplitude of the mAHP showed little change with hyperpolarization because of the increasing dominance of IAR at more negative membrane potentials. The sAHP was little affected by IAR activation. 5. Several model parameters subject to biological variation among Betz cells were varied in the calculations to determine their importance in the AHP waveform. With IK parameters held constant, the amplitude and time course of the mAHP depended on resting potential, membrane time constant, the kinetics of the anomalous rectifier conductance (GAR), and the maximum value of GAR. IAR activation could result in a biphasic AHP even when the fast decay of IK was omitted from the calculations. 6. A wider variation of model parameters revealed behavior that may be relevant to other neurons. Certain values of membrane or IAR activation time constants resulted in a monophasic AHP even when the fast decay of IK was present. The decay of a biphasic AHP could reflect either the onset of IAR or the fast decay of IK, depending on the relative value of their time constants. Procedures are outlined to discriminate between these possibilities using current clamp methods.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of reduced Na gradient on electrical activity in isolated bovine and feline ventricular myocytes

1988 ◽  
Vol 66 (2) ◽  
pp. 222-232 ◽  
Author(s):  
Magda Horackova ◽  
Andrzej Beresewicz ◽  
Gerrit Isenberg
Keyword(s):  
Electrical Activity ◽  
Ventricular Myocytes ◽  
Ionic Current ◽  
Outward Current ◽  
Free Solution ◽  
Initial Part ◽  
Inward Current ◽  
Ca Inward Current ◽  
Sudden Decrease ◽  
K Currents

We have studied changes in electrical activity resulting from abrupt alterations of the Na gradient, using ventricular myocytes isolated from feline and bovine hearts. Attempting to investigate the ionic current possibly generated by Na–Ca exchange, we studied the effects of the changes in [Na]o in the presence of 20 mM CsCl to inhibit K currents. To facilitate the effect of Cs, we also used a K-free solution and a patch electrode filled with 150 mM cesium glutamate. The application of 20 mM Nao resulted in hyperpolarization and the action potential duration was reduced. Under voltage clamp, 20 or 45 mM Nao generated an outward current at all membrane potentials investigated. The initial part (100–200 ms) of this current was only partially inhibited by 5 mM NiCl2 which is known to fully block the Ca inward current. However, the outward current generated by the reduced [Na]o was fully inhibited by 20 mM MnCl2 (which presumably inhibits Na–Ca exchange). Our observations extend the work on multicellular cardiac preparations indicating that the outward current elicited by a sudden decrease in Na gradient could be generated by Na–Ca exchange. Although the characteristics of this outward current support certain concepts of the Na–Ca exchange in cardiac muscle, we cannot at present exclude a contribution of other membrane current(s).

Cellular and subcellular mechanisms of cardiac pacemaker oscillations

1979 ◽  
Vol 81 (1) ◽  
pp. 205-215
Author(s):  
R. W. Tsien ◽  
R. S. Kass ◽  
R. Weingart
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Surface Membrane ◽  
Cardiac Pacemaker ◽  
Oscillatory Activity ◽  
Purkinje Fibre ◽  
Pacemaker Activity ◽  
Heart Cells ◽  
Control Loop ◽  
Internal Oscillation

Rhythmic oscillations in the membrane potential of heart cells are important in normal cardiac pacemaker activity as well as cardiac arrhythmias. Two fundamentally different mechanisms of oscillatory activity can be distinguished at the cellular and subcellular level. The first mechanism, referred to as a surface membrane oscillator, can be represented by a control loop in which membrane potential changes evoke delayed conductance changes and vice versa. Since the surface membrane potential is a key variable within the control loop, the oscillation can be interrupted at any time by holding the membrane potential constant with a voltage clamp. This mode of oscillation seems to describe spontaneous pacemaker activity in the primary cardiac pacemaker (sinoatrial node) as well as other regions (Purkinje fibre, atrial or ventricular muscle). In all tissues studied so far, the pacemaker depolarization is dominated by the slow shutting-off of an outward current, largely carried by potassium ions. The second mechanism can be called an internal oscillator since it depends upon a subcellular rhythm generator which is largely independent from the surface membrane. Under voltage clamp, the existence of the internal oscillation is revealed by the presence of oscillations in membrane conductance or contractile force which occur even though the membrane potential is held fixed. The two oscillatory mechanisms are not mutually exclusive; the subcellular mechanism can be preferentially enhanced in any given cardiac cell by conditions which elevate intracellular calcium. Such conditions include digitalis intoxication, high Cao, low Nao, low or high Ko, cooling, or rapid stimulation. Several lines of evidence suggest that the subcellular mechanism involves oscillatory variations in myoplasmic calcium, probably due to cycles of Ca uptake and release by the sarcoplasmic reticulum. The detailed nature of the Cai oscillator and its interaction with the surface membrane await further investigation.

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