Ionic Determinants of Spontaneous Activity in Clusters of Cultured Cardiac Cells from Newborn Rats

1975 ◽  
Vol 53 (6) ◽  
pp. 1209-1213
Author(s):  
O. F. Schanne ◽  
C. Rivard ◽  
G. Doyon
Keyword(s):  
Spontaneous Activity ◽  
Cardiac Cells ◽  
Slow Inward Current ◽  
Heart Cells ◽  
Newborn Rats ◽  
Sodium Potassium ◽  
Inward Current ◽  
Cell Clusters ◽  
Beating Rate ◽  
Rat Heart Cells

The spontaneous activity of cell clusters derived from ventricle cells of newborn rats was studied using a recording television microscope. The influence of varying concentrations of sodium, potassium, calcium, tetrodotoxin (TTX), and that of 2 mM MnCl2 was tested. The spontaneous activity of the cell clusters persisted in TTX but it was abolished by Mn. The beating rate increased when [Ca]0 and [Na]0 were changed from 0.3 mM to 3.0 mM and from 30 mM to 75 mM; it decreased with a change of [Na]0 from 75 mM to 142 mM. It is concluded that electrogenesis in these cells is determined by a slow inward current and that these cell clusters are comparable in their behavior to very young embryonic rat heart cells or cells of the rabbit sinoauricular node.

Factors Involved in the Loss of Spontaneous Contractile and Electrical Activity in Clusters of Cultured Cardiac Cells

1972 ◽  
Vol 50 (6) ◽  
pp. 523-532 ◽  
Author(s):  
O. F. Schanne
Keyword(s):  
Electrical Activity ◽  
Spontaneous Activity ◽  
Cardiac Cells ◽  
Pacemaker Activity ◽  
Newborn Rats ◽  
Cell Clusters ◽  
A Cell ◽  
Enzyme Pattern ◽  
Membrane Changes ◽  
Increasing Temperature

Beating cell clusters were obtained by trypsinization from hearts of newborn rats. Spontaneous activity ceased after several weeks while the cultures were still proliferating. Experiments were performed to identify the physiological determinant causing cessation of spontaneous activity. (a) Cell clusters having lost their spontaneous activity responded to extracellular stimulation. (b) Reduction of [K]o by 50% increased the number of beating cell clusters by 40%; doubling [K]o reduced the number of beating cell clusters by 49%. (c) Cell clusters which were in the process of losing their ability to contract spontaneously needed a progressively increasing temperature to induce spontaneous activity. These results suggest (1) that the pacemaker mechanism fails first when a cell cluster loses its spontaneous activity and (2) that shortly before the cluster fails to contract spontaneously, it requires more energy to maintain pacemaker activity because of possible structural membrane changes or changes in the enzyme pattern of the cells.

Separation of Na-Ca exchange and transient inward currents in heart cells

1987 ◽  
Vol 253 (5) ◽  
pp. H1330-H1333
Author(s):  
Y. Shimoni ◽  
W. Giles
Keyword(s):  
Sodium Current ◽  
Single Cells ◽  
Cardiac Cells ◽  
Slow Inward Current ◽  
Heart Cells ◽  
Inward Current ◽  
Inward Currents ◽  
Isolated Cardiac Cells ◽  
Fast Sodium Current ◽  
External K

Enzymatically dispersed single cells from rabbit ventricle were voltage clamped using the suction pipette method to investigate whether in isolated cardiac cells a recently described slow inward current (IEX) due to the electrogenic Na+-dependent Ca2+ extrusion also underlies a transient inward current (ITI), which can trigger certain cardiac arrhythmias. The cells were held at -40 mV to inactivate the fast sodium current. After depolarizing pulses (to 0 or +10 mV for 50 to 200 ms), slow inward "tail" currents were consistently recorded. Previous results indicate that this tail current IEX is generated by the Na+-Ca2+ exchanger. After loading the cells with Ca2+ by blocking the Na+-K+ pump [either with strophanthidin (10(-5) M) treatment or by reducing external K+ to 1 mM or less], ITIS appeared. These were usually spontaneous but occasionally were time locked to the clamp pulses. It was possible to separate IEX and ITI by a variety of methods. These include the following. 1) Different stimulation protocols; repolarizing to more negative potentials augmented IEX and decreased or eliminated ITI. Increasing the rate of stimulation diminished IEX and increased ITI. 2) Pharmacological methods; adding BaCl2 (0.5-2.0 mM) or caffeine (5-10 mM) decreased IEX but abolished ITI. The findings suggest that different mechanisms regulate these two currents.

Membrane resistance increases when automaticity develops in explanted rat heart cells

1990 ◽  
Vol 258 (1) ◽  
pp. H145-H152 ◽  
Author(s):  
O. F. Schanne ◽  
M. Lefloch ◽  
B. Fermini ◽  
E. Ruiz-Petrich
Keyword(s):  
Spontaneous Activity ◽  
Action Potentials ◽  
Ventricular Myocytes ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Heart Cells ◽  
Membrane Capacity ◽  
Rat Heart Cells ◽  
Specific Membrane

We compared the passive electrical properties of isolated ventricular myocytes (resting potential -65 mV, fast action potentials, and no spontaneous activity) with those of 2- to 7-day-old cultured ventricle cells from neonatal rats (resting potential -50 mV, slow action potentials, and presence of spontaneous activity). In myocytes the specific membrane capacity was 0.99 microF/cm2, and the specific membrane resistance increased from 2.46 k omega.cm2 at -65 mV to 7.30 k omega.cm2 at -30 mV. In clusters, the current-voltage relationships measured under current-clamp conditions showed anomalous rectification and the input resistance decreased from 1.05 to 0.48 M omega when external K+ concentration was increased from 6 to 100 mM. Using the model of a finite disk we determined the specific membrane resistance (12.9 k omega.cm2), the effective membrane capacity (17.8 microF/cm2), and the lumped resistivity of the disk interior (1,964 omega.cm). We conclude that 1) the voltage dependence of the specific membrane resistance cannot completely explain the membrane resistance increase that accompanies the appearance of spontaneous activity; 2) a decrease of the inwardly rectifying conductance (gk1) is mainly responsible for the increase in the specific membrane resistance and depolarization; and 3) approximately 41% of the inward-rectifying channels are electrically silent when spontaneous activity develops in explanted ventricle cells.

FMRFamide effects on membrane properties of heart cells isolated from the leech, Hirudo medicinalis

1992 ◽  
Vol 67 (2) ◽  
pp. 280-291 ◽  
Author(s):  
K. J. Thompson ◽  
R. L. Calabrese
Keyword(s):  
Isolated Heart ◽  
Muscle Cells ◽  
Membrane Properties ◽  
Slow Inward Current ◽  
Heart Cells ◽  
Linear Component ◽  
Inward Current ◽  
Isolated Heart Cells ◽  
Voltage Dependent ◽  
K Currents

1. The effects of the cardioactive peptide FMRFamide were tested on enzymatically dissociated muscle cells isolated from hearts of the leech. These cells were normally quiescent, with resting potentials near -60 mV. 2. Superfusion of FMRFamide induced a strong depolarization in isolated heart cells (e.g., greater than 40 mV with 10(-6) M FMRFamide). The depolarization was maintained in the continued presence of peptide and persisted long after its removal. Less frequently, FMRFamide superfusion elicited an episodic polarization rhythm. 3. The response of isolated heart cells to bath-applied FMRFamide showed a 1- to 2-min latency. The latency decreased with repeated applications of FMRFamide. 4. The FMRFamide response was diminished by Na+ replacement but persisted with Ca2+ channel blockade. 5. In voltage-clamped heart cells (-60 mv), superfusion of FMRFamide elicited a slow inward current with a transient and a sustained component. 6. Current-voltage (I-V) curves during FMRFamide superfusion in normal leech saline showed that FMRFamide also enhanced voltage-dependent outward currents activated at depolarized levels. 7. Under conditions in which K+ currents were substantially blocked, the FMRFamide-dependent I-V curve was net inward from -90 to +50 mV. A voltage-dependent component was blocked by Co2+ and a linear component by Na+ replacement. 8. We conclude that FMRFamide elicits a persistent inward current with a Na+ component and in addition modulates both voltage-dependent Ca2+ and K+ currents that may contribute to the normal myogenic activity of leech heart muscle cells.

Uncoupling of cardiac cells by fatty acids: structure-activity relationships

1991 ◽  
Vol 260 (3) ◽  
pp. C439-C448 ◽  
Author(s):  
J. M. Burt ◽  
K. D. Massey ◽  
B. N. Minnich
Keyword(s):  
Fatty Acids ◽  
Oleic Acid ◽  
Unsaturated Fatty Acids ◽  
Saturated Fatty Acids ◽  
Decanoic Acid ◽  
Cardiac Cells ◽  
Neonatal Rat ◽  
Heart Cells ◽  
Dependent Manner ◽  
Rat Heart Cells

The permeability and conductance of gap junctions between pairs of neonatal rat heart cells were rapidly and reversibly decreased by oleic acid in a dose- and time-dependent manner. Other unsaturated fatty acids (C-18: cis 6, 9, or 11, and C-18, 16, and 14, cis 9), saturated fatty acids (C-10, 12, and 14), and saturated fatty alcohols (C-8, 10, and 12) also caused uncoupling. The most effective compounds of the unsaturated and saturated fatty acid and saturated fatty alcohol series caused essentially complete uncoupling at comparable aqueous concentrations. However, oleic acid uncoupled cells at membrane concentrations as low as 1 mol%, whereas decanoic acid required upwards of 35 mol%. The channels that support the action potential remained functional at these same membrane concentrations. The data are discussed in terms of the possible mechanism by which these compounds cause uncoupling and the possible role of uncoupling by nonesterified free fatty acids in the initiation of arrhythmias during and after ischemic insults.

Effects of K-channel blockers, calcium, and verapamil suggest different pacemaker mechanisms in cultured neonatal rat and embryonic chick ventricle cells

1989 ◽  
Vol 67 (7) ◽  
pp. 795-800 ◽  
Author(s):  
Otto F. Schanne ◽  
L. Boutin ◽  
J. Derosiers
Keyword(s):  
Cardiac Cells ◽  
Neonatal Rat ◽  
K Channel ◽  
Chronotropic Effect ◽  
Inward Current ◽  
Diastolic Depolarization ◽  
K Current ◽  
Beating Rate ◽  
Rat Ventricle ◽  
Diastolic Potential

We compared the determinants of spontaneous activity in explanted neonatal (2-day-old) rat ventricle cells and in reaggregates derived from 15-day-old chick embryos. We studied the beating rate with an optical recording method and the underlying electrical activity with glass microelectrodes using the K current blockers cesium (Cs) and tetraethylammonium, varied Ca concentrations, and the Ca antagonist verapamil. In the rat (i) Cs increased the beating rate that was mediated by an increase in the slope of the diastolic potential, (ii) Ca increased the beating rate dramatically at low and medium concentrations to decrease it again at 8 mM Cao.2This increase in the beating rate was mediated by an increase of the slope of the diastolic depolarization. (iii) The beating rate decreased with verapamil at concentrations between 0.5 and 2.0 μM. The effects of Cs and Ca suggest that an increase in net inward current (block of IK1) underlies the positive chronotropic effect of Cs and that the pacemaker mechanism is determined by a Ca inward current or an IT1 type current modulated by variations of Cai. In the chick reaggregates (i) Cs and tetraethylammonium decreased the beating rate that was mainly brought about by a decrease in the slope of diastolic depolarization. (ii) Ca increased the beating rate but to a lesser degree than in the rat and there was no decrease of the beating rate at higher concentrations. (iii) The increase in the beating rate was not mediated by an increase in the slope of the diastolic potential but mainly by a depolarization of the maximum diastolic potential. (iv) Verapamil inhibited electrogenesis before any change in the diastolic potential was evident. The negative chronotropic effect of Cs and tetraethylammonium is compatible with the notion that a voltage- and time-dependent K current was inhibited and that this current determines the pacemaker. Moreover, the Ca component of the pacemaker mechanism in explanted rat ventricle cells resembles either that of the sinoatrial node or represents triggered activity.Key words: pacemaker mechanism, cultured cardiac cells, K-channel blocker, calcium, verapamil.

Caffeine-induced current in embryonic heart cells: time course and voltage dependence

1983 ◽  
Vol 245 (3) ◽  
pp. H528-H532 ◽  
Author(s):  
W. T. Clusin ◽  
R. Fischmeister ◽  
R. L. DeHaan
Keyword(s):  
Time Course ◽  
Reversal Potential ◽  
Myocardial Cell ◽  
Slow Inward Current ◽  
Heart Cells ◽  
Induced Current ◽  
Inward Current ◽  
Current Voltage ◽  
Micron Diameter ◽  
Current Voltage Relation

Abrupt exposure of 90- to 130-micron diameter chick embryonic myocardial cell aggregates to 10 mM caffeine has been shown to induce a transient inward current. In the present study, we recorded a similar current in small cell clusters (less than 10 cells) in which access of caffeine to each of the cells was rapid. The resulting inward current consisted of a single peak, which decayed exponentially (predominant time constant 335 +/- 130 ms at -40 mV) and had a peak amplitude of up to 15.5 microA/cm2. The caffeine-induced current persisted when the slow inward current was abolished by a 30-s pretreatment with 2 microM D 600 and could be observed at potentials where the fast sodium channels were fully inactivated. The current-voltage relation of the caffeine response was linear between -110 and -40 mV, giving an extrapolated voltage intercept of +12 mV. However, the inward current did not diminish or reverse with further depolarization. A substantial inward current occurred at potentials up to +60 mV, which is more positive than the reversal potential of the tetrodotoxin-sensitive inward current. We conclude that the caffeine-induced current is mediated in part by electrogenic Na+-Ca2+ exchange.

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