scholarly journals The initial inward current in spherical clusters of chick embryonic heart cells.

1980 ◽  
Vol 75 (4) ◽  
pp. 437-456 ◽  
Author(s):  
L Ebihara ◽  
N Shigeto ◽  
M Lieberman ◽  
E A Johnson
Keyword(s):  
Time Constant ◽  
Time Course ◽  
Sodium Current ◽  
Reversal Potential ◽  
Giant Axon ◽  
Heart Cells ◽  
Voltage Step ◽  
Inward Current ◽  
Chick Heart ◽  
Embryonic Chick Heart

The rapid inward sodium current in spherical clusters of 11-d-old embryonic chick heart cells, ranging in size between 65 and 90 micron diameter, was studied using the two-microelectrode voltage-clamp technique. Using these preparations, it was possible to resolve the activation phase of the rapid inward current for potentials negative to -25 mV at 37 degrees C. The rapid inward current exhibited a voltage and time dependence similar to that observed in other excitable tissues. It was initiated at potential steps more positive than -45 mV. The magnitude of the current reached its maximum value at a potential of approximately -20 mV. The measured reversal potential was that predicted by the Nernst equation for sodium ions. The falling phase of the current followed a single exponential time-course with a time constant of inactivation, tau h, ranging between 2.14 ms at -40 mV and 0.18 ms at -5 mV. The time constant of inactivation, tau h, determined by a single voltage-step protocol was compared to the constant, tau c, determined by a double voltage-step protocol and no significant different between the two constants of inactivation was found. Furthermore, the time constants of inactivation and reactivation at the same potential in the same preparation were similar. The results of this study demonstrate that the sodium current of heart cells recorded at 37 degrees C can be described by Hodgkin-Huxley kinetics with speeds approximately four times faster than the squid giant axon at 15 degrees C.

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.

scholarly journals Tetrodotoxin Desensitization in Aggregates of Embryonic Chick Heart Cells

1973 ◽  
Vol 62 (3) ◽  
pp. 286-302 ◽  
Author(s):  
Terence F. McDonald ◽  
Howard G. Sachs ◽  
Robert L. DeHaan
Keyword(s):  
Protein Synthesis ◽  
Time Course ◽  
Mean Value ◽  
Slow Inward Current ◽  
Heart Cell ◽  
Heart Cells ◽  
Initial Sensitivity ◽  
Chick Heart ◽  
Embryonic Chick Heart ◽  
The Mean

Spontaneous beating of heart-cell aggregates from 4-day chick embryos was initially blocked by 10-5 g/ml tetrodotoxin (TTX). With continued exposure to the drug, the fraction of blocked aggregates decreased from about 80% at 15 min to about 25% at 2–3 h, at which time, beating aggregates had become desensitized to the toxin, showing no response to a fresh dose. Aggregates from 5-day hearts were more sensitive to TTX, but fewer became desensitized in its presence. Desensitization to TTX was not seen in 6- and 7-day aggregates. Inhibition of protein synthesis by cycloheximide did not affect beating or initial sensitivity to TTX of 4-day aggregates, but desensitization failed to occur. Before TTX, the mean value of maximal upstroke velocity (Vmax) of the action potentials in 4-day aggregates was 33 V/s. After desensitization Vmax was 12 V/s. Activity of desensitized aggregates in the presence of TTX was augmented by elevated calcium levels, and suppressed by presumed inhibitors of slow inward current (manganese, D600). Desensitization was reversible; upon removal of TTX 10-5 g/ml, aggregates regained their responsiveness to a fresh dose of the drug with a 2–3 h time-course similar to that of desensitization. This was prevented by continued exposure to TTX at concentrations as low as 10-8 g/ml. These data suggest that (a) desensitization involves a change in the mode of action-potential generating from one involving Na-specific, TTX-sensitive channels to one utilizing slower Mn-sensitive channels; (b) the process of desensitization occurs over a period of 2–3 h and is dependent upon the products of protein synthesis; and (c) desensitization is reversible after removal of TTX over a 2–3 h time-course similar to its onset.

Development of the fast sodium current in early embryonic chick heart cells

1988 ◽  
Vol 101 (1) ◽  
pp. 209-223 ◽  
Author(s):  
Shiroh Fujii ◽  
Richard K. Ayer ◽  
Robert L. DeHaan
Keyword(s):  
Sodium Current ◽  
Heart Cells ◽  
Embryonic Chick ◽  
Chick Heart ◽  
Embryonic Chick Heart ◽  
Fast Sodium Current

Techniques for cryoultramicrotomy of propane jet frozen biological samples

1986 ◽  
Vol 44 ◽  
pp. 260-261
Author(s):  
B. Craig ◽  
L. Hawkey ◽  
A. LeFurgey
Keyword(s):  
Freeze Fracture ◽  
Freeze Substitution ◽  
Heart Cells ◽  
Crystal Formation ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Chick Heart ◽  
Embryonic Chick Heart ◽  
A New Technique

Ultra-rapid freezing followed by cryoultramicrotomy is essential for the preservation of diffusible elements in situ within cells prior to scanning transmission electron microscopy and quantitative energy dispersive x-ray microanalysis. For cells or tissue fragments in suspension and for monolayer cell cultures, propane jet freezing provides cooling rates greater than 30,000°C/sec with regions up to 40μm in thickness free of significant ice crystal formation. While this method of freezing has frequently been applied prior to freeze fracture or freeze substitution, it has not been widely utilized prior to cryoultramicrotomy and subsequent x-ray microanalytical studies. This report describes methods devised in our laboratory for cryosectioning of propane jet frozen kidney proximal tubule suspensions and cultured embryonic chick heart cells, in particular a new technique for mounting frozen suspension specimens for sectioning. The techniques utilize the same specimen supports and sample holders as those used for freeze fracture and freeze substitution and should be generally applicable to any cell suspension or culture preparation.

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