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.

Apamin, a highly potent fetal L-type Ca2+ current blocker in single heart cells

1992 ◽  
Vol 262 (2) ◽  
pp. H463-H471 ◽  
Author(s):  
G. Bkaily ◽  
A. Sculptoreanu ◽  
D. Jacques ◽  
D. Economos ◽  
D. Menard
Keyword(s):  
Cell Voltage ◽  
Slow Inward Current ◽  
Heart Cell ◽  
Heart Cells ◽  
Dependent Manner ◽  
Embryonic Chick ◽  
Ventricular Cells ◽  
Chick Heart ◽  
Embryonic Chick Heart

Apamin, a bee venom polypeptide, was reported to block the naturally occurring Ca2+ slow action potentials (APs) in cultured cell reaggregates from old chick hearts [Bkaily, G. et al. Am. J. Physiol. 248 (Heart Circ. Physiol. 17): H961-H965, 1985] as well as the tetrodotoxin (TTX)- and Mn(2+)-insensitive slow Na+ current in young embryonic chick heart cells (Bkaily, G. In Vitro Toxicology. Academic, In press; Bkaily et al. J. Mol. Cell. Cardiol. 23: 25-39, 1991). With the use of the whole cell voltage-clamp technique in single ventricular cells from 10-day-old chick embryos and 17- to 20-wk-old human fetuses, two types of Ca2+ currents (ICa), T and L, were found. These two types of slow inward current in both heart preparations were nearly similar in their voltage, kinetics, and pharmacology. Apamin, a slow Ca2+ action potential blocker in old embryonic chick heart, was found to block the L-type ICa (IL) in a dose-dependent manner without affecting the T-type ICa in both heart cell preparations. The blockade of the IL by apamin was completely reversible upon washout with apamin-free solution. Therefore, when compared with nifedipine or to PN 200-110, apamin seems to be a highly potent L-type Ca2+ channel blocker in heart cells.

scholarly journals Co-culture of embryonic chick heart cells and ciliary ganglia induces parasympathetic responsiveness in embryonic chick heart cells

1993 ◽  
Vol 292 (2) ◽  
pp. 395-399 ◽  
Author(s):  
J V Barnett ◽  
M Taniuchi ◽  
M B Yang ◽  
J B Galper
Keyword(s):  
G Proteins ◽  
Fold Increase ◽  
Heart Cell ◽  
Heart Cells ◽  
Embryonic Chick ◽  
In Ovo ◽  
Chronotropic Response ◽  
Muscarinic Stimulation ◽  
Chick Heart ◽  
Embryonic Chick Heart

We have developed a system for the co-culture of embryonic chick heart cells obtained from embryos at 3.5 days in ovo with ciliary ganglia from chick embryos at 7 days in vivo. After 3 days of co-culture, removal of the ciliary ganglia resulted in complete degeneration of axons within 6-8 h, leaving the post-innervated heart cell culture devoid of neurons. Embryonic chick heart cells at 3.5 days in ovo are unresponsive to muscarinic stimulation. However, following 3 days of co-culture with ciliary ganglia, the heart cells developed a negative chronotropic response to muscarinic stimulation (paired t test, P < 0.02) which persisted for at least 24 h after removal of the ciliary ganglion. The development of muscarinic responsiveness was associated with an increase in the levels of specific alpha-subunits of the guanine nucleotide binding proteins (G-proteins), with a 3-fold increase in the level of alpha 39 (39 kDa subunit) and a 2.5-fold increase in the level of alpha 41. The level of the G-protein subunit alpha s remained unchanged. Culture of embryonic chick heart cells at 3.5 days in ovo with medium conditioned by the growth of embryonic chick heart cells and ciliary ganglia had an effect on the chronotropic response to muscarinic stimulation and on alpha 39 and alpha 41 levels identical to that of co-culture. These data suggest that a soluble factor released during the co-culture of embryonic chick heart cells and ciliary ganglia is capable of inducing muscarinic responsiveness. These studies suggest that innervation of the heart may induce parasympathetic responsiveness by increasing the availability of G-proteins which couple the muscarinic receptor to a physiological response.

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.

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.

Insulin stimulation of protein synthesis in cultured skeletal and cardiac muscle cells

1982 ◽  
Vol 243 (1) ◽  
pp. C81-C86 ◽  
Author(s):  
J. Airhart ◽  
J. A. Arnold ◽  
W. S. Stirewalt ◽  
R. B. Low
Keyword(s):  
Protein Synthesis ◽  
Specific Activity ◽  
Muscle Cells ◽  
Cell Types ◽  
Cardiac Cells ◽  
Cardiac Muscle Cells ◽  
Significant Stimulation ◽  
Chick Heart ◽  
Embryonic Chick Heart ◽  
Stimulation Of

The effects of acute exposure to insulin on protein synthesis were examined in primary, differentiated cultures of embryonic chick heart and skeletal muscle cells. Synthetic rates were calculated using the specific activity of tRNA-bound leucine as precursor, a specific activity that was significantly less than that of extracellular leucine but greater than that of free, intracellular leucine at 0.2 mM external leucine. Insulin did not alter these relationships. Doses of insulin in the physiological range produced significant stimulation of protein synthesis in both cell types. Maximal responses, involving approximately 30% increases in both absolute and fractional rates, were observed at higher insulin concentrations. Significant stimulation by insulin was seen in cardiac cells after only 1 h of insulin treatment, and the effects of the hormone were observed both in the presence and absence of serum in the culture medium.

Hyperaggregability Of Platelets In Cancer, Especially In Reference To Genesis Of DIC

1981 ◽  
Author(s):  
H Yamazaki ◽  
Y Yahara ◽  
T Motomiya ◽  
K Tanoue ◽  
I Isohisa ◽  
...  
Keyword(s):  
Cancer Patients ◽  
Time Course ◽  
Mean Value ◽  
Activated Partial Thromboplastin Time ◽  
Healthy Controls ◽  
Triggering Mechanism ◽  
Coagulation Abnormalities ◽  
Activated Platelets ◽  
The Mean

To clarify the role of platelets in the genesis of DIC in cancer, platelets of cancer patients with and without DIC were examined. Patients studied were 29 cases with cancer in stomach, 17 in lung, 7 in pancreas, 6 in liver (hepatoma), 6 in throat, nose and jaw, 2 in the gall bladder and bilary duct, 2 in uterus and 1 each in the small bowel, rectum and prostate, and 1 each with osteosarcoma, mesothelioma and chorionepithelioma. All patients were in stage 3 or 4. 105 healthy controls were also studied. They were evaluated on a scale of coagulation abnormalities, one point was given for each of the following criteria full-filled, and the score (0 to 4) was used. 1. Platelet count<150xl03Anl. 2. Prothrombin time prolonged more than 1 sec over control and/or activated partial thromboplastin time prolonged more than 10 sec over control. 3. Fibrinogen<250 mg/dl (mean fibrinogen value of the cancer patients minus 1 SD). 4. FDP>20 µg/ml. The patients were distributed with 27 % for score 0, 38 % for 1, 20 % for 2, 7 % for 3 and 8 % for 4. Degrees of abnormality in groups with scores of 3 and 4 were significant when compared to scores 0 and 1, but score 2 was not clearly distinguishable. Platelet mode volume in score 4 was smaller than the other groups. Platelet aggregation by adrenaline and ADP decreased in score 3 and 4, while it increased significantly in score 0 and 1 respectively (P<0.01 -0.05). The mean value of plasma β-TG in the cancer patients as a whole (44±24 ng/ml) was significantly higher than that of control (22±13 ng/ml)(P<0.01). PF4 showed the same tendency. During the time course of the disease, hyperaggrega- bility of platelets associated with increases in β-TG and PF4 was observed before an appearance of DIC syndrome in several cases. The results suggest the existence of hyperfunction of platelets in cancer patients and the possibility of triggering mechanism of such activated platelets in the genesis of DIC in cancer.

Sign in / Sign up

Export Citation Format

Share Document