scholarly journals Photoinduced removal of nifedipine reveals mechanisms of calcium antagonist action on single heart cells.

1985 ◽  
Vol 86 (3) ◽  
pp. 353-379 ◽  
Author(s):  
A M Gurney ◽  
J M Nerbonne ◽  
H A Lester
Keyword(s):  
Calcium Channels ◽  
Dissociation Constants ◽  
Light Flash ◽  
Cardiac Cells ◽  
Current Amplitude ◽  
Neonatal Rat ◽  
Resting Potential ◽  
Open Channels ◽  
Heart Cell ◽  
Heart Cells

The currents through voltage-activated calcium channels in heart cell membranes are suppressed by dihydropyridine calcium antagonists such as nifedipine. Nifedipine is photolabile, and the reduction of current amplitude by this drug can be reversed within a few milliseconds after a 1-ms light flash. The blockade by nifedipine and its removal by flashes were studied in isolated myocytes from neonatal rat heart using the whole-cell clamp method. The results suggest that nifedipine interacts with closed, open, and inactivated calcium channels. It is likely that at the normal resting potential of cardiac cells, the suppression of current amplitude arises because nifedipine binds to and stabilizes channels in the resting, closed state. Inhibition is enhanced at depolarized membrane potentials, where interaction with inactivated channels may also become important. Additional block of open channels is suggested when currents are carried by Ba2+ but is not indicated with Ca2+ currents. Numerical simulations reproduce the experimental observations with molecular dissociation constants on the order of 10(-7) M for closed and open channels and 10(-8) M for inactivated channels.

Engineered Membranes Improve Cardiac Function in Ischemic Rat Hearts

2010 ◽  
Author(s):  
Monica Sandri ◽  
Anna Tampieri ◽  
Joung H. Levialdi Ghiron ◽  
Gianluigi Condorelli
Keyword(s):  
Cardiac Function ◽  
Cardiac Tissue ◽  
Diglycidyl Ether ◽  
Beating Heart ◽  
Cardiac Cells ◽  
Neonatal Rat ◽  
Heart Cell ◽  
Collagen Membrane ◽  
Heart Cells ◽  
Type I

In the relatively young field of cardiac tissue engineering, different biomaterials, methods and techniques have been tested for cardiac repair. In this study we examined the validity of a series of new preformed membrane scaffolds, based on collagen type I, for the transplantation of cardiac cells. One type of membrane, cross-linked with 1,4-butanediol diglycidyl ether (BDDGE) and fibronectin-enriched, gave rise to spontaneously beating heart cell constructs 5–9 days after seeding with neonatal rat cardiac cells. This membrane was then grafted, with and without beating cardiac cells, onto the infarcted area of rat models of heart failure. Seriate echocardiography, performed on rats before transplantation and at 4 and 8 weeks after transplantation, showed that rats that received collagen membranes with beating cells showed an improvement in cardiac function after 8 weeks. These results suggest that this new type of collagen membrane can be used as vector for the transplantation of beating heart cells to the injured myocardium, hence representing an important potential tool for cardiac tissue repair technologies.

Confocal imaging of calcium in intact ventricular muscle provides a new view of excitation-contraction coupling

1996 ◽  
Vol 54 ◽  
pp. 738-739
Author(s):  
W.G. Wier
Keyword(s):  
Local Control ◽  
Cardiac Tissue ◽  
Cell Function ◽  
Isolated Heart ◽  
Cardiac Cells ◽  
Confocal Imaging ◽  
Ion Concentration ◽  
Heart Cell ◽  
Free Calcium ◽  
Heart Cells

A fundamentally new understanding of cardiac excitation-contraction (E-C) coupling is being developed from recent experimental work using confocal microscopy of single isolated heart cells. In particular, the transient change in intracellular free calcium ion concentration ([Ca2+]i transient) that activates muscle contraction is now viewed as resulting from the spatial and temporal summation of small (∼ 8 μm3), subcellular, stereotyped ‘local [Ca2+]i-transients' or, as they have been called, ‘calcium sparks'. This new understanding may be called ‘local control of E-C coupling'. The relevance to normal heart cell function of ‘local control, theory and the recent confocal data on spontaneous Ca2+ ‘sparks', and on electrically evoked local [Ca2+]i-transients has been unknown however, because the previous studies were all conducted on slack, internally perfused, single, enzymatically dissociated cardiac cells, at room temperature, usually with Cs+ replacing K+, and often in the presence of Ca2-channel blockers. The present work was undertaken to establish whether or not the concepts derived from these studies are in fact relevant to normal cardiac tissue under physiological conditions, by attempting to record local [Ca2+]i-transients, sparks (and Ca2+ waves) in intact, multi-cellular cardiac tissue.

scholarly journals Ability of the orally effective iron chelators dimethyl- and diethyl- hydroxypyrid-4-one and of deferoxamine to restore sarcolemmal thiolic enzyme activity in iron-loaded heart cells

Blood ◽  
1994 ◽  
Vol 83 (9) ◽  
pp. 2692-2697 ◽  
Author(s):  
G Link ◽  
A Pinson ◽  
C Hershko
Keyword(s):  
Enzyme Activity ◽  
Iron Chelation ◽  
Myocardial Cell ◽  
Resting Potential ◽  
Molar Ratio ◽  
Iron Chelators ◽  
Heart Cell ◽  
Heart Cells ◽  
Cell Organelles ◽  
Rat Heart Cells

In view of the profound functional and structural abnormalities shown in our previous studies in cultured, iron-loaded rat heart cells, we have examined the ability of the orally effective iron chelators dimethyl-3-hydroxypyrid-4-one (DMHP or L1) and diethyl-3-hydroxy-pyrid- 4-one (DEHP or CP94) and of deferoxamine (DF) to reverse the damage caused by iron loading to heart cell organelles. At a concentration of 1.0 mmol/L, all three iron chelators were equally efficient in removing iron and restoring the activity of the thiolic sarcolemmal enzymes 5′- nucleotidase and Na,K,ATPase. However, at 0.1 mmol/L DMHP and DEHP were less effective than DF both in their iron-mobilizing effect and in promoting thiolic enzyme recovery. The superior efficiency of DF at low concentrations illustrates the advantage of the hexadentate chelating action of DF as compared with bidentate chelators such as DMHP and DEHP requiring a 3 to 1 molar ratio to iron for optimal effect. In contrast to its beneficial effect on sarcolemmal enzyme activity, iron chelation was unable to reverse the increase in beta-hexosaminidase activity caused by abnormal lysosomal fragility. Our study demonstrates for the first time that iron-induced peroxidative damage to the myocardial cell is associated with a marked loss of Na,K,ATPase activity, an enzyme with a major role in the maintenance of cellular resting potential. The timing of this damage and the restoration of Na,K,ATPase function by iron-chelating treatment suggest a cause-and-effect relationship between the observed injury to the sarcolemmal enzyme and the reversible electrophysiologic abnormalities observed in the same heart culture system in our previous studies.

Diffusion and electrogenic components of the resting potential in explanted neonatal rat ventricle cells

1987 ◽  
Vol 65 (10) ◽  
pp. 2110-2116
Author(s):  
Martine LeFloch ◽  
Otto F. Schanne ◽  
Elena Ruiz-Ceretti
Keyword(s):  
Cardiac Cells ◽  
Neonatal Rat ◽  
Resting Potential ◽  
Channel Blockers ◽  
Ca Channel ◽  
High K ◽  
The Mean ◽  
The Difference ◽  
Rat Ventricle ◽  
Steady Potential

Spontaneously beating explanted neonatal rat ventricle cells stop beating and show a steady potential (the mean resting potential, −46.2 mV at 6.0 mM Ko) when exposed to 10 mM Cao or 4 mM Mn. When Ko was increased, resting potential changed only slightly between 3 and 15 mM, but the resting potential versus Ko characteristically approached the slope of a K electrode at high Ko Elimination of Cl from the medium did not alter the K dependence of the resting potential. However, a hyperpolarization of 9 mV per 10-fold change was observed when Nao was decreased from 50 to 4 mM. Ouabain (10−4 M) depolarized the membrane within 2 min to a stable level of about −30 mV in spontaneously beating cells and in those treated with Ca channel blockers. This potential was considered as the diffusion component of the membrane potential, Vdiff. Consequently the difference between resting potential and Vdiff represents the ouabain-sensitive or the electrogenic component of the resting potential. Using linearized versions of the Mullins and Noda as well as the Goldman – Hodgkin – Katz equations, we calculated that a PNa/PK between 0.25 and 0.35, a Na/K exchange ratio of 2.0, and a Ki of 160 mM adequately described the K dependence of the resting potential. We demonstrated the contribution of electrogenic Na extrusion to the resting potential of mammalian cardiac cells in culture. Therefore the existence of a composite resting potential precludes the direct comparison of potential measurements obtained under conditions liable to independently modify either the diffusion or the electrogenic component.

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.

scholarly journals Adenosine formation and release from neonatal-rat heart cells in culture

1985 ◽  
Vol 229 (3) ◽  
pp. 799-805 ◽  
Author(s):  
P Meghji ◽  
C A Holmquist ◽  
A C Newby
Keyword(s):  
Rat Heart ◽  
Neonatal Rat ◽  
Heart Cell ◽  
Heart Cells ◽  
Dependent Manner ◽  
Nucleoside Transporter ◽  
Concentration Dependent Manner ◽  
Cells In Culture ◽  
Neonatal Rat Heart ◽  
Rat Heart Cells

The incorporation of [3H]adenosine (10 microM) into neonatal-rat heart cell nucleotides was inhibited in a concentration-dependent manner, such that 50% inhibition was obtained with 0.75 microM-dipyridamole, 0.26 microM-hexobendine or 0.22 microM-dilazep. Adenosine formation was accelerated 2.5-fold to 2.1 +/- 0.3 nmol/10(7) cells in 10 min when cells were incubated with a combination of 30 mM-2-deoxyglucose and 2 micrograms of oligomycin/ml. Of the newly formed adenosine, 6 +/- 2% was in the cells. Dipyridamole, hexobendine or dilazep (10 microM) increased the amount of adenosine in the cells and decreased that in the medium such that 45-50% of the newly formed adenosine was in the cells. Antibodies which inhibited ecto-5'-nucleotidase by 98.7 +/- 0.3% did not alter the rate of adenosine formation or its distribution between cells and medium. We conclude that adenosine was formed in the cytoplasm during catabolism of cellular ATP and was released via the dipyridamole-sensitive symmetric nucleoside transporter.

scholarly journals Ability of the orally effective iron chelators dimethyl- and diethyl- hydroxypyrid-4-one and of deferoxamine to restore sarcolemmal thiolic enzyme activity in iron-loaded heart cells

Blood ◽  
1994 ◽  
Vol 83 (9) ◽  
pp. 2692-2697 ◽  
Author(s):  
G Link ◽  
A Pinson ◽  
C Hershko
Keyword(s):  
Enzyme Activity ◽  
Iron Chelation ◽  
Myocardial Cell ◽  
Resting Potential ◽  
Molar Ratio ◽  
Iron Chelators ◽  
Heart Cell ◽  
Heart Cells ◽  
Cell Organelles ◽  
Rat Heart Cells

Abstract In view of the profound functional and structural abnormalities shown in our previous studies in cultured, iron-loaded rat heart cells, we have examined the ability of the orally effective iron chelators dimethyl-3-hydroxypyrid-4-one (DMHP or L1) and diethyl-3-hydroxy-pyrid- 4-one (DEHP or CP94) and of deferoxamine (DF) to reverse the damage caused by iron loading to heart cell organelles. At a concentration of 1.0 mmol/L, all three iron chelators were equally efficient in removing iron and restoring the activity of the thiolic sarcolemmal enzymes 5′- nucleotidase and Na,K,ATPase. However, at 0.1 mmol/L DMHP and DEHP were less effective than DF both in their iron-mobilizing effect and in promoting thiolic enzyme recovery. The superior efficiency of DF at low concentrations illustrates the advantage of the hexadentate chelating action of DF as compared with bidentate chelators such as DMHP and DEHP requiring a 3 to 1 molar ratio to iron for optimal effect. In contrast to its beneficial effect on sarcolemmal enzyme activity, iron chelation was unable to reverse the increase in beta-hexosaminidase activity caused by abnormal lysosomal fragility. Our study demonstrates for the first time that iron-induced peroxidative damage to the myocardial cell is associated with a marked loss of Na,K,ATPase activity, an enzyme with a major role in the maintenance of cellular resting potential. The timing of this damage and the restoration of Na,K,ATPase function by iron-chelating treatment suggest a cause-and-effect relationship between the observed injury to the sarcolemmal enzyme and the reversible electrophysiologic abnormalities observed in the same heart culture system in our previous studies.

Localization of the Na/Ca exchange-dependent Ca compartment in cultured neonatal rat heart cells

1995 ◽  
Vol 268 (1) ◽  
pp. C119-C126 ◽  
Author(s):  
G. A. Langer ◽  
S. Y. Wang ◽  
T. L. Rich
Keyword(s):  
Total Content ◽  
Cardiac Cells ◽  
Neonatal Rat ◽  
High Dose ◽  
Heart Cells ◽  
Cell Content ◽  
Intact Cells ◽  
Content Ratio ◽  
On Line ◽  
Rat Heart Cells

It has been previously established, in both adult and cultured neonatal cardiac cells, that there is a discrete Na/Ca exchange-dependent Ca compartment. It has been proposed that a component of junctional sarcoplasmic reticulum (JSR) Ca and Ca bound to the apposed inner sarcolemmal leaflet represent together the subcellular locus of the compartment. The present study examines this proposal. The amount of Ca in the total compartment is measured isotopically in intact functional cells (using the on-line "scintillation disk" technique) under a variety of perfusion conditions. Under identical labeling conditions, sarcolemmal membranes are rapidly (within a few hundred milliseconds) isolated from another set of intact cells by "gas dissection," and the amount of Ca bound to the membranes is measured. Probes that specifically decrease SR Ca content (thapsigargin, caffeine, low-dose ryanodine) decrease total cell content and sarcolemmal binding proportionally. High-dose ryanodine (producing closure of SR channels) markedly reduces sarcolemmal binding relative to total content of the compartment. The sarcolemmal sites saturate between 1 and 2 mM extracellular Ca ([Ca]o), whereas the total compartment saturates between 4 and 6 mM [Ca]o. Below 1 mM [Ca]o, sarcolemmal binding is maintained relative to total compartment content. Finally, the total compartment increases after reversal of the intracellular Na to extracellular Na ([Na]i/[Na]o) gradient with sarcolemmal content-to-total content ratio dependent on the method used to reverse the [Na]i/[Na]o ratio. The results are consistent with localization of the Na/Ca exchange-dependent compartment to the subsarcolemmal region ("cleft") where JSR Ca is in equilibrium with anionic inner sarcolemmal leaflet Ca binding sites.

scholarly journals Preferential distribution of non-esterified fatty acids to phosphatidylcholine in the neonatal mammalian myocardium

1984 ◽  
Vol 224 (2) ◽  
pp. 651-659 ◽  
Author(s):  
N A Schroedl ◽  
C R Hartzell
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Early Period ◽  
Neonatal Rat ◽  
Nonesterified Fatty Acid ◽  
Heart Cell ◽  
Heart Cells ◽  
Nonesterified Fatty Acids ◽  
Mammalian Heart ◽  
Esterified Fatty Acids

Non-esterified fatty acids are used to a limited extent as an energy source in the newborn-mammalian heart. Therefore additional roles for palmitic and oleic acids during this early period of growth and development were investigated in the cultured neonatal-rat heart cell model system. Our results indicate significant differences in nonesterified-fatty-acid metabolism exist in this system in comparison with the adult rat or embryonic chick heart. Initial rates of depletion of palmitate and oleate from serum-free growth medium by heart cells obtained from 2-day-old rats and maintained in culture for 10 or 11 days were 111 +/- 2 and 115 +/- 3 pmol/min per mg of protein respectively. In serum-containing medium, the initial depletion rates were 103 +/- 3 and 122 +/- 4 pmol/min per mg of protein respectively, when endogenous serum nonesterified-fatty-acid concentrations were included in rate calculations. Less than 1% of the intracellularly incorporated fatty acids were found in aqueous products at any time. After 25 h, 15.5% of the initial palmitate was deposited intracellularly in the phosphatidylcholine lipid fraction, 4.2% in the triacylglycerol + fatty-acid-ester fraction and 3.1% in the sphingomyelin fraction. These results contradict the classical view, based on findings with the lipid-dependent adult heart, that exogenous nonesterified fatty acids are directed intracellularly primarily to pathways of oxidation or to storage as triacylglycerol. More importantly, it underscores the significance of exogenous non-esterified fatty acids in membrane biosynthesis of the developing mammalian heart. Included here is a new method for one-dimensional t.l.c. separation of metabolically important polar lipids.

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