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G Vassort

Publications and source records attributed to G Vassort.

At least 37 records · Page 2Linked to original sources
PubMed1999

Ionic basis of ventricular arrhythmias in remodeled rat heart during long-term myocardial infarction.

OBJECTIVE: Deleterious electrical abnormalities evolve during myocardial infarction. The goal of this study was to analyse current changes during the late decompensated phase of heart disease induced by coronary ligation and to compare them in various heart regions. METHODS: Young rats were submitted to left coronary ligature. After 4-6 months, cells were enzymatically dissociated and isolated from the upper part basal region of the left ventricle, as well as from the septum, apex and the right ventricle before being studied under whole-cell patch-clamp. RESULTS: Basal L-type Ca2+ current, ICaL elicited at +10 mV did not exhibit regional dependence neither in control nor after post-myocardial infarction (PMI). ICaL showed both a significantly reduced peak amplitude (17.1 +/- 2.8 pA/pF versus 9.9 +/- 1.4 pA/pF in seven control and seven PMI hearts, n = 32 and 40, respectively) and a slower inactivation, such that the amount of inward charges during a 200 ms-depolarizing pulse was nearly unchanged. beta-Adrenergic stimulation was less effective in increasing ICaL in PMI cells but it slowed inactivation further. Significant differences in the K+ currents were observed. A regional distribution was seen for Ito only, with the largest amplitude in the right ventricle (in pA/pF: 23.1 +/- 2.4, 18.2 +/- 3.9, 14.8 +/- 2.4, 8.3 +/- 1.7 in the right ventricle, apex, septum and left ventricle, respectively n = 8, 7, 8 and 9). This was also true in failing heart cells despite Ito being halved in each of the four regions (in pA/pF: 12.2 +/- 2.5, 11.2 +/- 1.9, 5.1 +/- 1.0 and 4.8 +/- 1.0, respectively n = 12, 12, 11 and 13). IK1 was also significantly reduced by 20% in the PMI cells. Two-way analyses of variance demonstrated the absence of interaction between the topographical origin of the cells and the physiological state of the rats. The alpha 1-adrenergic agonist, methoxamine significantly reduced Ito and IK1 to the same extent in both sham and PMI cells, by about 35% and 20% respectively. CONCLUSIONS: Long-term left coronary occlusion induces significant alterations in both Ca2+ and K+ currents that occur with similar amplitude in both ventricles. They include a marked reduction in Ito amplitude as well as a slowing of ICaL inactivation. Both factors could contribute to the disturbances in cellular electrical behaviour and the occurrence of arrhythmias in the post-myocardial infarcted heart.

Action Potentials↗
PubMed1999

A spliced variant of AE1 gene encodes a truncated form of Band 3 in heart: the predominant anion exchanger in ventricular myocytes.

The anion exchangers (AE) are encoded by a multigenic family that comprises at least three genes, AE1, AE2 and AE3, and numerous splicoforms. Besides regulating intracellular pH (pHi) via the Cl-/HCO3- exchange, the AEs exert various cellular functions including generation of a senescent antigen, anchorage of the cytoskeleton to the membrane and regulation of metabolism. Most cells express several AE isoforms. Despite the key role of this family of proteins, little is known about the function of specific AE isoforms in any tissue, including the heart. We therefore chose isolated cardiac cells, in which a tight control of pHi is mandatory for the excitation-contraction coupling process, to thoroughly investigate the expression of the AE genes at both the mRNA and protein levels. RT-PCR revealed the presence of AE1, AE2 and AE3 mRNAs in both neonatal and adult rat cardiomyocytes. AE1 is expressed both as the erythroid form (Band 3 or eAE1) and a novel alternate transcript (nAE1), which was more specifically characterized using a PCR mapping strategy. Two variants of AE2 (AE2a and AE2c) were found at the mRNA level. Cardiac as well as brain AE3 mRNAs were expressed in both neonatal and adult rat cardiomyocytes. Several AE protein isoforms were found, including a truncated form of AE1 and two AE3s, but there was no evidence of AE2 protein in adult rat cardiomyocytes. In cardiomyocytes transfected with an AE3 oligodeoxynucleotide antisense, AE3 immunoreactivity was dramatically decreased but the activity of the Cl-/HCO3- exchange was unchanged. In contrast, intracellular microinjection of blocking anti-AE1 antibodies inhibited the AE activity. Altogether, our findings suggest that a specific and novel AE1 splicoform (nAE1) mediates the cardiac Cl-/HCO3- exchange. The multiple gene and protein expression within the same cell type suggest numerous functions for this protein family.

Age Factors↗
PubMed1998

Extracellular K+ dependence of inward rectification kinetics in human left ventricular cardiomyocytes.

BACKGROUND: In human ventricular cells, the inwardly rectifying K+ current (IK1) is very similar to that of other mammalian species, but detailed knowledge about the K+-dependent distribution of open and blocked states during rectification and about the K+-dependent modulation of inactivation on hyperpolarization is currently lacking. METHODS AND RESULTS: We used the whole-cell patch-clamp technique to record IK1 in myocytes isolated from subendocardial layers of left ventricular septum from patients with nonfailing hearts with aortic stenosis and cardiac hypertrophy who were undergoing open-heart surgery. Outward currents were very small at voltages positive to the reversal potential but increased at high external [K+]. Chord conductance measurements and kinetic analyses allowed us to estimate the proportion of channels in the open state and of those showing either slow unblock or instantaneous unblock (the so-called slow or instantaneous "activation") on hyperpolarization: the distribution in the individual states was dependent on external [K+]. The proportion of channels unblocking slowly was greater than that of channels unblocking instantaneously on hyperpolarization from the plateau voltage range. Hence, because of the previously reported link between the presence of highly protonated blocking molecules and slow unblock kinetics, it is suggested that high cellular concentrations of spermine may account for the low outward current density recorded in these cells. The current decrease observed on extended hyperpolarization was significantly relieved by an increase in external [K+]. CONCLUSIONS: The pattern of IK1 current alterations observed in the present model of human ventricular hypertrophy might favor enhanced excitability and underlie ventricular arrhythmias, possibly via increased intracellular polyamine levels.

Action Potentials↗
PubMed1998

Characteristics of Ca2+ channel blockade by oxodipine and elgodipine in rat cardiomyocytes.

The two novel dihydropyridines, oxodipine and elgodipine greatly depressed the KCl-induced contraction of rabbit aorta and decreased the cardiac force of contraction of rat ventricular strips with lower potency. Both compounds markedly shortened cardiac action potentials. In rat cultured neonatal ventricular myocytes, oxodipine and elgodipine decreased the L-type Ca2+ current (I(CaL)) with IC50 of 0.24 and 0.33 microM respectively while oxodipine was slightly more potent on the T-type Ca2+ current (I(CaT)) than elgodipine (IC50 = 0.41 vs. 2.18 microM). Both compounds were less potent in inhibiting I(CaL) of adult cardiomyocytes. Oxodipine exhibited mostly a tonic block of both currents while elgodipine induced mainly a use-dependent block. Oxodipine and elgodipine increased by at least one order of magnitude their inhibitory potency on I(CaT) and I(CaL) when the cells were partially depolarized. We conclude that the mechanisms of inhibition of Ca2+ channels by these two dihydropyridines are different and suggest that the underlying mechanism of vascular selectivity is the voltage-dependent block of I(CaL), with the use-dependent inhibition of Ca2+ currents by elgodipine further contributing to this selectivity.

Action Potentials↗
PubMed1998

Specific activation of adenylyl cyclase V by a purinergic agonist.

The present study was designed to investigate whether and how the purinergic stimulation of rat ventricular myocytes modulates the cAMP-dependent pathway. Stimulation of cardiomyocytes with ATPgammaS in the presence of the phosphodiesterase inhibitor IBMX increases by 3-fold intracellular cAMP content. In contrast to beta-adrenergic stimulation, the purinergic stimulation of adenylyl cyclase was not inhibited by activation or enhanced by inhibition of a Gi protein. Forskolin did not potentiate the effect of extracellular ATPgammaS on intracellular cAMP content but the effect of isoproterenol did. Like isoproterenol, the purinergic agonist decreased subsequent ADP-ribosylation of a 45 kDa G(alpha s) by cholera toxin. ATPgammaS also increased cAMP content in neonatal rat cardiomyocytes, a cell type that expresses a long form of Gs protein (alpha(s), 52 kDa) in contrast to adult rat cardiomyocytes that express mostly a short form of Gs protein (alpha(s), 45 kDa). Both purinergic and beta-adrenergic agonists increased cAMP in HEK 293 cells expressing type V adenylyl cyclase while cAMP was only increased by beta-adrenergic stimulation of HEK expressing type IV or VI adenylyl cyclases. Thus, we propose that the purinergic and beta-adrenergic stimulations differentially activate adenylyl cyclase isoforms in rat cardiomyocytes and that adenylyl cyclase V is the specific target of the purinergic stimulation.

Adenosine Triphosphate↗
PubMed1998

Src family tyrosine kinase regulates intracellular pH in cardiomyocytes.

The Anion Cl-/HCO3- Exchangers AE1, AE2, and AE3 are membrane pH regulatory ion transporters ubiquitously expressed in vertebrate tissues. Besides relieving intracellular alkaline and CO2 loads, the AEs have an important function during development and cell death and play a central role in such cellular properties as cell shape, metabolism, and contractility. The activity of AE(s) are regulated by neurohormones. However, little is known as to the intracellular signal transduction pathways that underlie this modulation. We show here that, in cardiomyocytes that express both AE1 and AE3, the purinergic agonist, ATP, triggers activation of anion exchange. The AE activation is observed in cells in which AE3 expression was blocked but not in cells microinjected with neutralizing anti-AE1 antibodies. ATP induces tyrosine phosphorylation of AE1, activation of the tyrosine kinase Fyn, and association of both Fyn and FAK with AE1. Inhibition of Src family kinases in vivo by genistein, herbimycin A, or ST638 prevents purinergic activation of AE1. Microinjection of either anti-Cst.1 antibody or recombinant CSK, both of which prevent activation of Src family kinase, significantly decreases ATP-induced activation of AE. Microinjection of an anti-FAK antibody as well as expression in cardiomyocytes of Phe397 FAK dominant negative mutant, also prevents purinergic activation of AE. Therefore, tyrosine kinases play a key role in acute regulation of intracellular pH and thus in cell function including excitation-contraction coupling of the myocardium.

Adenosine Triphosphate↗
PubMed1998

Interstitial ATP level and degradation in control and postmyocardial infarcted rats.

With the aim of estimating interstitial levels and the breakdown process of ATP, cardiac microdialysis was performed in the left ventricular wall of in situ control and postinfarcted as well as of isolated, Langendorff-perfused rat hearts. With the use of a bioluminescence technique for dialysate ATP measurement, the baseline interstitial fluid ATP concentration in in situ hearts was estimated to be 38 +/- 8 nM. Regional ischemia induced an early peak increase in interstitial fluid ATP to 373 +/- 73 nM that correlates with the maximal incidence of ventricular arrhythmias. During continuous infusion of individual adenine nucleotides (50 microM ATP, ADP, or AMP), the dialysate samples were analyzed for adenine nucleotides, nucleosides, and bases using HPLC with ultraviolet detection. The patterns of catabolites were consistent with the major pathway of metabolism, that is, sequential dephosphorylation catalyzed by a chain of separate ecto-nucleotidases. In in situ postinfarcted hearts as well as in perfused hearts, a reduced catabolism rate of extracellular adenine nucleotides was observed. In conclusion, in in situ rat hearts, ATP can be released in substantial amounts in the interstitium where it readily undergoes enzymatic degradation. Dephosphorylation occurs sequentially and faster in in situ control hearts than in in situ postinfarcted or in perfused hearts.

Adenosine↗
PubMed1997

Regional alteration of the transient outward current in human left ventricular septum during compensated hypertrophy.

BACKGROUND: A large calcium-insensitive transient outward current (I(to)) has been recorded in atria, left ventricular (LV) free wall, and right ventricular septal subendocardium of the human heart. Recent studies suggested a major contribution of this current to the electrical heterogeneity of the heart. However, no data have been reported on the distribution of I(to) density within the LV septal wall from compensated human LV hypertrophy. METHODS AND RESULTS: Microelectrode and patch-clamp techniques were used to record action potentials and I(to) in myocytes isolated from superficial (<3 mm deep) and deep (3 to 6 mm deep) layers of LV septum from patients with aortic stenosis and compensated LV hypertrophy. Subendocardial specimens were also obtained from undiseased donor hearts. In none of the superficial subendocardial cells from diseased hearts was a macroscopic I(to) recorded (n=42), whereas in cells from the same location from donor hearts, a typical I(to) was clearly present, with a peak density of 5.88+/-0.78 pA/pF at +60 mV (n=4). However, in deep layers from patients with compensated LV hypertrophy, macroscopic I(to) was present, with a peak density of 10.50+/-2.58 pA/pF at +60 mV (n=4). The absence of I(to) in superficial septal cells from hypertrophied hearts was not due to a divalent cation-related shift of the current kinetics. Instead, extracellular Ca2+ removal induced an I(to)-like current, possibly carried by K+ ions, with a peak density of 30.7+/-2.6 pA/pF at +60 mV (n=29). However, its magnitude, kinetics, and pharmacological characteristics did not allow identification of this current as the usual I(to). CONCLUSIONS: Both topography and pathology can be major modulating factors of the regional distribution of I(to) density in human LV septum. Therefore, they may play a prominent role in determining electrical gradients within this region from which the early depolarization vectors start and the left-to-right activation sequence of the interventricular septum proceeds.

Action Potentials↗
PubMed1997

Purinergic facilitation of ATP-sensitive potassium current in rat ventricular myocytes.

1. The effects of different purinergic agonists on the cardiac adenosine 5'-triphosphate (ATP)-sensitive potassium current (IK(ATP)), appearing during dialysis of rat isolated ventricular myocytes with a low-ATP (100 microM) internal solution under whole-cell patch-clamp conditions, were examined in the presence of a P1 purinoceptor antagonist. 2. The extracellular application of ATP in the micromolar range induced, besides known inward currents through cationic and chloride channels, the facilitation of IK(ATP) once IK(ATP) had already been partially activated during the low-ATP dialysis. 3. Analogues of ATP, alpha, beta-methyleneadenosine 5'-triphosphate (alpha, beta meATP), 2-methylthioadenosine triphosphate (2MeSATP), adenosine 5'-O-3-thiotriphosphate (ATP gamma S) similarly facilitated IK(ATP). UTP and ADP were very weak agonists while AMP and adenosine had no detectable effect. 4. The half-maximal stimulating concentration (C50) of alpha, beta meATP, an analogue that did not elicite the interfering inward cationic current was 1.5 microM. Similar apparent C50 (1-2 microM) were observed for ATP and analogues tested with somewhat less maximal effect of ATP gamma S. 5. Suramin, a nonselective P2-purinoceptor antagonist, altered IK(ATP) at the relatively high concentration required to inhibit purinoceptors. Pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), a supposedly predominantly P2x-purinoceptor antagonist, at micromolar concentration inhibited the transient inward current but did not block the facilitation of IK(ATP). 6. Our results demonstrate that ATP and its analogues facilitate IK(ATP) in rat ventricular myocytes by stimulation of non-P1-, non-P2x-purinoceptors.

Adenosine Triphosphate↗
PubMed1997

Tension response of the cardiotonic agent (+)-EMD-57033 at the single cell level.

The effects of the Ca sensitizer (+)-EMD-57033 were tested on single chemically skinned cells isolated from rat ventricle. The present study demonstrates that (+)-EMD-57033 (10 microM) increased maximal force by 20% (at pCa 4.5) and myofilament Ca sensitivity by 0.2 pCa unit. However, the force-length dependency was not affected by the addition of (+)-EMD-57033, since similar Ca-sensitizing effects occurred at different sarcomere lengths. Consequently, the Ca-sensitizing effect of the drug and of the sarcomere length might be additive. Cross-bridge kinetics were also investigated in the presence of the thiadiazinone derivative. (+)-EMD-57033 induced marked increases in the rate of tension redevelopment (ktr) after brief slack release/restretch, particularly at low Ca concentrations. These results suggest that the Ca-sensitizing effects of (+)-EMD-57033 are due, at least in part, to an increased number of attached cross bridges during one cyclo. This observation, together with the increase in peak force, is discussed in relation to the reduction in energy cost induced by such Ca-sensitizing agents.

Animals↗
PubMed1997

Enhancement of the ATP-sensitive K+ current by extracellular ATP in rat ventricular myocytes. Involvement of adenylyl cyclase-induced subsarcolemmal ATP depletion.

ATP-sensitive K+ (KATP) channels are present at high density in membranes of cardiac cells, where they regulate cardiac function during metabolic impairment. The present study analyzes the effects of extracellular ATP (ATPc), a P2-purinergic agonist that can be released under various conditions in the myocardial cell bed, on KATP current (IK-ATP) in rat ventricular myocytes. Under the whole-cell patch-clamp configuration at a physiological level of intracellular ATP, applying ATPc in the micromolar range did not activate IK-ATP. However, dialyzing the cell with a low-ATP (100 mumol/L) pipette solution elicited a slowly, quasilinearly increasing IK-ATP that was markedly enhanced by applying ATPe in the presence of a Purinergic antagonist. The effect was reversible on washing out the agonist. The IK-ATP enhancement was inhibited by cholera toxin treatment of the myocytes, suggesting that a Gs protein was involved to mediate the effect. Experiments on excised patches allowed us to exclude a membrane-delimited G protein-dependent pathway. Rather, the results suggested that ATPe activates the adenylyl cyclase, since its inhibition by 2'-deoxyadenosine 3'-monophosphate and SQ-22536, which respectively interact with the purine and catalytic site of the cyclase, strongly reduced the ATPe-induced IK-ATP enhancement, whereas neither compound affected IK-ATP in inside-out patches. Inhibition of cAMP-dependent protein kinase by protein kinase inhibitor peptide 5-24 did not alter the purinergic effect. The findings suggests that ATPe triggers the activation of adenylyl cyclase, which causes a subsarcolemmal ATP depletion sufficient to enhance IK-ATP as it develops during low-ATP dialysis of rat ventricular myocytes.

Adenine↗
PubMed1996

Purinergic stimulation of rat cardiomyocytes induces tyrosine phosphorylation and membrane association of phospholipase C gamma: a major mechanism for InsP3 generation.

Phospholipase C gamma (PLC gamma) expression and activation by a purinergic agonist were investigated in adult rat cardiomyocytes. PLC gamma is expressed in isolated cardiomyocytes. Stimulation of cells with extracellular ATP induces a rapid increase in membrane-associated PLC gamma immunoreactivity most probably due to redistribution of the lipase from the cytosol to the membrane. The purine triggers a significant phosphorylation on tyrosine residues of a cytosolic pool of PLC gamma with a time course that correlates with that of translocation. Extracellular ATP also increases intracellular Ins(1,4,5)P3 content. All these events (translocation and phosphorylation of PLC gamma, InsP3 formation) are blocked by genistein, a tyrosine kinase inhibitor. The purinergic effect on both PLC gamma translocation and phosphorylation are Ca-sensitive. We thus propose that the purinergic stimulation activates a non-receptor tyrosine kinase that phosphorylates PLC gamma in the presence of an increased Ca level and induces PLC gamma redistribution to the membrane. There, PLC gamma becomes activated leading to the hydrolysis of phosphatidylinositol diphosphate and in turn Ins(1,4,5)P3 formation. This cascade of events may play a significant role in the induction of arrhythmogenesis by purinergic agonists.

Adenosine Triphosphate↗
PubMed1996

Facilitation of T-type calcium current in bullfrog atrial cells: voltage-dependent relief of a G protein inhibitory tone.

1. The properties of the low-threshold calcium current, ICa,T, were investigated in bullfrog isolated atrial cardiomyocytes using the whole-cell, patch-clamp technique under control conditions and during beta-adrenergic stimulation. 2. The intracellular application of GTP gamma S or adenosine-5'-O-3-thiotriphosphate (ATP gamma S), poorly hydrolysable analogues of GTP and ATP, respectively, barely affected ICa,T amplitude in control conditions. beta-Adrenergic stimulation effects were more marked in the presence of ATP gamma S. 3. The intracellular application of GDP beta S and ADP reduced ICa,T amplitude. In cells pretreated with pertussis toxin, ICa,T amplitude was significantly increased. In both conditions, the addition of isoprenaline was without effect. 4. Under both control and beta-adrenergic-stimulated conditions, a conditioning prepulse to +70 mV did not fully inactivate ICa,T; rather ICa,T facilitation often occurred after beta-adrenergic stimulation. 5. In GTP gamma S- and ATP gamma S-dialysed cells, ICa,T facilitation was generally observed after a prepulse; it was larger in the ATP gamma S dialysis. Facilitation was sustained but ended immediately upon cessation of conditioning prepulses. After beta-adrenergic stimulation, facilitation was more marked in GTP gamma S- than in ATP gamma S-dialysed cells. 6. ICa,T facilitation was prevented by the intracellular application of GDP beta S and by pertussis toxin pretreatment. 7. ICa,T facilitation developed markedly in the presence of intracellular cyclic AMP. This effect was prevented by pertussis toxin pretreatment of the cells. 8. It is thus proposed that ICa,T is under a double antagonistic control by both a Gs and a Gi protein. Furthermore, the double-pulse-induced facilitation of ICa,T results from a voltage-dependent relief of the Gi protein inhibitory tone. Such an effect is increased by protein kinase A-dependent phosphorylation, presumably of the Gi protein.

Animals↗
PubMed1996

Oxidative effects of selenite on rat ventricular contractility and Ca movements.

OBJECTIVE: The study aimed at characterizing the effects of selenite, known for its reactivity with thiols, on cardiac contractility and excitation-contraction coupling. METHODS: The inotropic effects of selenite were studied on rat papillary muscles. Freshly isolated rat ventricular myocytes were used to determine the selenite-induced alterations in thiol contents, free Ca2+ levels (in fura-2 loaded cells), Ca2+ currents and contractile properties of skinned cells. RESULTS: Selenite, at concentrations > or = 0.1 mM, affected muscle contractions by inducing a transient positive inotropic effect (up to 120 +/- 3% of control in 1 mM selenite) followed by a gradual decline of developed tension together with an increase in resting tension (respectively to 37 +/- 3 and 166 +/- 5% of their control values after 20 min exposure). These changes, irreversible on washout, could be reversed by the disulfonic reducing agent dithiothreitol (DTT, 1 mM). Lowering temperature from 35 degrees to 22 degrees C or preincubating the muscles with the disulfonic stilbene SITS (0.2 mM) completely prevented the selenite-induced transient positive inotropy and rise in resting tension. In isolated myocytes, 10 min exposure to 1 mM selenite induced a 40 +/- 9% decrease of total sulfhydryl content. At this concentration, selenite rapidly caused a rise of basal [Ca2+]i together with a diminution of the Ca2+ spike amplitude (respectively to 165 +/- 15 and 45 +/- 9% of their control values after 5 min exposure). In addition, selenite significantly enhanced at each Ca2+ concentration the force generated by skinned myocytes. Ca2+ currents, measured at 22 degrees C, decreased by 28 +/- 8% in the presence of 1 mM selenite. These effects were reversed by DTT. CONCLUSIONS: The results demonstrate that selenite, through alterations of cellular thiol redox status, induced a dual action on muscle contraction that can be imputed to a combined action on Ca2+ channels, Ca2+ transporters and contractile proteins. Extracellular negative effects of selenite are due to a partial reduction of Ca2+ current magnitude. Intracellular effects are mediated both by a diminution of Ca2+ handing by intracellular organelles and by a sensitization of the contractile to Ca2+ ions. The results further indicate that selenite uptake into the cardiac cells occurs mainly through the temperature-sensitive anion exchanger.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1996

Ca-dependence of isometric force kinetics in single skinned ventricular cardiomyocytes from rats.

OBJECTIVES: The effects of Ca2+ on the rate of tension redevelopment following a brief release/restretch were investigated in single chemically-skinned ventricular myocytes from the rat. METHODS: The myocytes were enzymatically isolated and skinned using Triton-X100. They were then attached with an optical adhesive glue to glass micropipettes fixed to a piezoelectric translator and a force transducer. Tension redevelopment was measured at various levels of Ca activation after disrupting force-generating crossbridges by a brief (20 ms) step release/restretch equivalent to 20% of the original 2.1 microns sarcomere length. Most of tension redevelopment was well fitted by a monoexponential function. RESULTS: At maximal Ca concentrations, pCa 4.5 maximal force was obtained at 2.1 microns sarcomere length and averaged 11.8 +/- 0.7 microN. The rate of tension redevelopment (ktr) increased with increasing Ca concentrations up to 5.19 +/- 0.37.s-1 at maximal Ca activation. The relation between the rate of tension redevelopment and Ca concentration was sigmoidal and could be fitted by the Hill equation with coefficients similar to those describing the tension-pCa relation. The relation between relative rate of tension redevelopment and relative steady activated tension was curvilinear increasing with increasing Ca concentration. CONCLUSIONS: In cardiac muscle, Ca2+ modulates both the number and the kinetics of force-generating crossbridges in a manner similar to that previously reported in skeletal muscle.

Animals↗
PubMed1995

Identification of band 3-like proteins and Cl-/HCO3- exchange in isolated cardiomyocytes.

The identification of the protein that exerts the function of Cl-/HCO3- exchange is still unresolved in cardiac tissue. We have addressed this issue by using a multiple technical approach. Western blotting analysis with an antibody raised against human erythroid whole band 3 protein, the so-called protein that mediates the Cl-/HCO3- exchange in erythrocytes, showed that adult cardiomyocytes expressed two proteins immunologically related to the erythroid band 3. These proteins migrated in SDS-polyacrylamide gel electrophoresis with apparent molecular masses of 80 and 120 kDa. They were specifically found in the membrane but not in the cytosolic or the myofibril fractions of adult cardiomyocytes. Confocal microscopy further indicated that the immunostained proteins were mainly located at the sarcolemma and along T-tubules, typical membrane structures of adult cardiomyocytes. Using an antibody raised against a cardiac amino-terminal domain of rat AE3, we found that the 120-kDa protein is the translation product of the AE3 gene specifically expressed in heart and brain. Using an antiserum raised against a specific domain of mouse erythroid band 3 (AE1), which is not shared by AE3, we showed that the 80-kDa protein is likely to be a truncated translation product of the AE1 gene. Microinjection of the anti-human erythroid whole band 3 antibody into single isolated cardiac cells significantly inhibited the Cl-/HCO3- exchange activity. Furthermore, the anti-AE1 antibody strongly decreased the efficiency of 4,4'-diisothiocyanatostilbene-2,2'-disulfonate to inhibit the ionic exchange. We thus suggest that the 80-kDa or both the 80- and the 120-kDa proteins immunologically related to the erythroid band 3 protein perform the anionic exchange in rat cardiomyocytes.

Amino Acid Sequence↗
PubMed1995

Aldosterone modulates both the Na/H antiport and Cl/HCO3 exchanger in cultured neonatal rat cardiac cells.

Mineralocorticoid hormones regulate many physiological functions in the cardiovascular system. Although high affinity binding sites for aldosterone have been found in myocardium, aldosterone effects on pHi regulatory systems in cardiac cells have not been described. We have addressed this issue by using microspectrofluorimetric monitoring of intracellular pH in developing neonatal rat cardiomyocytes cultured for 2 weeks. Developmental changes in cell morphology were controlled by anti-myosin light chain antibody staining of the sarcomeric units using confocal laser scanning microscopy. The data obtained demonstrate that from early stages of the development, pHi in neonatal cardiac cells is regulated by three ion transporting mechanisms, namely, Na/H antiport, Na- and HCO3-dependent transporter and Cl/HCO3 exchanger. A 24-h treatment of the cells with aldosterone increases the activity of the Cl/HCO3 exchanger at day 6 of cell culture while the Na/H antiport activity is enhanced in the cells treated with the hormone at days 9 and 13 of culture. Thus, by affecting the activity of ionic transporters, aldosterone modulates acid-base balance in cardiac cells.

Aldosterone↗