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European Journal of Heart Failure 2002 4(3):249-254; doi:10.1016/S1388-9842(02)00016-8
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© 2002 European Society of Cardiology

Hypertrophic responsiveness of cardiomyocytes to {alpha}- or β-adrenoceptor stimulation requires sodium-proton-exchanger-1 (NHE-1) activation but not cellular alkalization

Matthias Schäfer, Claudia Schäfer, Hans Michael Piper and Klaus-Dieter Schlüter*

Physiologisches Institut Justus-Liebig Universität, Aulweg 129, D-35392 Giessen, Germany

* Corresponding author. Tel.: +49-641-99-47-212; fax: +49-641-99-47-239. E-mail address: klaus-dieter.schlueter{at}physiologie.med.uni-giessen.de


   Abstract
Top
 Abstract
1. Introduction
 2. Materials and methods
 3. Materials
 4. Results
 5. Discussion
 Acknowledgments
 References
 
The influence of the sodium-proton-exchanger-1 (NHE-1) inhibitor HOE694 on {alpha}- or β-adrenoceptor mediated stimulation of protein synthesis was investigated in cultured ventricular cardiomyocytes from adult rat pre-treated with fetal calf serum to induce hypertrophic responsiveness to β-adrenoceptor stimulation. Stimulation of {alpha}-adrenoceptors with phenylephrine (10 µM) in bicarbonate-free medium caused cellular alkalization ({Delta}pHi: +0.17±0.02, n=5, P<0.05). HOE694, an NHE-1 inhibitor, completely abolished this effect. [14C]phenylalanine incorporation into cellular protein mass increased in the presence of phenylephrine by 23±8%, and this effect was also abolished in the presence of HOE694. HOE694 (1 µM) neither influenced basal protein synthesis nor interfered with {alpha}-adrenoceptor mediated activation of ERK2. Phorbol myristate acetate, a direct stimulator of protein kinase C, mimicked the effect of {alpha}-adrenoceptor stimulation in regard to protein synthesis, but did not lead to cellular alkalization. Protein synthesis increased in the presence of isoprenaline, a β-adrenoceptor agonist also. Again, HOE694 attenuated the stimulation of protein synthesis although isoprenaline did not cause cellular alkalization. In conclusion, the growth response to different hypertrophic stimuli, namely {alpha}- or β-adrenoceptor stimulation, is attenuated in the presence of the NHE-1 inhibitor HOE694 and this inhibition is independent from cellular alkalization.

Key Words: Myocardial hypertrophy • Cellular alkalization • Protein kinase C

Received March 1, 2001; Revised September 4, 2001; Accepted December 1, 2001


   1. Introduction
Top
 Abstract
 1. Introduction
2. Materials and methods
 3. Materials
 4. Results
 5. Discussion
 Acknowledgments
 References
 
It has been suggested that neuroendocrine activation plays an important role in the pathogenesis of myocardial hypertrophy and heart failure [1]. Indeed, several hormones and neurohormonal factors are able to induce hypertrophic growth of adult ventricular cardiomyocytes (reviewed in [2]). The intracellular steps involved in the hypertrophic growth response to these factors are only partly characterized. In the case of {alpha}1-adrenoceptor stimulation, an induction of hypertrophic growth depends on the activation of protein kinase C (PKC), followed by an activation of PI3-kinase and p70s6k [3–5]. Activation of PKC by phenylephrine also activates the mitogen activated protein kinase, ERK2, but this activation is not involved in signaling pathways required for an acceleration of protein synthesis (reviewed in [6]). Instead, it leads to the re-expression of fetal type proteins, which represents another characteristic feature for many forms of myocardial hypertrophy.

An involvement of sodium-proton-exchanger-1 (NHE-1) in the intracellular signaling leading to a hypertrophic response has been hypothesized, because an inhibition of NHE-1 by amiloride attenuates the hypertrophic growth response to {alpha}-adrenoceptor stimulation [7]. Activation of NHE-1 by phenylephrine causes cytosolic alkalization [8,9]. This may lead to an increase in creatine phosphate concentration, due to alterations of the creatine kinase equilibrium. In whole hearts and isolated cardiomyocytes a correlation between protein synthesis and creatine phosphate concentration can be observed, suggestive of a causal relationship [10]. Using the NHE-1 inhibitor HOE694 and β-guanidinpropionic acid, we showed recently, however, that this relationship does not exist [9]. Nevertheless, in the presence of HOE694 the growth response of myocardial cells to {alpha}-adrenoceptor stimulation is attenuated. The mechanism by which HOE694 attenuates the increase in protein synthesis and thereby cellular hypertrophy is yet to be identified. It is also an open question whether participation of NHE-1 in the signaling leading to an increase in protein synthesis is part of other hypertrophic stimuli as well.

In this study we used cultured adult cardiomyocytes, which respond to {alpha}- or β-adrenoceptor stimulation with an increase in [14C]phenylalanine incorporation. Isolated cardiomyocytes from adult rats do not normally show a hypertrophic response to β-adrenoceptor stimulation [3,11]. Specific culture conditions, namely low concentrations of isoprenaline [12] or high concentrations of fetal calf serum [13], induce a hypertrophic responsiveness to β-adrenoceptor stimulation. In cases of high concentrations of fetal calf serum, this induction is mediated by autocrine activation with TGF-β1 [14]. The β-adrenoceptor mediated hypertrophic growth effect shows differences in the intracellular signaling compared to {alpha}-adrenoceptor stimulation, e.g. it is cAMP-dependent but PKC-independent [15]. It also shares, however, common signaling elements with the {alpha}-adrenoceptor mediated growth effect, e.g. activation of PI3 kinase and p70s6k [4,5]. The use of this cell culture system allows analysis of the influence of HOE694 on the hypertrophic growth effect of {alpha}- or β-adrenoceptor stimulation.

The precise mechanisms by which HOE694 interferes with the intracellular signaling pathways leading to hypertrophic growth is unknown. We investigated, first, whether cellular alkalization, which may accompany NHE-1 activation plays a causal role in the stimulation of protein synthesis, and second, whether NHE-1 activation is part of the hypertrophic signaling evoked by either of {alpha}- or β-adrenoceptor stimulation.


   2. Materials and methods
Top
 Abstract
 1. Introduction
 2. Materials and methods
3. Materials
 4. Results
 5. Discussion
 Acknowledgments
 References
 
2.1. Cell culture
Ventricular heart muscle cells were isolated from 200–250-g male Wistar rats as previously described [3]. Isolated cells were suspended in FCS-free culture medium and plated at a density of 1.4x105 elongated cells/35-mm culture dish (Falcon type 3001). The culture dishes had been preincubated overnight with 4% FCS in medium 199. The basic culture medium consisted of HEPES-buffered medium 199 with Earle's salts, 5 mmol/l creatine, 2 mmol/l L-carnitine, 5 mmol/l taurine, 100 IU/ml penicillin, and 100 µg/ml streptomycin. To prevent growth of non-myocytes, media were also supplemented with 10 µmol/l cytosine-β-D-arabinofuranoside.

Four hours after plating, cultures were washed twice with culture medium to remove round and non-attached cells and supplied with basic culture medium supplemented with 20% fetal calf serum, in which cells were incubated for 6 days at 37 °C. The subsequent experiments were carried out in basic culture medium under serum free conditions (control), with additions of phenylephrine, isoprenaline, or phorbol myristate acetate, at concentrations indicated. Ascorbic acid (100 µmol/l) was added to all cultures as an antioxidant.

2.2. Incorporation of [14C]phenylalanine
Incorporation of phenylalanine into cells was determined by exposing cultures to L-[14C]phenylalanine (0.1 µCi/ml) for 24 h and determination of the incorporation of radioactivity into acid-insoluble cell mass as described before [13]. Non-radioactive phenylalanine (0.3 mM) was added to the medium to minimize variations in the specific activity of the precursor pool responsible for protein synthesis. As shown previously, there is a linear increase in [14C]phenylalanine incorporation into cellular protein during 24 h [13]. In incorporation studies, experiments were terminated by removal of the supernatant medium from the cultures and washed three times with ice-cold phosphate-buffered saline (PBS; composition in mM: 1.5 KH2PO4, 137 NaCl, 2.7 KCl, and 1.0 Na2HPO4, pH 7.4). Subsequently, ice-cold 10% (w/v) trichloroacetic acid was added. After storage overnight at 4 °C, the acid was removed from the dishes. Radioactivity contained in this acid fraction was taken to present the intracellular precursor pool. The dishes were then washed twice with ice-cold PBS. The remaining precipitate on the culture dishes was dissolved in 1 N NaOH/0.01% (w/v) sodium dodecyl sulfate (SDS) by an incubation for 2 h at 37 °C. In these samples DNA contents [16] were determined and the radioactivity was counted.

2.3. Quantification of intracellular pH
To measure cytosolic pH, cardiomyocytes were loaded with BCECF as described by Ladilov et al. [17]. For loading, cells attached to glass coverslips were incubated for 30 min in medium 199 with the acetoxymethyl ester of BCECF (1.5 µM). After loading, the cells were washed twice with medium 199. The washing step was followed by a 15-min post-incubation period in medium 199 to allow hydrolysis of the acetoxymethyl esters within the cell. The fluorescence from dye-loaded cells was 20–30 times higher than background fluorescence from unloaded cells. The coverslip with the loaded cells was introduced into a temperature-controlled (37 °C), transparent perfusion chamber positioned in the light path of an inverted microscope (Diaphot TMD, Nikon). Cells were superfused at a flow-rate of 0.5 ml/min with modified bicarbonate-free Tyrode's solution containing (in mmol/l): 140.0 NaCl, 2.6 KCl, 1.2 KH2PO4, 1.2 MgSO4, 1.0 CaCl2, 3.0 glucose and 25.0 HEPES, pH 7.4). Alternating excitation of the fluorescence dye by wavelengths of 440 and 490 nm for BCECF was performed with an AR-Cation measurement system adapted to the microscope (Spex Industries). Emitted light (520–560 nm) from a 10x10-µm area within a single fluorescent cell was collected by the photomultiplier of the Spex system. The light signal was recorded and analyzed by an IBM PC/AT-based data analysis system (model DM3000CM, Spex Industries). Calibration of the BCECF ratio signal was performed, as previously described by Koop and Piper [18], with 10 µg/ml nigericin, a K+–H+ ionophore, and incubation media with various pH values.

2.4. Determination of ERK2 activation
The determinations of ERK2 were done as described previously [19]. Briefly, after stimulation, cells were lysed in lysis buffer (composition: 50 mM Tris–Cl, pH 6.7, 2% (w/v) sodium dodecylsulfate, 2% (v/v) mercaptoethanol, 1 mM sodium orthovanadate). Then, nucleic acids were digested with benzonase (Merck, Darmstadt, Germany). After SDS-PAGE (100 µg protein/slot), proteins were transferred on an Immobilon-P membrane by semidry blotting. The sheets were saturated with 2% (w/v) bovine serum albumin and incubated for 2 h with rabbit polyclonal anti rat ERK2 (10 µg/50 ml, Santa Cruz Biotechnology, USA). After washing, sheep anti-rabbit IgG alkaline phosphatase-labelled (50 mU/50 ml) was added for 2 h. Detection was done by alkaline phosphatase activity recognized by 5-bromo-4-chloro-3-indolyl phosphate and nitro blue tetrazolium. For quantification the blots were densitometricially scanned and the results expressed as the ratio of the upper band, with retarded gel mobility of activated and phosphorylated ERK2, to the total amount of ERK2 determined on the Western blots.

2.5. Statistics
Data are given as means±S.E. from n different culture preparations. Statistical comparisons were performed by one-way analysis of variance and use of the Student–Newman–Keuls test for post hoc analysis [20]. Differences with P<0.05 were regarded as statistically significant.


   3. Materials
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Materials
4. Results
 5. Discussion
 Acknowledgments
 References
 
Falcon tissue culture dishes were obtained from Becton-Dickinson (Heidelberg, Germany). Boehringer Mannheim (Mannheim, Germany) was the source for glutamine-free medium 199 and fetal calf serum. Cytosine-β-D-arabinofuranoside, L-carnitine, creatine, taurine, L-phenylephrine hydrochloride, phorbol myristate acetate, and DL-isoproterenol hydrochloride were obtained from Sigma (Deisenhofen, Germany). HOE694 was a gift from Aventis AG, Frankfurt, Germany. All other chemicals were of analytical grade.


   4. Results
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Materials
 4. Results
5. Discussion
 Acknowledgments
 References
 
4.1. The influence of HOE694 on [14C]-phenylalanine incorporation
As a parameter of protein synthesis, [14C]phenylalanine incorporation into cell protein was determined during 24-h incubations. In these cultures of adult ventricular cardiomyocytes, which were pre-treated for 6 days with fetal calf serum, stimulation of either β- and {alpha}-adrenoceptors by isoprenaline and phenylephrine, respectively, increased protein synthesis in a concentration-dependent manner (Fig. 1). In the subsequent experiments phenylephrine was used at 10 µM and isoprenaline at 1 µM. HOE694 (1 µM) abolished the hypertrophic responses caused by {alpha}- and β-adrenoceptor stimulation (Fig. 2). It did not reduce the basal [14C]-phenylalanine incorporation (Fig. 2). Phorbol myristate acetate (PMA, 100 nM), a direct activator of protein kinase C used to mimic {alpha}-adrenoceptor stimulation, increased [14C]phenylalanine incorporation also (Fig. 2). This response to PMA was also attenuated in the presence of HOE694.


Figure 1
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  		Fig. 1 Protein synthesis (14C-phenylalanine incorporation) of cardiomyocytes in the absence or presence of increasing concentrations of isoprenaline (ISO) or phenylephrine (PE). Data are expressed relative to the basal values of untreated control cultures (100% value). Data are means±S.E. from n=4 cultures.

 


Figure 2
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  		Fig. 2 Protein synthesis (14C-phenylalanine incorporation) of cardiomyocytes in the absence (open bars) and presence (filled bars) of HOE694 (1 µM) under phenylephrine (10 µM), isoprenaline (1 µM), or phorbol myristate acetate (PMA, 100 nM). Data are expressed relative to the basal values of untreated control cultures (100% value). Data are means±S.E. from n=32 cultures. *P<0.05 vs. control.

 
Special efforts were made to exclude unspecified effects of HOE694. First, it was tested whether HOE694 influences basal protein synthesis. At the concentration used in this study it did not (Fig. 2), but at a 10-fold higher concentration (10 µM) it reduced the basal [14C]-phenylalanine incorporation by 17±4% (n=4, P<0.05). Second, it was analyzed whether HOE694 exerts a direct {alpha}-adrenoceptor antagonistic effect. Phenylephrine and phorbol myristate acetate activated ERK2. The presence of HOE694 did not change these effects (Fig. 3). In contrast, an {alpha}-adrenoceptor antagonistic effect was found for 5-methyl urapidil (30 nM), an {alpha}1A-adrenoreceptor antagonist. Phenylephrine increased the ratio of phosphorylated to non-phosphorylated ERK2 by 42±13% within 15 min (n=3, P<0.05 vs. control), and this response was significantly attenuated in the co-presence of the 5-methyl urapidil to 1±3% (n=3, not significantly different from control values).


Figure 3
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  		Fig. 3 Activation of ERK2 in cardiomyocytes. Cells were either used without additions to the media (control, C) or treated for 15 min with phenylephrine (PE, 10 µM), phorbol myristate acetate (PMA, 100 nM), HOE694 (HOE, 1 µM), or combinations of them. Activation of ERK2 is indicated by the appearance of an upper band caused by phosphorylation and subsequent activation of the kinase. The figure shows a representative Western blot obtained by incubation with an ERK2 antibody.

 
4.2. Cytosolic pH in cardiomyocytes under hypertrophic stimulation
In the presence of phenylephrine, isoprenaline, and phorbol myristate acetate, HOE694 attenuated the stimulation of protein synthesis. This suggests an activation of NHE-1 under these conditions. In the presence of either of these agonists, the intracellular pH was continuously monitored for 30 min. In cardiomyocytes, superfused with bicarbonate-free medium supplemented with phenylephrine a cellular alkalization was observed, which was diminished by the co-presence of HOE694 (Table 1). In contrast, neither phorbol myristate acetate nor isoprenaline changed pHi (Table 1). Addition of phenylephrine subsequent to phorbol myristate acetate or isoprenaline again caused a cellular alkalization (Fig. 4).


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  		Table 1 Changes in intracellular pH in bicarbonate free media

 


Figure 4
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  		Fig. 4 Intracellular pH (pHi) of cardiomyocytes. (a) Cells were superfused with experimental media containing phorbol myristate acetate (PMA, 100 nM) and for the last 20 min with phenylephrine (PE, 10 µM) in addition. Data indicate means±S.E. from n=3 experiments. *P<0.05 vs. control values (time 0). (b) Cells were superfused with experimental media containing isoprenaline (ISO, 1 µM) and for the last 20 min with phenylephrine (PE, 10 µM) in addition. Data indicate means±S.E. from n=3 experiments. *P<0.05 vs. control values (time 0).

 

   5. Discussion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Materials
 4. Results
 5. Discussion
Acknowledgments
 References
 
It was shown in this study on cardiomyocytes with hypertrophic responsiveness to {alpha}- or β-adrenoceptor stimulation that HOE694 attenuates the hypertrophic growth response to either stimulation. Since the only known effect of HOE694 is its inhibitory effect on NHE-1 activation, this may indicate that NHE-1 activation is part of the signaling elements leading to stimulation of protein synthesis, irrespective of the hypertrophic stimulus used and the second messenger systems involved. The main finding of this study is that the mechanism by which HOE694 attenuates the induction of protein synthesis is independent from intracellular alkalization which accompanies NHE-1 activation in case of {alpha}-adrenoceptor stimulation but not under β-adrenoceptor stimulation.

The {alpha}-adrenoceptor mediated hypertrophic growth effect in ventricular cardiomyocytes from adult rats has been described before. It depends on the activation of PKC, PI3-kinase, and p70s6k [3–5]. In our initial study on newly isolated cardiomyocytes, which shows a hypertrophic responsiveness to {alpha}- but not β-adrenoceptor stimulation, we demonstrated that use of the pharmacological inhibitor of NHE-1, HOE694, attenuates the hypertrophic growth response to {alpha}-adrenoceptor stimulation [9]. NHE-1 activation by {alpha}-adrenoceptor stimulation also caused cellular alkalization. This study confirmed on cultured cardiomyocytes with hypertrophic responsiveness to {alpha}- and β-adrenoceptor stimulation that cytosolic alkalization occurs upon {alpha}-adrenoceptor stimulation. This is in line with recent observations that the intracellular signaling induced by {alpha}-adrenoceptor stimulation is not changed in serum cultured cardiomyocytes. Cellular alkalization caused by phenylephrine occurs in a PKC-independent way, since direct activation of PKC with phorbol myristate acetate does not cause such alkalization. These findings are in agreement with a previous report from Puceat et al. [21], who also found on adult ventricular cardiomyocytes no evidence for an involvement of PKC in the {alpha}-adrenoceptor induced modulation of pHi. Wallert and Fröhlich [22], however, reported conflicting results. They showed that cellular alkalization occurred under phorbol myristate acetate in ventricular cardiomyocytes isolated from adult rats. The explanation for this difference is not clear. It may be important that we and Puceat et al. used attached cardiomyocytes whereas Wallert and Fröhlich used cells in suspension.

It has previously been shown that induction of protein synthesis under {alpha}-adrenoceptor stimulation depends on PKC-activation and can therefore be simulated by phorbol myristate. It is now found that the presence of the NHE-1 inhibitor HOE694 attenuates the hypertrophic effects of either {alpha}-adrenoceptor stimulation or direct PKC activation. As the latter was not accompanied by cytosolic alkalization, the PKC-dependent growth response must be independent from the pHi changes seen under {alpha}-adrenoceptor stimulation.

As shown before in this model of cultured cardiomyocytes isolated from adult rats, the β-adrenoceptor mediated hypertrophic growth effect depends on the activation of cycloAMP-dependent protein kinase (PKA), PI3-kinase, and p70s6k [4,5,15]. We report here that the growth effects caused by β-adrenoceptor stimulation are sensitive to the NHE-1 inhibitor HOE694. Cellular alkalization did not occur in the presence of β-adrenoceptor stimulation. In this model therefore, growth effects caused by direct stimulation of PKC or β-adrenoceptor stimulation are independent of pHi changes but sensitive to inhibition of NHE-1 by HOE694. It is in line with these observations, that we have recently shown that cellular alkalization leads to an increase in creatine phosphate but that this increase is not causally involved in the acceleration of protein synthesis. Therefore, activation of NHE-1 seems to be required for the growth response of cardiomyocytes to different growth factors but changes in pHi do not represent the signaling step.

In cardiomyocytes directly pretreated with TGF-β, or precultured with fetal calf serum or low concentrations of isoprenaline, {alpha}- and β-adrenoceptor stimulation leads to increases in protein synthesis. Although the second messengers involved in these responses differ, i.e. activation of either PKC or PKA, other intracellular steps required for hypertrophic growth are the same. These are PI3-kinase, p70s6k, and, as shown in this study, NHE-1. At present, we can only speculate about the mechanism by which NHE-1 activation leads to an induction of protein synthesis. However, NHE-1 co-localizes with actin at the membrane and this may indicate that NHE-1/actin interactions may be relevant for transition of the signaling cascade from the membrane to the cytoplasma [23,24]. Indeed, we found preliminary evidence that inhibition of NHE-1 interferes with actin architecture in cardiomyocytes (data not shown).

One may suggest that the observed effects of HOE694 on protein synthesis are unspecific effects even though HOE694 is known as a highly specific inhibitor of the NHE-1. However, unspecified effects of HOE694 due to general inhibition of protein synthesis and cross-reactivity with {alpha}-adrenoceptor stimulation have been excluded in our study. First, a low concentration of HOE694 as used in our study was without an influence on basal rate of protein synthesis. Second, HOE694 did not interfere with ERK2 activation under {alpha}-adrenoceptor stimulation, that represents another {alpha}-adrenoceptor mediated intracellular signaling pathway independent from the regulation of protein synthesis. Therefore, HOE694 used at 1 µM as done in our study, was sufficient to inhibit NHE-1 but did not interfere with adrenoceptor binding. We can not exclude the possibility that HOE694 interacts with signaling steps activated by either {alpha}- or β-adrenoceptor stimulation which are different from NHE-1, but at present no such interactions are known.

In summary, {alpha}- or β-adrenoceptor stimulation activates protein synthesis in cultured adult ventricular cardiomyocytes in a NHE-1 dependent way but independently of pHi changes.


   Acknowledgments
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Materials
 4. Results
 5. Discussion
 Acknowledgments
References
 
This study was supported by the Deutsche Forschungsgemeinschaft (DFG), grant SCHL 324/4-1. This work is part of the thesis submitted by M. Schäfer.


   References
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Materials
 4. Results
 5. Discussion
 Acknowledgments
 References
 

  1. Morgan H.E, Baker K.M. Cardiac hypertrophy: mechanical, neural and endocrine dependence. Circulation (1991) 83:13–25.[Free Full Text]
  2. Schlüter K.-D, Miller B.C, McDermott B.J, Piper H.M. Regulation of protein synthesis and degradation in adult ventricular cardiomyocytes. Am J Physiol (1995) 269:C1347–1355.[Web of Science][Medline]
  3. Schlüter K.-D, Piper H.M. Trophic effects of catecholamines and parathyroid hormone on adult ventricular cardiomyocytes. Am J Physiol (1992) 263:H1739–1746.[Web of Science][Medline]
  4. Schlüter K.-D, Goldberg Y, Taimor G, Schäfer M, Piper H.M. Role of phosphatidylinositol 3-kinase activation in the hypertrophic growth of adult ventricular cardiomyocytes. Cardiovasc Res (1998) 40:174–181.[Abstract/Free Full Text]
  5. Simm A, Schlüter K.-D, Diez C, Piper H.M, Hoppe J. Activation of p70s6 kinase by β-adrenoceptor agonists on adult cardiomyocytes. J Mol Cell Cardiol (1998) 30:2059–2067.[CrossRef][Web of Science][Medline]
  6. Schlüter K.-D, Piper H.M. Regulation of growth in the adult cardiomyocytes. FASEB J (Suppl.) (1999) 13:S17–22.[Web of Science][Medline]
  7. Hori M, Nakatsubo N, Kagiya T, et al. The role of Na+/H+ exchange in norepinephrine-induced synthesis in neonatal cultured rat cardiomyocytes. Jpn J Circ (1990) 54:535–539.
  8. Fuller S.J, Gaitanaki C.J, Hatchett R.J, Sugden P.H. Acute {alpha}1-adrenenergic stimulation of cardiac protein synthesis may involve increased intracellular pH and protein kinase activity. Biochem J (1991) 273:347–353.[Web of Science][Medline]
  9. Schlüter K.-D, Schäfer M, Balser C, Taimor G, Piper H.M. Influence of pHi and creatine phosphate on {alpha}-adrenoceptor-mediated cardiac hypertrophy. J Mol Cell Cardiol (1998) 30:763–771.[CrossRef][Web of Science][Medline]
  10. Fuller S.J, Gaitanaki C.J, Sugden P.H. Effects of increasing extracellular pH on protein synthesis and protein degrdadation in the perfused working rat heart. Biochem J (1989) 259:173–179.[Web of Science][Medline]
  11. Clark W.A, Rudnick S.J, LaPres J.J, Lesch M, Decker R.S. Hypertrophy of isolated adult feline heart cells following β-adrenergic-induced beating. Am J Physiol (1991) 261:C530–542.[Web of Science][Medline]
  12. Dubus I, Samuel J.-L, Marott F, Delcayre C, Rappaport L. Adrenergic agonists stimulate the synthesis of noncontractile but not contractile proteins in cultured myocytes isolated from adult rat heart. Circ Res (1990) 66:867–874.[Abstract/Free Full Text]
  13. Pinson A, Schlüter K.-D, Zhou X.J, Schwartz P, Kessler-Icekson G, Piper H.M. Alpha and beta-adrenergic stimulation of protein synthesis in cultured adult ventricular cardiomyocytes. J Mol Cell Cardiol (1993) 25:477–490.[CrossRef][Web of Science][Medline]
  14. Schlüter K.-D, Zhou X.J, Piper H.M. Induction of hypertrophic responsiveness to isoprenaline by TGF-β in adult rat cardiomyocytes. Am J Physiol (1995) 269:C1311–1316.[Web of Science][Medline]
  15. Zhou X.J, Schlüter K.-D, Piper H.M. Hypertrophic responsiveness to β2-adrenoceptor stimulation on adult ventricular cardiomyocytes. Mol Cell Biochem (1996) 164:211–216.[CrossRef][Web of Science]
  16. Giles K.W, Myers A. An improved diphenylamine method for the estimation of deoxyribonucleic acid. Nature (1965) 206:93.[Medline]
  17. Ladilov Y.V, Siegmund B, Balser C, Piper H.M. Simulated ischemia increases the susceptibility of rat cardiomyocytes to hypercontracture. Circ Res (1997) 80:69–75.[Abstract/Free Full Text]
  18. Koop A, Piper H.M. Protection of energy status of hypoxic cardiomyocytes by mild acidosis. J Mol Cell Cardiol (1992) 24:55–65.[Web of Science][Medline]
  19. Schlüter K.-D, Simm A, Schäfer M, Taimor G, Piper H.M. Early response kinase and PI 3-kinase activation in adult cardiomyocytes and their role in hypertrophy. Am J Physiol (1999) 276:H1655–1663.[Web of Science][Medline]
  20. Godfrey K. Comparing the means of several groups. N Engl J Med (1985) 313:1450–1456.[Abstract]
  21. Puceat M, Clement-Chomienne O, Terzic A, Vassort G. Alpha 1-adrenoceptor and purinoceptor agonists modulate Na–H antiport in single cardiac cells. Am J Physiol (1993) 264:H139–310.
  22. Wallert M.A, Fröhlich O. Alpha 1-adrenergic stimulation of Na–H exchange in cardiac myocytes. Am J Physiol (1992) 263:C1096–1102.[Web of Science][Medline]
  23. Grinstein S, Woodside M, Waddell T.K, et al. Focal localization of the NHE-1 isoform of the Na+/H+ antiport: assessment of effects on intracellular pH. EMBO J (1993) 12:5209–5218.[Web of Science][Medline]
  24. Goss G.G, Woodside M, Wakabayashi S, et al. ATP dependence of NHE-1, the ubiquitous isoform of the Na+/H+ antiporter. Analysis of phosphorylation and subcellular localization. J Biol Chem (1994) 269:8741–8748.[Abstract/Free Full Text]

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