Suspension culture of differentiated rat heart myocytes on non-adhesive surfaces

Cocaine activates calcium/calmodulin kinase II and causes cardiomyocyte hypertrophy

Cardiac hypertrophy occurs in as many as 47% of normotensive individuals who chronically use cocaine. We investigated the effects of cocaine, in concentrations commonly found in chronic cocaine users, on calcium/calmodulin kinase (CaMK), and whether cocaine can activate CaMK, increase cardiac myocyte protein expression, and cause cardiac hypertrophy in this manner. In series I to III, 0 (control) or cocaine in concentrations of 10 to 10 mol/L was added to cultured adult rat cardiac ventricular myocytes to determine by Western blots and by P incorporation the optimal treatment time and the optimal dose for CaMK activation. In series I, cocaine, 10 mol/L, increased myocyte CaMKII translocation from myocyte soluble to particulate fractions by > or =73 +/- 9% (P < 0.01) in comparison with controls but did not cause the translocation of CaMKI or CaMKIV. In series II and III, cocaine treatment of myocytes for 15 minutes increased maximal CaMKII activity by 86.5 +/- 13.3% (P < 0.001) and a cocaine dose of 5 x 10 mol/L increased CaMKII activity by 169.5 +/- 18.1% (P < 0.001). In series IV we measured by silver staining beta-myosin heavy chain protein (beta-MHC) expression in myocytes before and after cocaine and also CaMK inhibition with KN-62 (1-[N,O-bis-(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine). In these experiments, cocaine, 5x10 mol/L, increased myocyte protein concentration by 29.2 +/- 2.8%, and beta-MHC by 93.2 +/- 8.8% (P < 0.001). In series V and VI, cocaine effects on calcium currents (ICa) and intracellular Ca ([Ca]i) were determined before and after CaMK inhibition with KN-62 in rat myocytes. Cocaine, 10 mol/L, enhanced ICa peak amplitude in a voltage-dependent manner (by 173.9 +/- 14.9% at -20 mV and by 38.4 +/- 6.9% at 0 mV P < 0.01). Cocaine, 10 to 10 mol/L, in series VI promoted Ca transients from myocyte sarcoplasmic reticulum and increased [Ca]i to 607 +/- 141 x 10 mol/L (P < 0.05). KN-62 decreased cocaine-induced myocyte protein expression by 76.6%, and beta-MHC by 66.2% (P < 0.01) and significantly decreased cocaine-induced Ca transients and [Ca]i. We conclude that CaMKII activation is an important mechanism whereby cocaine can cause myocyte hypertrophy.

Cocaine produces cardiac hypertrophy by protein kinase C dependent mechanisms

BACKGROUND

Chronic cocaine users can have as much as a 69% increase in left ventricular muscle mass without associated increases in arterial blood pressure, heart rate, renin, aldosterone, or cortisol. We determined whether cocaine directly increases cardiomyocyte protein content and whether protein kinase C is important in this process.

METHODS AND RESULTS

Adult rat cardiomyocytes were isolated and grown in cultures. In Series I experiments, cocaine, 10(-8) to 10(-6) M, or vehicle, in the absence or presence of phentolamine or metoprolol, was added to each culture and the cells were subsequently harvested. In Series II, cocaine, 10(-6) M, cocaine, 10(-6) M, plus bisindolylmaleimide, 10(-6) M, a protein kinase C inhibitor, or vehicle were added to each culture and the cells subsequently harvested. We determined the total protein content, the content of alpha-myosin and fetal beta-myosin heavy-chain protein, and the presence of protein kinase C isoforms in the cardiomyocyte soluble and particulate fractions. Protein kinase C translocation from the soluble to particulate fraction is indicative of activation. In Series III, we determined the cocaine effects on ERK, SAPK/JNK, and p38. In Series I, cocaine, 10(-8) to 10(-6) M, dose-dependently increased myocyte protein content by as much as 28%+/-2% (P<.001) and fetal beta-myosin heavy-chain protein content by 80%+/-2% (P<.001). Neither phentolamine nor metoprolol inhibited this process. In Series II, we determined that ventricular myocytes contain alpha (alpha), beta (beta), delta (delta), epsilon (epsilon), and zeta (zeta) protein kinase C isoforms. Cocaine, 10(-6) M, caused a 45+/-5% increase (P<.001) in protein kinase Calpha in the particulate fraction. The addition of a protein kinase C inhibitor to the myocyte cultures prevented the cocaine-induced translocation of protein kinase Calpha and limited the increase in beta-myosin heavy-chain protein content by >75% (P<.001). However, cocaine did not increase the phosphorylation of ERK, SAPK/JNK or p38 in Series III.

CONCLUSIONS

Cocaine increases adult cardiomyocyte protein content by protein kinase Calpha-dependent mechanisms, and this process can contribute to the cardiac hypertrophy and cardiomyopathy that results from chronic cocaine use.

Cocaine increases beta-myosin heavy-chain protein expression in cardiac myocytes

BACKGROUND

As many as 47% of chronic cocaine users develop cardiac ventricular hypertrophy. The presence and degree of cocaine-induced ventricular hypertrophy is not correlated with the use of other substances of abuse such as alcohol or cigarettes. Moreover, this hypertrophy occurs in individuals without sustained increases in arterial blood pressure or heart rate, or increases in the plasma concentration of renin, aldosterone, norepinephrine, or cortisol. Therefore, we investigated whether cocaine, in concentrations commonly found in cocaine users, has any direct effects on the protein content in cardiac ventricular myocytes. We compared the effects of cocaine with norepinephrine, which increases the total protein content, especially beta-myosin heavy-chain contractile protein (beta-MHC), in cardiac ventricular myocytes.

METHODS

Experiments were performed on 30-day-old rat ventricular myocytes suspended in culture media and cultured in flasks. In 12 suspension-culture experiments, cocaine or norepinephrine, in doses of 0 (control) or 10(-6) mol/L was added to each culture and the cells were harvested on day 5. In 16 flask-culture experiments, cocaine or norepinephrine was added to each culture on day 7 in doses of 0 (control-vehicle), 10(-7), or 10(-6) mol/L and the cells were harvested on day 10. The total protein content and the myosin protein expression of the myocytes in each culture were determined. Juvenile and adult rat cardiac myosin protein is predominately alpha-myosin heavy-chain protein (alpha-MHC), whereas beta-MHC occurs primarily in fetal rat hearts.

RESULTS

In the suspension-culture experiments, cocaine, 10(-6) mol/L, increased the cardiomyocyte total protein concentration by 29% +/- 2% (P <.001) and the beta-MHC expression by 81% +/- 10% (P <.01) in comparison with the control myocytes. Cocaine slightly decreased cardiomyocyte alpha-MHC. Norepinephrine increased the total protein concentration by 21% +/- 3% (P <.001) and the beta-MHC expression by 59% +/- 10% (P <.01), but did not increase alpha-MHC expression. In the flask-culture experiments, cocaine, 10(-6) mol/L, maximally increased the total protein concentration by 28% (P <.001), the protein/cell ratio by 57% +/- 10% (P <.01), and the beta-MHC expression by 85% +/- 8% (P <.01). Cocaine slightly decreased alpha-MHC. Norepinephrine, 10(-6) mol/L, maximally increased the total protein concentration by 35%, the protein/cell ratio by 63% +/- 9% (P <.01), and the expression of beta-MHC by 78% +/- 11% (P <. 01). Norepinephrine did not increase alpha-MHC expression. In 18 separate flask-culture experiments, cocaine, 10(-6) mol/L, was added to the cardiomyocyte cultures after the addition of phentolamine (n = 9), in concentrations of 10(-7) to 10(-5) mol/L, or metoprolol (n = 9), in concentrations of 10(-7) to 10(-5) mol/L. Neither phentolamine nor metoprolol inhibited the cocaine-induced increase in cardiomyocyte total protein content or the expression of beta-MHC.

CONCLUSION

Cocaine, similar to norepinephrine, significantly increases the total protein content and the expression of beta-MHC in cardiac ventricular myocytes. In this manner, cocaine may cause cardiac ventricular hypertrophy. This process is not inhibited by alpha- or beta-adrenergic receptor blockade.

Titanium dioxide ceramics control the differentiated phenotype of cardiac muscle cells in culture

A new approach, the cultivation of heart muscle cells on biocompatible scaffolds made from titanium dioxide ceramics was established to provide a mechanism for in vitro engineering of a vital heart tissue. Terminally differentiated ventricular myocytes isolated from hearts of adult rats were kept in primary culture for long periods of time and used as an experimental model. The microenvironmental properties of titanium dioxide ceramics helped to maintain the tissue-like structural organisation of the cardiac cells in vitro. Coating of the cell substrata with fine-grained titanium dioxide ceramics imitating cell surface topography favoured the formation of focal adhesion complexes in the ventral plasma membrane of cardiomyocytes. It also promoted the cellular expression of vinculin, a protein that connects the ECM integrin receptors to the network of cytoplasmic filaments, which define cell shape. This topographical reinforcement of cell-material interactions led to stabilisation of the molecular linkage between the extracellular contacts and the intracellular cytoskeleton and thus assisted the preservation and maintenance of the heart muscle cell differentiated phenotype in long-term primary culture. The results of this work demonstrate a promising pathway for the regulation of cellular organisation in vitro by local geometric control.

Cardiac tissue engineering: cell seeding, cultivation parameters, and tissue construct characterization

Cardiac tissue engineering has been motivated by the need to create functional tissue equivalents for scientific studies and cardiac tissue repair. We previously demonstrated that contractile cardiac cell-polymer constructs can be cultivated using isolated cells, 3-dimensional scaffolds, and bioreactors. In the present work, we examined the effects of (1) cell source (neonatal rat or embryonic chick), (2) initial cell seeding density, (3) cell seeding vessel, and (4) tissue culture vessel on the structure and composition of engineered cardiac muscle. Constructs seeded under well-mixed conditions with rat heart cells at a high initial density ((6-8) x 10(6) cells/polymer scaffold) maintained structural integrity and contained macroscopic contractile areas (approximately 20 mm(2)). Seeding in rotating vessels (laminar flow) rather than mixed flasks (turbulent flow) resulted in 23% higher seeding efficiency and 20% less cell damage as assessed by medium lactate dehydrogenase levels (p < 0.05). Advantages of culturing constructs under mixed rather than static conditions included the maintenance of metabolic parameters in physiological ranges, 2-4 times higher construct cellularity (p &le 0.0001), more aerobic cell metabolism, and a more physiological, elongated cell shape. Cultivations in rotating bioreactors, in which flow patterns are laminar and dynamic, yielded constructs with a more active, aerobic metabolism as compared to constructs cultured in mixed or static flasks. After 1-2 weeks of cultivation, tissue constructs expressed cardiac specific proteins and ultrastructural features and had approximately 2-6 times lower cellularity (p < 0.05) but similar metabolic activity per unit cell when compared to native cardiac tissue.