Cell density and contraction regulate p38 MAP kinase-dependent responses in neonatal rat cardiac myocytes.
In vitro cardiac myocyte hypertrophy is characterized by increased cell size, sarcomere organization, and induction of several genes including atrial natriuretic factor (ANF). The hypertrophic growth program has been associated with activation of various mitogen-activated protein kinase (MAP) kinase family members, one of which is a stress kinase, p38. In this study, we found that the p38-specific inhibitor SB-203580 failed to inhibit phenylephrine-induced ANF-driven gene expression in low-density myocyte cultures but did inhibit gene expression in higher density cultures. Dense myocyte cultures also had a higher metabolic activity and contraction rate than cells plated at low density. We found that mimicking this effect by rapid electrical pacing activated ANF-driven gene expression and that this expression was inhibited by inactivation of p38. However, addition of SB-203580 at time points ranging between 1 and 72 h suggests that the effect of p38 on the ANF promoter may be both direct and indirect. Electrical pacing induced a small, but consistent, increase in p38 phosphorylation (phospho-p38) at time points ranging from 30 min to 4 h, but at later times phospho-p38 levels were reduced. When myocytes were treated with phenylephrine or electrically paced in the presence of the p38 inhibitor, there was little discernible change in morphology or rates of protein synthesis from DMSO-treated cells at 48 or 72 h. These data indicate that cell density and myocyte contraction may modulate p38-dependent pathways for ANF gene expression, but these pathways may not be direct and have limited effects on hypertrophic morphology.
Hines
W A
WA
Department of Human Genetics, Program in Human Molecular Biology and Genetics, Departments of Oncological Sciences, Human Genetics, and Internal Medicine, University of Utah, Salt Lake City, Utah 84112, USA.
Thorburn
J
J
Thorburn
A
A
D000818:Animals; D000831:Animals, Newborn; D009320:Atrial Natriuretic Factor / Q000502:physiology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism / Q000502:physiology*; D002452:Cell Count / Q000187:drug effects; D002478:Cells, Cultured; D004558:Electric Stimulation; D015870:Gene Expression; D006321:Heart / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology*; D010656:Phenylephrine / Q000494:pharmacology; D010766:Phosphorylation; D051381:Rats; D048051:p38 Mitogen-Activated Protein Kinases
D010656:Phenylephrine; D009320:Atrial Natriuretic Factor; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases