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Preproenkephalin mRNA expression in developing rat heart and in cultured ventricular cardiac muscle cells
1Department of Biochemistry and Molecular Biology, Louisiana State University Medical Center, New Orleans 70112.
Abstract:
Heart muscle tissue has previously been reported to have the highest content of preproenkephalin (ppEnk) mRNA of any tissue in the adult rat. We have determined that it is present in the ventricular cardiac muscle cells of the heart and is developmentally regulated. The expression of ppEnk mRNA was observed to be low throughout the first 2 weeks of postnatal development and decreases substantially during week 3. Expression was again low by week 4, but by adulthood (approx. 3 months), it reached a maximum. ppEnk mRNA was actively expressed in primary cardiac muscle cell cultures prepared from both neonatal and adult rats. Its steady-state content in cell cultures was observed to be increased by cyclic AMP and 3-isobutyl-1-methylxanthine. The phorbol ester phorbol 12-myristate 13-acetate elicited a transient effect (i.e. an increase was observed at 4 h and a return to control values by 24 h). We speculate that enkephalin may play a multi-functional role in the differentiation of neonatal cardiac muscle cells and in the terminally differentiated adult heart cell. We demonstrate that the primary culture systems employed in this study will be useful models with which to explore both transcriptional and translational regulation of ppEnk mRNA in the heart.
Insights
Heart muscle cells express preproenkephalin (ppEnk) mRNA, with levels changing during development and adulthood. Cyclic AMP and other compounds affect ppEnk mRNA levels in cultured heart cells.
Area of Science:
- Cardiovascular Biology
- Molecular Cardiology
- Neuroendocrinology
Background:
- Heart muscle tissue exhibits the highest preproenkephalin (ppEnk) mRNA levels in adult rats.
- ppEnk mRNA is present in ventricular cardiac muscle cells and is developmentally regulated.
Purpose of the Study:
- To investigate the developmental regulation of ppEnk mRNA expression in rat cardiac muscle.
- To examine the effects of various compounds on ppEnk mRNA levels in primary cardiac muscle cell cultures.
- To explore the potential roles of enkephalin in cardiac muscle cell differentiation and function.
Main Methods:
- Quantitative analysis of ppEnk mRNA expression in rat hearts at different developmental stages.
- Primary cell culture of neonatal and adult rat cardiac muscle cells.
- Treatment of cultured cells with cyclic AMP, 3-isobutyl-1-methylxanthine, and phorbol 12-myristate 13-acetate.
Main Results:
- ppEnk mRNA expression is low in early postnatal development, decreases during the third week, and peaks in adulthood.
- ppEnk mRNA is actively expressed in both neonatal and adult cardiac muscle cell cultures.
- Cyclic AMP and 3-isobutyl-1-methylxanthine increase steady-state ppEnk mRNA content, while phorbol 12-myristate 13-acetate has a transient effect.
Conclusions:
- Enkephalin may have diverse roles in neonatal cardiac muscle cell differentiation and adult heart cell function.
- Primary cardiac muscle cell culture systems are valuable for studying ppEnk mRNA regulation in the heart.