Related Experiment Videos
Ouabain-induced hypertrophy in cultured cardiac myocytes is accompanied by changes in expression of several late
Abstract:
Partial inhibition of cardiac Na/K-ATPase by digitalis drugs such as ouabain is the initial event leading to positive inotropy in the heart. We showed recently that exposure of rat cardiac myocytes to ouabain concentrations that produce positive inotropy, but no overt toxicity, caused inductions of some early response genes and hypertrophy of these myocytes. The aim of this work was to determine if ouabain also affects the expressions of certain late response genes that are regulated by other hypertrophic stimuli. Non-toxic concentrations of ouabain (5-100 microM) increased mRNAs of skeletal alpha-actin, atrial natriuretic factor, myosin light chain 2, and transforming growth factor beta: indicating that ouabain's effects on these marker genes are similar to those of hypertrophic stimuli that mimic the effects of pressure overload. Expression of skeletal alpha-actin was more sensitive to ouabain than that of atrial natriuretic factor, suggesting significant differences in the ouabain-specific pathways of the induction of these fetal genes. The effects of ouabain on skeletal alpha-actin gene were transcriptional, and required an increase in net influx of extracellular Ca2+. Protein kinase C and Ca(2+)-calmodulin kinases, but not protein kinase A, were involved in the signal pathways leading to the induction of skeletal alpha-actin gene. These data and our prior findings indicate that an increase in net influx of Ca2+ through partial inhibition of Na/K-ATPase initiates protein kinase-dependent pathways resulting in alterations in cardiac growth and expressions of both early and late response genes.
Insights
Ouabain, a cardiac drug, triggers heart cell growth and gene changes by partially blocking Na/K-ATPase. This process involves increased calcium influx and specific protein kinases, affecting both early and late gene responses.
Area of Science:
- Cardiology
- Molecular Biology
- Cellular Physiology
Background:
- Digitalis drugs, like ouabain, partially inhibit cardiac Na/K-ATPase, initiating positive inotropy.
- Previous studies showed ouabain induces early response genes and hypertrophy in rat cardiac myocytes at non-toxic concentrations.
Purpose of the Study:
- To investigate whether ouabain affects the expression of late response genes in cardiac myocytes.
- To compare ouabain's effects on late response genes with those of other hypertrophic stimuli.
Main Methods:
- Exposure of rat cardiac myocytes to non-toxic ouabain concentrations (5-100 microM).
- Measurement of mRNA levels for skeletal alpha-actin, atrial natriuretic factor, myosin light chain 2, and transforming growth factor beta.
- Analysis of the role of extracellular calcium influx, protein kinase C, Ca(2+)-calmodulin kinases, and protein kinase A in gene induction.
Main Results:
- Ouabain increased mRNAs of skeletal alpha-actin, atrial natriuretic factor, myosin light chain 2, and transforming growth factor beta.
- Skeletal alpha-actin expression was more sensitive to ouabain than atrial natriuretic factor.
- Ouabain's effects on skeletal alpha-actin gene expression were transcriptional, dependent on increased extracellular Ca2+ influx, and involved Protein kinase C and Ca(2+)-calmodulin kinases.
Conclusions:
- Ouabain, at non-toxic concentrations, induces cardiac late response genes similarly to other hypertrophic stimuli.
- Increased net influx of extracellular Ca2+ and subsequent activation of protein kinase-dependent pathways mediate ouabain's effects on cardiac gene expression and growth.