Related Experiment Videos
Effects of isoproterenol on cyclic AMP and cyclic AMP-dependent protein kinase in developing chick myocardium
Insights
Cyclic AMP-dependent protein kinase activity in chick hearts changes during development. Phosphodiesterase activity, not cyclase, influences isoproterenol
Area of Science:
- Cardiovascular Physiology
- Developmental Biology
- Molecular Pharmacology
Background:
- Cyclic AMP-dependent protein kinase (PKA) plays a crucial role in cardiac function.
- The developmental regulation of PKA activity and its response to stimuli in the embryonic and neonatal heart are not fully understood.
- Understanding these changes is vital for comprehending cardiac maturation and response to stress.
Purpose of the Study:
- To investigate the developmental changes in cyclic AMP-dependent protein kinase activity in embryonic and newborn chick myocardium.
- To assess the endogenous activation state of PKA using activity ratios.
- To examine the effects of isoproterenol on cyclic AMP levels and PKA activation during cardiac development.
Main Methods:
- DEAE-cellulose chromatography was used to assess PKA activity in myocardial homogenates.
- Activity ratios (activity without cyclic AMP/activity with cyclic AMP) were employed to determine the enzyme's activation state.
- Cyclic AMP levels, adenylate cyclase, and phosphodiesterase activities were measured in response to isoproterenol.
Main Results:
- Embryonic and newborn chick myocardia exhibit a major peak of cyclic AMP-dependent PKA activity.
- Newborn chick myocardium has lower cyclic AMP content and reduced baseline PKA activity compared to embryonic myocardium.
- Isoproterenol elicits smaller elevations in cyclic AMP and PKA activity in newborn compared to embryonic chick hearts, attributed to altered phosphodiesterase metabolism.
Conclusions:
- The developmental decrease in responsiveness to isoproterenol in chick myocardium is linked to changes in cyclic AMP metabolism, specifically phosphodiesterase activity.
- Phosphodiesterase activity, rather than adenylate cyclase, is the primary determinant of altered cyclic AMP signaling during cardiac development.
- These findings highlight the critical role of cyclic nucleotide metabolism in regulating cardiac function during development.
Abstract:
Embryonic chick (7-9 day) and newborn chick myocardia contain one major peak of cyclic AMP-dependent protein kinase activity as assessed by DEAE-cellulose chromatography. Evidence is presented that the cyclic AMP-dependent protein kinase activity ratios (activity in absence of cyclic AMP/activity in presence of added cyclic AMP) of homogenates prepared with low ionic strength buffer reflect the endogenous activation state of the enzyme. The cyclic AMP content of newborn chick myocardium is lower than that of 7--9 day embryonic chick myocardium; the baseline cyclic AMP-dependent protein kinase activity is correspondingly reduced. Isoproterenol produces smaller elevations in cyclic AMP and in the cyclic AMP-dependent protein kinase activity ratio of newborn chick as compared to embryonic chick myocardium. Differences in the ability of isoproterenol to elevate cyclic AMP in the different preparations are not accompanied by appropriate changes in the adenylate cyclase or phosphodiesterase activities of the corresponding broken cell preparations. Studies with the phosphodiesterase inhibitor, Ro 20 1724 indicate that the changes in the ability of isoproterenol to elevate cyclic AMP in the developing chick myocardium are due to changes in the metabolism of the cyclic nucleotide by phosphodiesterase.