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Published on: October 15, 2014
Calcium accumulating and ATPase activity of cardiac sarcoplasmic reticulum before and after birth
Insights
Cardiac sarcoplasmic reticulum (SR) undergoes developmental changes around birth, impacting its calcium (Ca2+) accumulation and ATP hydrolysis. These findings reveal species-specific adaptations in neonatal cardiac function.
Area of Science:
- Cardiovascular Physiology
- Developmental Biology
- Cellular Biochemistry
Background:
- The cardiac sarcoplasmic reticulum (SR) is crucial for regulating intracellular calcium levels during heart muscle contraction.
- Understanding developmental changes in SR function is vital for neonatal cardiac health.
Purpose of the Study:
- To investigate developmental alterations in cardiac sarcoplasmic reticulum (SR) function around the time of birth.
- To determine how these changes affect the SR's capacity for calcium (Ca2+) accumulation and adenosine triphosphatase (ATP) hydrolysis.
Main Methods:
- Microsomal fractions rich in SR were isolated from fetal, neonatal, and adult guinea pig and rabbit hearts.
- Calcium (Ca2+) uptake and binding capacities were measured.
- Adenosine triphosphatase (ATP) hydrolysis activity was assessed, differentiating between Ca2+-dependent and Ca2+-independent enzymes.
Main Results:
- Fetal cardiac microsomes showed reduced Ca2+ accumulation (via uptake) and ATP hydrolysis prior to birth.
- Neonatal cardiac microsomes exhibited increased Ca2+-accumulating activity post-birth, with species-specific mechanisms (Ca2+ uptake in rabbits, Ca2+ binding in guinea pigs).
- An increase in Ca2+-dependent ATPase activity accompanied the enhanced Ca2+-accumulating capacity in neonates.
Conclusions:
- The cardiac SR undergoes significant developmental changes around parturition.
- These species-specific adaptations enhance the SR's Ca2+-accumulating efficiency in the neonatal heart.
- These findings provide insights into the maturation of cardiac excitation-contraction coupling.
Abstract:
The possibility that the cardiac SR undergoes developmental changes at about the time of birth, and that these changes affect its ability to accumulate Ca2+ and to hydrolyse ATP has been studied. SR-rich microsomal fractions were prepared from heart muscle excised from foetal guinea pigs and rabbits 1 day before their anticipated date of birth, and from 1 day old and adult animals. For control purposes microsomes were also prepared from the relevant maternal stock animals. One day before birth the cardiac microsomes of the foetal but not of the maternal animals exhibited a decreased ability to accumulate Ca2+ by uptake but not by the binding process, and a decreased ability to hydrolyse ATP. This reduction in ATPase activity involved both the Ca2+-dependent and the Ca2+-independent ATPase enzymes. One day after birth the Ca2+-accumulating activity of the neonatal microsomes had increased, that of the rabbit via an increase in Ca2+ uptake and that of the guinea pig by an increase in Ca2+ binding. These changes were accompanied by an increase in the activity of the Ca2+-dependent ATPase. The results are interpreted to mean that the cardiac SR changes at about the time of birth, and that although the pattern of these changes may be species specific they result in an increase in the Ca2+-accumulating activity of the SR.
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