title: Developmental changes in myocardial mechanical function and subcellular organelles.
abstract: This study investigates the developmental changes in myocardial mechanical function and the function of subcellular organelles. Mechanical function was determined at various Ca2+ concentrations ( [Ca2+]0) in the isolated, arterially perfused heart of the fetus (28th day of gestation), newborn (3-5 day old), and adult rabbit. Maximal force of contraction in the fetus (observed at 7.5 mM [Ca2+]0) was significantly less than that in the newborn (observed at 30 mM ( [Ca2+]0), and both the fetus and newborn values were significantly less than that in the adult (observed at 15 mM [Ca2+]0). The myofibrillar content in the fetus and ATPase activity in the fetus and newborn were significantly less than in the adult at pCa 4 and 5 where this enzyme was maximally activated. Both the amount of sarcoplasmic reticulum (SR) and SR Ca2+ uptake per gram of muscle increased with age. Mitochondrial Ca2+ uptake was not observed at pCa more than 6 (physiological range) in all age groups. At pCa less than 6, mitochondrial Ca2+ uptake (per g muscle) in the newborn was significantly greater than in the fetus and adult. Ca2+ uptake by crude homogenate in the newborn was also greater than in the fetus and adult. These data suggest that the age-related change in myocardial contractility is due to the differences in intracellular Ca2+ concentration and myofibrillar content as well as ATPase activity. Intracellular Ca2+ concentration may vary with development depending on the relative capability of Ca2+-releasing system and Ca2+-sequestering system.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D005260:Female; D006321:Heart / Q000254:growth & development / Q000502:physiology*; D007811:Lanthanum / Q000494:pharmacology; D009206:Myocardium / Q000648:ultrastructure*; D011247:Pregnancy; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013347:Subcellular Fractions / Q000502:physiology; D013696:Temperature
chemical_list: D007811:Lanthanum; D000251:Adenosine Triphosphatases; D002118:Calcium