Maturation of calcium transport in cardiac sarcoplasmic reticulum.

Developmental changes in myocardial function have been described by a number of investigators. To further define the cellular basis for these changes, the present study was designed to characterize age-related changes in Ca2+ transport in sarcoplasmic reticulum (SR) vesicles isolated from six groups of sheep: group (Sp) I (100-105 days gestation), Gp II (128-132 days gestation), Gp III (postnatal, 0-3 days), Gp IV (4 wk), Gp V (8 wk), and Gp VI (maternal sheep). The maximal Ca2+ uptake for vesicles isolated from Gp I-V was significantly (p less than 0.01) decreased as compared to that measured for Gp VI (maternal) vesicles. However, Ca2+-dependent ATP hydrolysis was decreased only in the fetal SR vesicles (Gp I-II). Thus, decreased ATP hydrolysis only partially explained the decreased Ca2+ uptake. In contrast, calculation of apparent Ca2+ pump coupling ratios (mol of Ca2+ transported/mol of ATP hydrolyzed) showed that there was a marked increase in the coupling of Ca2+ transport to ATP hydrolysis during maturation of the heart. Inasmuch as the contractile state of the heart depends on precise regulation of Ca2+ concentration by the SR, these age-related changes in SR function may contribute to developmental changes in myocardial function.