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 < 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 I­II). Thus, decreased ATP hydrolysis only partially ex­plained the decreased Ca2⁺ uptake. In contrast, calculation of apparent Ca2⁺ pump coupling ratios (mol of Ca2⁺ trans-ported/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.