Changes in the Structure, Composition and Function of Sarcoplasmic-Reticulum Membrane during Development

Abstract

The structure, chemical composition and function of the microsomal fraction, isolated by differential centrifugation and purified on sucrose gradients, from muscle of fetal, newborn and young rabbits were characterized and compared with those of sarcoplasmic reticulum vesicles from adult muscle. Negative staining shows that the microsomal vesicles isolated from muscles of embryos and newborn animals are smooth, in contrast to vesicles obtained from adult muscle which contain 4‐nm particles on their surface. The particles appear first in the microsomal vesicles from muscles of 5–8‐day‐old rabbits. Their number increases with the age of the animals. Ca2+‐pump protein, with molecular weight about 100000, accounts for 10% of the total protein content in sarcoplasmic reticulum membrane, isolated at the earliest stages of development analysed. Its amount increases continuously with the rabbit's age to the adult value of about 70% of total sarcoplasmic reticulum protein. The low amount of 100000‐dalton protein and lack of 4‐nm surface particles in sarcoplasmic reticulum vesicles obtained from fetal and newborn rabbits are strictly correlated with the low activity of Ca2+‐dependent ATPase and the ability to take up Ca2+. These activities rise in parallel with the age of the rabbits. On the other hand, Mg2+‐dependent ATPase activity is very high at the early stages of development and declines continuously to a low value in sarcoplasmic reticulum from adult muscle. The sarcoplasmic reticulum membrane from fetal and newborn rabbits contains a higher amount of lipids as compared with the membrane present in the muscle of adult animals. The ratio of both phospholipid to protein and neutral lipid to protein decreases with the age of the rabbits. The composition of sarcoplasmic reticulum phospholipid also changes during development.

Mechanism of Ca2+Transport by Sarcoplasmic Reticulum

“…Corresponding changes in the density of 40-A surface particles were observed after negative staining with K phosphotungstate [ Table 7; (376,508)]. …”

“…The evolution of the highly specialized SR with its characteristic protein and phospholipid composition from the phospholipid-rich primitive endoplasmic reticulum involves regulation of protein and phospholipid biosynthesis at several levels. The process was extensively studied in vivo (23,(45)(46)(47)97,376,382,395,396,(507)(508)(509), in tissue culture (182,217,261,262,327,345,417,683), and in cell-free translation systems (82,179,428,663).…”

Correlation between ultrastructural and functional changes in sarcoplasmic reticulum during chronic stimulation of fast muscle

“…The present analyses reveal a correlation between these biochemical and ultrastructural changes, and therefore support the concept that the intramembranous particles represent the structural equivalent of the Ca 2 + transport ATPase molecule or an oligomer of it within the membrane. Studies during ontogenesis of muscle in various mammalian species demonstrated a similar correlation between ffmctional and ultrastructural properties of SR (Baskin, 1974;Tillack etal., 1974;Sarzala, Pilarska, Zubrzycka & Michalak, 1975). An increase in the density of intramembranous particles of concave fracturing faces was accompanied by increases in ATPase activity, Ca 2+ transport, phosphoprotein formation and in phospholipid content (Baskin, 1974;Tillack et al, 1974).…”

ATPase Activities, Ca2+ Transport and Phosphoprotein Formation in Sarcoplasmic Reticulum Subfractions of Fast and Slow Rabbit Muscles

“…Probably Ca2+ sequestration by low density vesicles of the sarcoplasmic reticulum is supported in slow-twitch fibres by the mitochondria [42] or, as may be speculated, also by the sarcolemmal membrane. According to findings of Holland and Perry [41] and Sarzala et al [43] sarcoplasmic reticulum of embryonic muscle resembles in many respects the low density vesicles of the sarcoplasmic reticulum of slow-twitch muscle. This is true also for the ultrastructural appearance of sarcoplasmic reticulum from embryonic and immature muscle [43] which resembles the smooth-surfaced and tadpole-shaped vesicles of the low density fractions in Fig.…”