Sarcolemmae from Chicken Skeletal Muscle. 2. Properties

Abstract

SUMMARY– Sarcolemmae are usually identified solely by morphological characteristics. We have determined several chemical and enzymic properties of sarcolemmae from chicken breast muscle prepared by homogenization of aged muscle in dilute CaCl2 solution, washing 4 times in NaCl‐histidine at pH 7.4, extraction with water buffered to pH 7 and isolation by differential centrifugation on a discontinuous sucrose gradient. The phospholipid content of the sarcolemmae was low, representing only 2 to 3% by weight compared with the 20 to 35% usually found in membraneous systems. This discrepancy may be due to the relatively small proportion of plasma membrane in the sarcolemma.Analyses indicate little contamination by nuclei or mitochondria. The sarcolemmae have, like the microsomal fraction, high contents of RNA and glucose‐6‐phosphatase activity. The sarcolemma is either rich in these elements or is contaminated by other subcellular elements, such as the transverse tubules (T system), which are. The sarcolemmae display a Mg+2‐ activated ATPase activity which is typical for membraneous systems. Lactate dehydrogenase was shown to be associated with the sarcolemmae. Whether this represents the situation in vivo or is an artifact of preparation is not clear. The sarcolemmae are capable of binding soluble LDH.

Isolation and some properties of rabbit skeletal muscle cell membranes

“…The complex structure of the sarcolemma observed in the electron micro scope illustrates why much confusion has arisen concerning definition of the "sarcolemma". In the present study, the term "sarcolemma" was 127 used to designate the limiting, 75-100 X plasmaleinna investing the skeletal muscle fiber (Fawcett and Selby, 1958;Bennett, 1960) rather than the more complex three-layer structure, _i.^., the plasmalemma, basement membrane, and fibrous connective tissue layers, often designated as the sarcolemma (Kono and Colowick, 1961;Koketsu e_t al., 1964 ;Mauro and Adams, 1961;Hultin and Westort, 1969b). Since all preparations made by the low ionic strength procedure described in the present study contained the fibrous connective tissue and basement membrane layers in addition to the plasmalemma, it is obvious that one limitation of the low ionic strength procedure described in this study is its inability to remove the outer two connective tissue and basement membrane layers.…”