Abstract
Uptake of cystine and factors affecting the transport were investigated in adult rat hepatocytes in primary monolayer culture. The cystine uptake was initially mediated by Na+-dependent route(s). However, the activity of Na+-dependent uptake decreased markedly during the culture, and Na+-independent uptake emerged with a lag period of 12 h in response to insulin and dexamethasone in the culture medium. After 48 h in culture, cystine was mainly transported into the cells through this Na+-independent route. The action of insulin and dexamethasone on the enhancement of the Na+-independent uptake was apparently additive, and the enhancement was completely blocked by cycloheximide or actinomycin D. Emergence of the Na+-independent uptake of cystine was also regulated by cell density; at lower density, the uptake tended to be elevated. The transport of cystine through the Na+-independent system was pH sensitive and was inhibited by some anionic amino acids, such as glutamate and homocysteate, but not by aspartate. These results suggest that the emerging system is similar to the ones reported in fibroblasts and in some hepatoma cell lines; the anionic form of cystine is transported through the system.
Highlights
Na+-independent uptake emerged with a lag period of 12 h in response to insulin and dexamethasone in the culture medium
The transport of cystine through the Na+-independent system was pH sensitive and was inhibited by some anionic amino acids, such as glutamate and homocysteate, but notby aspartate. These results suggest that the emerging systemis similar to the onreesported in fibroblasts and in some hepatoma celllines;the anionic form of cystineis transported through the system
We have investigated which transport system with prewarmed phosphate-buffered saline, transport was initiated is responsible for cystine uptake, especially whether a Na+- by addition of 0.5ml of uptake medium containing labeled amino independent system similar to the one described in human acid (1 pCi/0.5 ml)
Summary
From the Division of Biochemistry, Tsukuba University School of Medicine, Sakura-mura, Ibaraki 305, Japan. Characteristics of various or absence of insulin and dexamethasone in the culture medium after transport systems for neutral [7,8,9,10,11,12], anionic [13],and cationic [14]amino acids are studied in isolated rat hepatocytes in suspension or in primary culture. We have investigated which transport system with prewarmed phosphate-buffered saline, transport was initiated is responsible for cystine uptake, especially whether a Na+- by addition of 0.5ml of uptake medium containing labeled amino independent system similar to the one described in human acid (1 pCi/0.5 ml).
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