Regulation of protein synthesis in lactating rat mammary tissue by cell volume.
The effect of changing cell volume on rat mammary protein synthesis has been examined. Cell swelling, induced by a hyposmotic challenge, markedly increased the incorporation of radiolabelled amino acids (leucine and methionine) into trichloroacetic acid (TCA)-precipitable material: reducing the osmolality by 47% increased leucine and methionine incorporation into mammary protein by 147 and 126% respectively. Conversely, cell shrinking, induced by a hyperosmotic shock, almost abolished the incorporation of radiolabelled amino acids into mammary protein: increasing the osmolality by 70% reduced leucine and methionine incorporation into mammary protein by 86 and 93% respectively. The effects of cell swelling and shrinking were fully reversible. Volume-sensitive mammary tissue protein synthesis was dependent upon the extent of the osmotic challenge. Isosmotic swelling of mammary tissue, using a buffer containing urea (160 mM), increased the incorporation of radiolabelled leucine into TCA-precipitable material by 106%. Swelling-induced mammary protein synthesis was dependent upon calcium: removing extracellular calcium together with the addition of EGTA markedly reduced volume-activated protein synthesis. Cell swelling-induced protein synthesis was inhibited by the Ca(2+) ATPase blocker thapsigargin suggesting that volume-sensitive protein synthesis is dependent upon luminal calcium.
Grant
A C
AC
Hannah Research Institute, Ayr, Scotland, UK.
Gow
I F
IF
Zammit
V A
VA
Shennan
D B
DB
D000818:Animals; D001940:Breast / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002364:Caseins / Q000096:biosynthesis; D048429:Cell Size / Q000187:drug effects; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007774:Lactation; D007930:Leucine / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D009994:Osmolar Concentration; D014176:Protein Biosynthesis; D051381:Rats; D017208:Rats, Wistar; D013462:Sulfur Radioisotopes; D019284:Thapsigargin / Q000494:pharmacology; D014238:Trichloroacetic Acid; D014316:Tritium
D002364:Caseins; D013462:Sulfur Radioisotopes; D014316:Tritium; D004533:Egtazic Acid; D014238:Trichloroacetic Acid; D019284:Thapsigargin; D008715:Methionine; D007930:Leucine; D002118:Calcium