Transient, specific and extremely rapid release of osmolytes from growing cells of Escherichia coli K-12 exposed to hypoosmotic shock.

The influence of hypoosmotic shock on the solute content of growing Escherichia coli K-12 cells was investigated at 37 degrees C. Within 20 s after the shock the cells had released most of their osmolytes K+, glutamate and trehalose. This release was specific and not due to rupture of the cell membrane, since under these conditions i) the cells neither lost protein nor ATP, ii) [14C]-labeled sucrose did not enter the cytoplasm from the periplasm, and iii) except for their glutamate and aspartate level, which decreased, the amino acid pool of alanine, lysine and arginine of the cells remained approximately constant. Within a minute after the shock the cells started to reaccumulate parts of their previously released glutamate, aspartate and K+, but not trehalose and resumed growth within 10 min after the shock. Experiments with K(+)-transport mutants showed that none of the genetically-identified K+ transport systems is involved in the K(+)-release process. Reaccumulation of K+ took place via the uptake systems TrkG and TrkH. The possibility is discussed that the exit of solutes after hypoosmotic shock occurs via several stretch-activated channels, which each allow the release of a specific osmolyte.