K-CL- COTRANSPORT AND VOLUME REGULATION IN THE LIGHT AND THE DENSE FRACTION OF HIGH-K+ DOG RED-BLOOD-CELLS()

We examined a chloride (Cl-)-dependent K+ transport (K+-Cl- cotranspor t) and regulatory volume decrease in dog red blood cells with high K+, low Na+, and high glutathione (GSH) content (HK/HG) due to the presen ce of an Na+-K+ pump. The HK/HG cells were separated according to thei r density, and the age-marker enzyme activities, such as glucose-6-pho sphate dehydrogenase and cholinesterase, were determined. Unexpectedly , we found that young cells were heavier (more dense) and smaller in s ize compared with the old cells, which were lighter (less dense) and l arger. The K+-Cl- cotransport was nearly 10-fold higher in the most de nse cells, representing a 12% fraction of the total population compare d with the lightest cohort. Although K+-Cl- cotransport in both the de nse and the light cells was activated by N-ethylmaleimide, swelling an d depletion of cellular divalent cations and the activation of the tra nsport in the dense cells was greater. Both the dense and light cells regulated their volume when they were isosmotically swollen. Therefore , the lower activity of K+-Cl- cotransport might not explain the relat ive large volume in old HK/HG cells. The concentration of GSH and glut amate was higher in the light cells. Thus the higher the GSH and gluta mate concentration, the greater the cell volume and the lower the K+-C l- cotransport.