DYRK1A Is a Regulator of S-Phase Entry in Hepatic Progenitor Cells

Plant cells contain two major pools of K+, one in the vacuole and one in the cytosol. The behavior of K+ concentrations in these pools is fundamental to understand-ing the way this nutrient affects plantigrowth. Triple-barreled microelectrodes have been used to obtain the first fully quantitative measurements of the changes in K+ activity (ay) in the vacuole and cytosol of barley (Hordeum vulgare L.) root cells grown in different K+ concentrations. The electrodes incorporate a pH-selective barrel allowing each measurement to be assigned to either the cytosol or vacuole. The measure-ments revealed that vacuolar aK declined linearly with de-creases in tissue K+ concentration, whereas cytosolic aK initially remained constant in both epidermal and cortical cells but then declined at different rates in each cell type. An unexpected finding was that cytoplasmic pH declined in parallel with cytosolic aK, but acidification of the cytosol with butyrate did not reveal any short-term link between these two parameters. These measurements show the very different responses of the vacuolar and cytosolic K+ pools to changes in K+ availability and also show that cytosolic K+ homeostasis differs quantitatively in different cell types. The data have