A function that relates protein synthetic rates to potassium activity in vivo

A newly developed experimental system allows the controlled alteration of intracellular K + activity (a K ) and the measurement of amino acid incorporation rates in a single cell, the Xenopus oocyte. We found that as a K is increased by microinjecting a K + salt, [ 3 H]leucine incorporation (R) varies over a 100‐fold range, first stimulated and then inhibited as it passes through four response regions (A–D). In region A (a K ∼ 60–100 mM), R is at a nongrowth or maintenance level and is stimulated weakly by increasing a K . In region B (a K ∼ 100–130 mM), R is stimulated intensely by increasing a K , roughly tripling with every 10 mM increase. In region C (a K ∼ 130–160 mM), R is inhibited intensely by increasing a K . Finally, in region D (a K > 160 mM), R is inhibited weakly as a K increases. Collectively, the four response regions constitute the oocyte's R/a K response function. The function provides a comprehensive description of how K + activity influences the rate of protein synthesis in an intact cell. In the subsequent discussion, we compared the oocyte response function with the K + response determined in cell‐free translational systems. While in vivo and in vitro functions are similar, differences exist that may be important in a cellular control system. We then considered the relevance of the oocyte R/a K response function to “normal” processes in the oocyte and in somatic cells, i.e., those in which a K is varied by physiological changes in the plasma membrane. We concluded that the intensely stimulatory region B is importantly involved in hormonal action and other growth‐activating processes and that the entire R/a K response function may play a role in control of protein synthesis during the cell cycle.