FUROSEMIDE - A SPECIFIC INHIBITOR OF P-I TRANSPORT ACROSS THE PLASMA-MEMBRANE OF PLANT-CELLS

A search was made for inhibitors of P-i uptake that act directly on th e P-i transporter in the plasma membranes of Catharanthus roseus cells to inhibit P-i uptake without inhibition of proton pumping. Using sta ndard electrodes, we monitored changes in pH and in the concentration of K+ ions, as well as the rate of P-i uptake, when an inhibitor to be tested was applied to the cells in unbuffered medium. A9C (28 mu M), a blocker of anion channels, inhibited P-i uptake but it also inhibite d the proton pump. However, a structurally similar inhibitor, furosemi de, inhibited P-i uptake without inhibiting proton pumping. It is sugg ested that the carboxylic group of these inhibitors interacts with the P-i-binding site (probably an amino group) of the P-i transporter in the plasma membrane and that the hydrophobic structure of these inhibi tors facilitates their accumulation in the plasma membrane.