The H+/CI' Symporter in Root-Hair Cells of Sinapis alba'

In root-hair cells of Sinapis alba, cytosolic pH, cytosolic [Cl-1, membrane potential, and membrane resistance have been measured to investigate proton-driven CItransport across the plasma membrane. Rapid lowering of the external pH transiently increased cytosolic [Cl-] and acidified the cytoplasm. To an abrupt increase in external [Cl-] the cells reacted with a rapid initial depolarization and a subsequent slower hyperpolarization, which was accompanied by an increase in cytosolic [CI-] and [H*]. These results are indicative of an nH+/CIsymport with n > 1. Simultaneous recording of the membrane potential, the proton motive force, cytosolic pH, and cytosolic [Cl-] reveals that kinetically this CItransport depends on the pH gradient across the plasma membrane rather than on the membrane potential.