Isolation of a potassium-selective ion channel from the plasma membrane of the broad bean Vicia faba L.

Potassium ions are essential for plant nutrition and play an important role in osmoregulation and plant movement. Recent patch clamp investigations and molecular analysis have identified voltage-dependent potassium channels responsible for translocation of this ion across plant membranes. In order to characterize these transporters on the biochemical level, a potassium channel protein was isolated from Vicia faba under preservation of its functional integrity. Potassium channel activity was monitored by tracer flux and black lipid bilayer measurements. The capability for K+ transport copurified with a 67 kDa protein from V. faba plasma membranes. A monoclonal antibody directed against the 67 kDa protein blocked channel activity. Single channels with a unit conductance of 40 pS were highly selective for K+ over Na+.