PATCH-CLAMP ANALYSIS OF THE DOMINANT PLASMA-MEMBRANE K-MEDIA L - ITS SIGNIFICANCE FOR THE P-STATE AND K-STATE( CHANNEL IN ROOT CELL PROTOPLASTS OF PLANTAGO)

Ion channels in the plasma membrane of root cell protoplasts of Planta go media L. were studied with the patch clamp technique in the cell-at tached patch and outside-out patch configuration. An outward rectifyin g potassium channel was dominantly present in the plasma membrane. It appears responsible for the diffusional part, dominated by the K+ diff usion potential, of the cell membrane potential, in vivo. This channel is activated at potentials near to and more positive than the K+ diff usion potential. The dependence of this ion channel on K+ activity and voltage has been characterized. The current-voltage relationships of the open channel at various K+ concentrations are described by a four- state model. The membrane potential of intact protoplasts appears eith er dominated by the K+ diffusion potential, the protoplast is then sai d to be in the K state, or by the pump potential generated by the plas ma membrane-bound proton pump/H+ ATPase, the P state. An experimental procedure is described to determine in cell-attached patch mode the st ate of the protoplast, either K or P state.