ELECTRIC EXCITATION OF VACUOLE JUST WITHI N THE PROTOPLAST ISOLATED FROM THE CELL OF HIGHER-PLANT

Macroscopic transient currents with the millisecond kinetics resemblin g the current responses of electroexciting membranes uder the voltage damp conditions were registered by the loose patch clamp method (LPC) in protoplasts isolated from cells of higher plants in a high-potassiu m medium (130 mM). The detected currents had high threshold of activat ion (400 mV) and were activated only when positive (but not negative) voltage pulse was fixed at a glass micropipette tip, They displayed re fractority in response to the positive voltage pulse. Specific blocker s of the plasmalemma ion channels produced no effect on these currents . The transient currents were not registered when the plasmalemma surf ace was not pulled into a micropipette. The absence of artefacts due t o the loosy contact has been demonstrated, Using the combination of LP C and the current clamp methods, the curves of voltage alteration in t he cytoplasm acid vacuole during the development of the descovered cur rents were obtained. The criteria of the cytoplasmic and vacuolar loca tion of the microelectrode tip for the current clamp method were preli minarily determined, The phenomenological analysis suggested the vacuo lar origin of the detected currents thereby undicating the existence o f the phenomenon of vacuole electric excitation in protoplasts (in sit u) isolated from cell of higher plants, The induction of the vacuole e xcitation in the protoplast occurs by the LPC principle and then the l ocal excitation has been generalized on the whole tonoplast. In this c ase, the high values of the excitation threshold voltage is converted by a systems of dividers into the threshold of vacuole excitation, and plasmalemma ''keeps silence'' during the application of a shot pulse of the voltage set. The potassium nature of the inward vacuolar curren ts is supposed, A possible physiological significance of the discovere d effects is discussed.