Regulation of Tonoplast K+ Channels by Voltage in the Range of Physiological Electric Potentials

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Abstract
The presence of tonoplast ion channels regulated by voltage in the physiological range of transtonoplast electric potential was studied in isolated vacuoles from Acer pseudoplatanus cultured cells. In symmetrical KCl or K-gluconate depolarizing pulses induced instantaneously developing, decaying outward currents, while in symmetrical tetramethylammonium chloride these currents were absent. The outward currents were reduced if the depolarizations were applied from a holding potential of +30 millivolts and increased upon depolarizations from a holding potential of −30 millivolts and even more from a holding potential of −50 millivolts. These results indicate that the outward currents are due to K+ movement through channels which are open around 0 millivolt and close at positive potentials. These K+ channels, regulated in the range of the physiological electric potentials reported for the vacuoles in situ, are likely the same K+ channels activated by hyperpolarizations which we have previously described (R Colombo, R Cerana, P Lado, A Peres [1988] J Membr Biol 103: 227-236).