A Perspective on the Slow Vacuolar Channel in Vacuoles from Higher Plant Cells

Historically, the vacuole has been an important system for the application of the patch-clamp technique to plant cells, and not only for reasons of simple preparation and the purity of its membrane. The vacuole is an intracellular organelle that can occupy up to 90% of the cellular volume of mature plant cells. For the plant cell, the tonoplast represents an essential crossing point between the cytosol and the vacuolar lumen containing a variety of transport systems. 1 Not only do these allow the storage of ions, metabolites, and xenobiotics, they also contribute to the homeostasis of cytosolic parameters, since the homeostasis of a given ion can be maintained by its release or uptake across the vacuolar membrane. In addition, the vacuole is likely to be involved in cellular signal transduction and can be an excellent model system for the study of calcium release from internal stores, leading to increases in cytosolic calcium. It is clear that the regulation of these processes is based on the permeability properties of the vacuolar membrane. Since its initial characterization, 2 the slowly activating vacuolar (SV) channel has been found in all tissue and plant species investigated so far. The SV channel represents the dominating conductance of the tonoplast at elevated cytosolic calcium concentrations. Interestingly, hypotheses about its physiological role have taken into consideration all the vacuolar functions mentioned above. Recent experimental evidence3 from Arabidopsis thalianastrongly indicates that the structure of the SV channel is determined by the TPC1 gene (two-pore channel 1). This work will briefly summarize the principal characteristics of this channel, concentrating on recent findings and otherwise by referring to previous reviews. 4-7

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