K+ currents through SV-type vacuolar channels are sensitive to elevated luminal sodium levels
Article first published online: 25 JAN 2005
The Plant Journal
Volume 41, Issue 4, pages 606–614, February 2005
How to Cite
Ivashikina, N. and Hedrich, R. (2005), K+ currents through SV-type vacuolar channels are sensitive to elevated luminal sodium levels. The Plant Journal, 41: 606–614. doi: 10.1111/j.1365-313X.2004.02324.x
- Issue published online: 25 JAN 2005
- Article first published online: 25 JAN 2005
- Received 1 October 2004; revised 22 November 2004; accepted 25 November 2004.
- cell culture;
- SV channel;
- salt stress
Non-selective slow vacuolar (SV) channels mediate uptake of K+ and Na+ into vacuolar compartment. Under salt stress plant cells accumulate Na+ in the vacuole and release vacuolar K+ into the cytoplasm. It is, however, unclear how plants mediate transport of K+ from the vacuole without concomitant efflux of toxic Na+. Here we show by patch-clamp studies on isolated Arabidopsis thaliana cell culture vacuoles that SV channels do not mediate Na+ release from the vacuole as luminal Na+ blocks this channel. Gating of the SV channel is dependent on the K+ gradient across the vacuolar membrane. Under symmetrical K+ concentrations on both sides of the vacuolar membrane, SV channels mediate potassium uptake. When cytoplasmic K+ decreases, SV channels allow K+ release from the vacuole. In contrast to potassium, Na+ can be taken up by SV channels, but not released even in the presence of a 150-fold gradient (lumen to cytoplasm). Accumulation of Na+ in the vacuole shifts the activation potential of SV channels to more positive voltages and prevents gradient-driven efflux of K+. Similar to sodium, under physiological conditions, vacuolar Ca2+ is not released from vacuoles via SV channels. We suggest that a major Arabidopsis SV channel is equipped with a positively charged intrinsic gate located at the luminal side, which prevents release of Na+ and Ca2+, but permits efflux of K+. This property of the SV channel guarantees that K+ can shuttle across the vacuolar membrane while maintaining Na+ and Ca2+ stored in this organelle.