Inhibition of Vacuolar Ion Channels by Polyamines

Abstract

In this work, direct effects of cytosolic polyamines on the two principle vacuolar ion channels were studied by means of patch-clamp technique. Fast and slow activating vacuolar channels were analyzed on membrane patches isolated from vacuoles of the red beet taproot. The potency of the fast and of the slow vacuolar channel blockage by polyamines decreased with a decrease of the polycation charge, spermine4+ > spermidine3+ > putrescine2+. In contrast to the inhibition of the fast vacuolar channel, the blockage of the slow vacuolar channel by polyamines displayed a pronounced voltage-dependence. Hence, in the presence of high concentration of polyamines the slow vacuolar channel was converted into a strong inward rectifier as evidenced by its unitary current-voltage characteristic. The blockage of the slow vacuolar channel by polyamines was relieved at a large depolarization, in line with the permeation of polyamines through this channel. The voltage-dependence of blockage was analyzed in terms of the conventional model, assuming a single binding site for polyamines within the channel pore. Taking advantage of a simple linear structure of naturally occurring polyamines, conclusions on a possible architecture of the slow vacuolar channel pore were drawn. The role of common polyamines in regulation of vacuolar ion transport was discussed.

Polyamines Improve K+/Na+ Homeostasis in Barley Seedlings by Regulating Root Ion Channel Activities

“…spermidine 31 putrescine 21). Similar to our results, previous studies also showed that polyamines blocked the slow-and fast-activating vacuolar cation channel in a charge-dependent manner Brü ggemann et al, 1998;Dobrovinskaya et al, 1999). These results suggested that polyamines may modulate ion channel activities through direct binding to the channel proteins.…”

“…9, B and C), suggesting the recirculation of K 1 from shoots to roots was decreased. Similar to our results, polyamines were well characterized as potent blockers of inward K 1 channels in both plant cells (Brü ggemann et al, 1998; Dobrovinskaya et al, 1999;Liu et al, 2000) and mammalian cells (Shin and Lu, 2005). Thus, by regulating inward and outward K 1 currents at different mode, spermidine prevented K 1 loss from shoots.…”

“…However, the involved mechanism remains unclear. Importantly, polyamines have been shown to be efficient inhibitors of both slow and fast vacuolar cation channels (Brü ggemann et al, 1998;Dobrovinskaya et al, 1999). In addition, polyamines also were characterized as potent blockers of inward K 1 currents across the plasma membrane of guard cells (Liu et al, 2000).…”

Reduced Tonoplast Fast-Activating and Slow-Activating Channel Activity Is Essential for Conferring Salinity Tolerance in a Facultative Halophyte, Quinoa

“…Thus, it appears that SV and FV currents make nearly equal contributions toward Na + flux across the tonoplast, and the total channelmediated current is fairly comparable to the current generated by the whole vacuolar population of H + pumps (Hedrich et al, 1988). However, as commented above, tonoplast channel activity is under the control of numerous second messengers and, as such, may be significantly up-or down-regulated in planta (Brüggemann et al, 1998;Carpaneto et al, 1999;Dobrovinskaya et al, 1999;Hedrich and Marten, 2011;Gutla et al, 2012). This may change the balance between the relative contribution of SV and FV channels toward tonoplast Na + fluxes under natural conditions.…”

Polyamines Interact with Hydroxyl Radicals in Activating Ca2+ and K+ Transport across the Root Epidermal Plasma Membranes

“…In animal cells, PAs block a variety of K + and other cation-selective channels (Drouin and Hermann, 1994;Ficker et al, 1994;Lopatin et al, 1994;Bähring et al, 1997;Lu and Ding, 1999). In plants, PAs inhibit PM Shaker-type K + channels in guard, cortical, epidermal, and xylem parenchyma cells (Liu et al, 2000;Zhao et al, 2007), nonselective cation channels in mesophyll and root PM Zhao et al, 2007), as well as nonselective cation fast and slow vacuolar channels (Brü ggemann et al, 1998;Dobrovinskaya et al, 1999aDobrovinskaya et al, , 1999b. PAs are the only organic polycations that are present in sufficient quantities under stress to play the role of channels blockers without compromising cell metabolism (Alcázar et al, 2010).…”