Characterization of the High-Affinity Verapamil Binding Site in a Plant Plasma Membrane Ca2+-selective Channel |
| |
Authors: | M Piñeros M Tester |
| |
Institution: | (1) Department of Botany, University of Adelaide, S.A., Australia, AU;(2) Department of Plant Sciences, University of Cambridge, Downing St., Cambridge, CB2 3EA, UK, GB |
| |
Abstract: | Despite biochemical evidence for the existence of high-affinity phenylalkylamine receptors in higher plants, their effects
on channel activity have only been demonstrated at relatively high concentrations. We have performed a quantitative single-channel
analysis of the changes induced by extracellular verapamil in the rca channel a wheat root plasma membrane Ca2+-selective channel (Pi?eros & Tester, 1995. Planta
195:478–488)]. Concentrations as low as 0.5 μm verapamil induced a blockade of the inward current, with no evident reduction of the single-channel current amplitude. Blockade
by verapamil was concentration and voltage dependent. Preliminary analysis suggested the blockade was due to a reduction in
the maximum open state probability rather than a change in V0.5. Further analysis of the association and dissociation rate constants revealed a binding site located 56 to 59% down the voltage
drop from the extracellular face of the channel, with a K
d
(0) of 24 to 26 μm. This results in a K
d
at −100 mV of 2 μm. Methoxyverapamil had qualitatively the same effects. This intra-pore binding site can be accessed directly from the extracellular
side of the rca channel, but apparently not from the cytosolic side.
Received: 15 August 1996/Revised: 23 December 1996 |
| |
Keywords: | : Calcium channel — Methoxyverapamil — Verapamil — Wheat roots |
本文献已被 SpringerLink 等数据库收录! |
|