Characterization of the High-Affinity Verapamil Binding Site in a Plant Plasma Membrane Ca2+-selective Channel

Characterization of the High-Affinity Verapamil Binding Site in a Plant Plasma Membrane... 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 (Piñeros & 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. The Journal of Membrane Biology Springer Journals

Characterization of the High-Affinity Verapamil Binding Site in a Plant Plasma Membrane Ca2+-selective Channel

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Copyright © Inc. by 1997 Springer-Verlag New York
Life Sciences; Biochemistry, general; Human Physiology
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