同时测定小麦原生质体的电流与离子流，发现电流与K+密切相关，与Ca2+无关

关键词：微电极离子流测定 ( Microelectrode Ion-Flux Estimation); 膜片钳（Patch clamp）

参考文献：Matthew G. et al. The Plant Journal. 2006, 46:134-144

全文下载：http://www3.interscience.wiley.com/cgi-bin/fulltext/118565019/HTMLSTART

Simultaneous flux and current measurement from single plant protoplasts reveals a strong link between K⁺ fluxes and current, but no link between Ca²⁺ fluxes and current

Matthew Gilliham ^1,2*, Wendy Sullivan ² , Mark Tester ^3,4 and Stephen D. Tyerman ²

  ¹ Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK,
  ² School of Agriculture and Wine, Plant Research Centre, University of Adelaide, Waite Campus, PMB 1, Glen Osmond, SA 5064, Australia,
  ³ Australian Centre for Plant Functional Genomics, PMB 1, Glen Osmond, SA 5064, Australia, and
  ⁴ School of Agriculture and Wine, University of Adelaide, Australia

Correspondence to   *(fax +44 (0)1223 333953; e-mail mg253@cantab.net).

Copyright 2006 The Authors Journal compilation 2006 Blackwell Publishing Ltd

KEYWORDS

non-invasive self-referencing microelectrode ion-flux measurement • ion-selective electrodes • Microelectrode Ion-Flux Estimation • patch clamp electrophysiology • ion channels • selectivity

ABSTRACT

We present a thorough calibration and verification of a combined non-invasive self-referencing microelectrode-based ion-flux measurement and whole-cell patch clamp system as a novel and powerful tool for the study of ion transport. The system is shown to be capable of revealing the movement of multiple ions across the plasma membrane of a single protoplast at multiple voltages and in complex physiologically relevant solutions. Wheat root protoplasts are patch clamped in the whole-cell configuration and current–voltage relations obtained whilst monitoring net K⁺ and Ca²⁺ flux adjacent to the membrane with ion-selective electrodes. At each voltage, net ion flux (nmol m⁻² sec⁻¹) is converted to an equivalent current density (mA m⁻²) taking into account geometry and electrode efficiency, and compared with the net current density measured with the patch clamp system. Using this technique, it is demonstrated that the K⁺-permeable outwardly rectifying conductance (KORC) is responsible for net outward K⁺ movement across the plasma membrane [1:1 flux-to-current ratio (1.21 ± 0.14 SEM, n = 15)]. Variation in the K⁺ flux-to-current ratio among single protoplasts suggests a heterogeneous distribution of KORC channels on the membrane surface. As a demonstration of the power of the technique we show that despite a significant Ca²⁺ permeability being associated with KORC (analysis of tail current reversal potentials), there is no correlation between Ca²⁺ flux and KORC activity. A very significant observation is that large Ca²⁺ fluxes are electrically silent and probably tightly coupled to compensatory charge movements. This analysis demonstrates that it is mandatory to measure flux and currents simultaneously to investigate properly Ca²⁺ transport mechanisms and selectivity of ion channels in general.