Fluorescence combined with excised patch: measuring calcium currents in plant cation channels

Area of Science:

• Plant Cell Biology
• Ion Channel Physiology
• Biophysical Techniques

Background:

• Calcium ions (Ca2+) are crucial secondary messengers regulating numerous cellular processes.
• Understanding calcium transport mechanisms is vital for plant physiology.
• Conventional patch-clamp electrophysiology has limitations in directly measuring calcium fluxes.

Purpose of the Study:

• To introduce and validate the Fluorescence combined with Excised Patch (FLEP) technique.
• To investigate calcium permeation through the slow vacuolar (SV) channel.
• To demonstrate the advantages of FLEP over traditional methods for studying ion channels.

Main Methods:

• Utilized the excised patch configuration combined with fura-2 fluorescence detection (FLEP).
• Applied voltage stimulation to tonoplast patches and monitored fluorescence signals.
• Tested SV channel inhibitors and vacuoles from Arabidopsis tpc1 knockout mutants.

Main Results:

• Sustained fluorescence signals confirmed calcium permeation through the SV channel.
• SV channel inhibitors and tpc1 knockout abolished both SV currents and fluorescence.
• Fractional calcium currents were voltage-dependent, reaching ~10% of total SV currents at positive potentials.
• Simultaneous recording of calcium and potassium fluxes was achieved.

Conclusions:

• The FLEP technique provides a robust method for studying calcium fluxes through ion channels.
• FLEP overcomes limitations of conventional electrophysiology, enabling detection of simultaneous ion movements.
• This technique is valuable for investigating divalent ion-selective channels and transporters.