The action potential in Chara: Ca2+ release from internal stores visualized by Mn2+-induced quenching of fura-dextran
✍ Scribed by Christoph Plieth; Burkhard Sattelmacher; Ulf-Peter Hansen; Gerhard Thiel
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 502 KB
- Volume
- 13
- Category
- Article
- ISSN
- 0960-7412
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✦ Synopsis
Summary
The action potential (AP) in Chara is associated with a transient elevation in the concentration of cytoplasmic‐free Ca^2+^ ([Ca^2+^]~cyt~). The quenching properties of the fluorescent Ca^2+^ indicator dye fura‐dextran, in combination with Mn^2+^, was used to investigate whether this [Ca^2+^]~cyt~ transient is due to Ca^2+^ release from internal stores or to Ca^2+^ influx across the plasma membrane. Adding Mn^2+^ to the external medium or pre‐injection of Mn^2+^ into the vacuole caused no perceivable quenching of the fura fluorescence, during an AP. This makes it unlikely that Ca^2+^ influx across the plasma membrane or the tonoplast contributes significantly to the [Ca^2+^]~cyt~ transient in an excited cell. When cells were pre‐incubated in external solutions containing Mn^2+^ from 25 to 30 mM APs evoked a transient quenching of fura fluorescence in Mn^2+^‐free solutions. Under these conditions, the quenching must be attributed to an AP‐associated release of Mn^2+^ from internal stores. Based on the finding that exposing cells to millimolar concentrations of Mn^2+^ caused a progressive quenching of the fura fluorescence in non‐excited cells, it can be assumed that some Mn^2+^ enters the cells during pre‐incubation and is loaded into internal stores. During excitation, this stored Mn^2+^ is released together with Ca^2+^.