Depolarization-Activated K+ Channel in Chara Droplets

Abstract

A novel potassium channel was characterized in the droplet membrane of Cham gymnophylla. This channel has a conductance of about 90 pS (in symmetrical 0.15 M KCI), which is lower compared to the 170-pS K+ channel predominant in this preparation. In contrast to the large conductance K+ channel, the novel channel opened with a delay at depolarization and closed at hyperpolarization and did not require cytosolic Caz+ for its opening. It also showed comparatively weak selectivity for K+ over other monovalent cations, although its cation to anion selectivity was high. Externally or internally applied Cs+ blocked the channel in a voltage-dependent manner, similarly to the 170-pS channel. The sensitivity of the 90-pS channel to external tetraethylammonium chloride (half-blocking concentration approximately 1.5 mM) was 20-fold higher compared to the large conductance channel. With respect to its voltage-gating kinetics, the 90-pS channel was identified as a "slow delayed rectifier."

Mechanisms underlying turgor regulation in the estuarine alga Vaucheria erythrospora (Xanthophyceae) exposed to hyperosmotic shock

“…An efflux of −10 nmol m −2 s −1 was observed over 30 min after administering the shock. This type of leakage of K + out of the cell due to exposure to high external NaCl has been well documented in higher plants and also has been reported in Chara (Pottosin & Andjus ; Shabala et al . ; Bose et al .…”

“…2a,b). An efflux of −10 nmol m −2 s −1 was observed over 30 min after administering the shock.This type of leakage of K + out of the cell due to exposure to high external NaCl has been well documented in higher plants and also has been reported in Chara (Pottosin & Andjus 1994;Shabala et al 2005a;Bose et al 2013;Jayakannan et al 2013). Na + entry into the cell through NSCCs is thought to cause this, leading to a depolarization of Em (Shabala et al 2006).…”

Rapid reactions of spruce cells to elicitors released from the ectomycorrhizal fungus Hebeloma crustuliniforme, and inactivation of these elicitors by extracellular spruce cell enzymes

“…Therefore, one possible mechanism involved :in the primary events at the plasma membrane might be a depolarisation of the membrane caused by the elicitor-triggered C1-efflux. As a result depolarisation-activated K + and Ca 2 + channels might be opened, as was shown for Chara gymnophylla (Pottosin and Andjus 1994), Plantago media (Vogelzang and Prins 1994) and wheat roots (Huang et al 1994).…”

Multi-Scale Characean Experimental System: From Electrophysiology of Membrane Transporters to Cell-to-Cell Connectivity, Cytoplasmic Streaming and Auxin Metabolism

“…Another type of K + channel with smaller conductance (∼90 pS) was also observed in tonoplast droplets ( Tyerman and Findlay, 1989 ; Pottosin and Andjus, 1994 ). Pottosin and Andjus (1994) patch-clamped droplets of C. gymnophylla and classified these channels as slow delayed rectifier, activated by depolarization, not high Ca 2+ and blocked by TEA, and Cs + . The authors suggested a role for repolarization after excitation event.…”