Potassium channels in Eremosphaera viridis

Abstract

The dependence of the membrane potential of Eremosphaera viridis on different external concentrations of potassium, sodium, calcium, and protons was compared with the diffusion potential measured in the dark and in the presence of NaN3. In contrast to some other algae, the membrane potential in the light as well as in the dark seemed to be predominantly determined by the calculated diffusion potential and less by an electrogenic pump which, however, seemed to be involved at potassium concentrations >1 mol·m(-3) and at higher pHos (>pH 6). Furthermore, some characteristics of an action-potential-like response (CAP) triggered by light-off, and independent of the membrane-potential threshold value, were determined. The CAP had a delay period of 5.4 s and needed 4.5 s for polarization to a plateau. On average, the plateau held for 8.8 s and the CAP lasted 37.7 s. The peak amplitudes of CAP (P AP) exactly followed the Nernst potential of potassium. Other cations like sodium, calcium and protons did not appreciably affect the peak amplitudes of CAP. From these and other results it can be assumed that the CAP is caused by a temporary opening of potassium channels in the plasma membrane of Eremosphaera (Köhler et al., 1983, Planta 159, 165-171). The release of a CAP by light-off has been partly explained by the participation of a transient increase of proton concentration in the cytoplasm. It was possible to trigger a CAP by external pH changes and by the addition of sodium acetate, thus supporting the hypothesis that a pH decrease in the cytoplasm may be one element of the signal transfer from the photosynthetic system to the potassium channels in the plasmalemma. Calcium also seemed to have an influence on triggering the CAP.

Isolation of Protoplasts from the Coccal Green Alga Eremosphaera viridis De Bary for Patch‐clamp Measurements

“…The course of these transient currents could be subdivided into three phases: a fast activation phase, a short plateau phase and a slow inactivation phase. This corresponds to the course of transient potassium currents measured by Kohler et al (1986) in intact cells of Eremosphaera. Hence, we assume these inward currents to be caused by the activity of potassium channels responsible for the TP in this alga.…”

“…the socalled transient potential (TP). The properties of this TP have already been characterized by means of conventional electrophysiological methods (for summary see Kohler. 1990).…”

From damage response to action potentials: early evolution of neural and contractile modules in stem eukaryotes

“…Some cell-wide binary responses mediated by action potentials have been described in other protists—for example, the escape response of Stentor , Vorticella and Actinocoryne ( box 2 )—but they involve highly specialized mechanisms and are probably derived. Action potentials of unknown function have also been detected in the green algae Chara [ 173 ], Eremosphaera [ 174 , 175 ] and Acetabularia [ 51 ], and in the diatom Odontella [ 176 ].…”

Implications of Control Theory for Homeostasis and Phosphorylation of Transport Molecules*

“…This paper deals with a particular aspect of such a feed-back loop: the activation and deactivation ofthe transport molecule. The basic ideas of this approach are not restricted to homeostasis, because activation and deactivation of transport molecules becomes obvious in phenomena like excitation (Kohler et al, 1986), oscillations (Fisahn et al, 1986) or switching between open and closed states of channels as observed in patch clamp experiments (Sakmann and Neher, 1983;Bert1 et al, 1988).…”