Rapid effect of light on the K+ channel in the plasmalemma ofNitella

Vanselow, K.; Hansen, Ulf‐Peter

doi:10.1007/bf01869472

Cited by 40 publications

(34 citation statements)

References 67 publications

(96 reference statements)

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“…The aim of the investigation of Plieth et al (1997) was to understand why some authors had found coupling between changes in pHc and pCac (Felle 1988) and others had not (Vanselow andHansen 1989, Miller andSanders 1989). Simultaneous measurement of the changes in fluorescence of BCEFC-dextran and Fura-dextran clearly demonstrated that the existence of this coupling depends on the difference between pH and pCa, which led to the insight that all authors were correct over the range of pH in which their experiments were conducted.…”

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confidence: 99%

Cytosolic Ca2+ and H+ buffers in green algae: A reply

Plieth

Hansen

1998

Protoplasma

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Summary: The explanation of the coupling between butyrateinduced changes in cytosolic pH and pCa by means of a H+/Ca 2+ exchange buffer as proposed by Plieth et al. [Protoplasma (1997) 198: 107-124; 199: 223] was questioned by Sch6nknecht and Bethmann [Protoplasma (1998) 203: 206-209]. They suggested an allosteric control of binding similar to the Hill equation. Fitting the measured pH-pCa coupling shows that a distinction between the models requires data which would be outside the experimentally accessible range. Plausibility considerations provide a support for the exchange buffer. The Hill equation is just a phenomenological approach which does not account for the diversity of allosteric mechanisms. The benefits of the exchanger model are firstly its mechanistic simplicity and secondly its flexibility as the same set of equations can also be used for an allosteric interaction between H +-and Ca 2+-binding sites. The model can easily be extended to include future more detailed data. Finally, the cytosolic buffer capacities for H + and Ca 2+ are discussed,

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confidence: 99%

Cytosolic Ca2+ and H+ buffers in green algae: A reply

Plieth

Hansen

1998

Protoplasma

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“…On the other hand, the light-modulated transport system in mesophyll cells induced a rapid depolarization, which was immediately followed by repolarization and a subsequent slower hyperpolarization (16,(27)(28)(29)(30)(31). The hyperpolarization seemed to be regulated by changes in activity of the plasma membrane H ϩ -ATPase and voltage-dependent ion channels (31)(32)(33). Analysis of metabolites in the presence of oligomycin, which blocked the F 1 F 0 -ATPase, revealed a dramatic decrease in the mitochondrial and cytosolic ATP concentration (34), indicating that mitochondria-driven ATP production was decreased.…”

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confidence: 99%

Mitochondria Provide the Main Source of Cytosolic ATP for Activation of Outward-rectifying K+ Channels in Mesophyll Protoplast of Chlorophyll-deficient Mutant Rice (OsCHLH) Seedlings

Goh

Jung

Roberts

et al. 2004

Journal of Biological Chemistry

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The role of mitochondria in providing intracellular ATP that controls the activity of plasma membrane outward-rectifying K ؉ channels was evaluated. The Os-CHLH rice mutant, which lacks chlorophyll in the thy- The OsCHLH mutant is unable to fix CO 2 and exhibits reduced growth. Wild type and mutant plants exhibit similar rates of respiratory O 2 uptake in the dark, whereas the rate of photosynthetic O 2 evolution by the mutant was negligible during illumination. During dark respiration the wild type and mutant exhibited similar levels of cytoplasmic ATP. In the mutant oligomycin treatment (an inhibitor of mitochondrial F 1 F 0 -ATPase) drastically reduced ATP production. The fact that this was reversed by the addition of glucose suggested that the mutant produced ATP exclusively from mitochondria but not from chloroplasts. In whole cell patch clamp experiments, the activity of outward-rectifying K ؉ channels of rice mesophyll cells showed ATPdependent currents, which were 1.5-fold greater in wild type than in mutant cells. Channels in both wild type and mutant cells were deactivated by the removal of cytosolic ATP, whereas in the presence of ATP the channels remained active. We conclude that mesophyll cells in the OsCHLH rice mutant derive ATP from mitochondrial respiration, and that this is critical for the normal function of plasma membrane outward-rectifying K ؉ channels.Mitochondrial metabolism not only impacts on other cellular biosynthetic and catabolic processes, but also plays an important role in providing the overall cellular energy supply. Dark respiration and photosynthesis are metabolic pathways that produce redox equivalents and ATP to meet the energy requirements to support cell growth and maintenance (2). The central role of mitochondria in plants is reflected by the array of mitochondrial transporters and shuttles that transfer metabolites and reducing equivalents back and forth between mitochondria and the cytosol. Oxidative phosphorylation provides the cytosol with ATP, which is required for sucrose synthesis and other cytosolic processes. Studies with specific respiratory inhibitors have shown that oxidative phosphorylation occurs both in darkness and in light (2-4). However, very little is known about the regulation of mitochondrial respiration in photosynthetic mesophyll cells, and the role of mitochondrial ATP production as a source of cytosolic ATP in this process is not fully understood.Many biochemical reactions in plant and mammalian cells depend on a tightly controlled ratio of ATP to ADP. In mammalian mitochondria, this ratio is preserved by regulatory mechanisms that couple the rate of cellular ATP consumption to the rate of ATP production by oxidative phosphorylation (5-8). Hence, efficient communication between cellular energy stores and membrane metabolic sensors is necessary for regulation of membrane excitability and associated functions. In most mammalian cells, there is a class of K ϩ channels whose activity is closely coupled to metabolism by ATP (9, 10). Recent studies have...

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“…Recent work examining light regulation of K+ transport has implicated regulation by photosynthesis (1,7,10,17 (18). In this species, there is K+ channel activation by either high external Ca2" or A23 187 (15).…”

Section: Discussionmentioning

confidence: 99%

“…Besides phytochrome, K+ channel activity could also be regulated by photosynthesis, as indicated in Elodea, where K+ uptake is activated by light and inhibited by DCMU (10), in Nitella, where there is a temporal correlation between Chl fluorescence and K+ conductance (17), in Riccia, where lightinduced DCMU-inhibited acidification of the cytoplasm is followed by an increase in cytoplasmic K+ (for which the effect of DCMU was not determined) (1), and in Eremosphaera, where either a transition to dark or DCMU stimulates K+ conductance (7). Therefore, photosynthesis could also regulate K+ channel activity in Mougeotia.…”

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confidence: 99%