The effect of external pH on the membrane potential of Nitella and its linkage to metabolism

The membrane potential of Nitella is highly sensitive to externalpH in the neutral region (pH 5.5 to 8) in the light. We foundthat the sensitivity usually was reduced by darkness, metabolicinhibitors (DCMU, DNP) or cooling. Under some circumstancesthe high pH-sensitivity of the membrane potential was observedeven in the dark. However, even in this case, it was reducedby DNP or cooling. These results indicate that the externalpH-dependence of the membrane potential of Nitella is closelylinked to metabolism. (Received May 8, 1973; )     

The electrogenic ion pump revealed by the external pH effect on the membrane potential of Nitella. Influences of external ions and electric current on the pH effect

The influences of external ions and electric current on thepH effect of the membrane potential of Nitella are described.Results are explained in terms of a pH-dependent electrogenicion pump. The reduction of membrane resistance with a pH rise is attributedto the pump current being potential-dependent. (Received July 9, 1974; )     

The effect of metabolites on the pH gradient and membrane potential of the bean peribacteroid membrane

The effects of malate, succinate, and glutamate on the kinetics of changes in the pH gradient (delta pH) and membrane potential (delta psi) on the peribacteroid membrane (PBM) of the symbiosomes of bean root nodules varying in age were recorded spectrophotometrically. Addition of all the tested metabolites to potassium-free incubation medium stimulated a passive acidification of the peribacteroid space (PBS) and dissipation of delta psi in PBM of young developing nodules in the presence of the K+/H+ antiporter nigericin in the medium. However, in mature nodules with a high nitrogen-fixing activity, only malate and succinate (but not glutamate) increased delta pH during both passive and ATP-dependent PBS acidification. Dicarboxylates also caused dissipation of both delta pH in the presence of nigericin in the medium and delta psi generated on PBM by H+-ATPase. A decrease in the effects of metabolites on delta pH and the absent activity of the PBM H+ pump were observed in the aging nodules. The obtained data on the changes in deltapH and dlta psi caused by the metabolites in question suggest that PBM is permeable for all these metabolites only in young nodules. Only malate and succinate (but not glutamate) are transported through PBM in mature nodules; and the rate of metabolite translocation through PBM in aging nodules is decreased.     

The effect of metabolites on the pH gradient and membrane potential of the bean peribacteroid membrane

The effects of malate, succinate, and glutamate on the kinetics of changes in the pH gradient (ΔpH) and membrane potential (Δψ) on the peribacteroid membrane (PBM) of the symbiosomes of bean root nodules varying in age were recorded spectrophotometrically. Addition of all the tested metabolites to potassium-free incubation medium stimulated a passive acidification of the peribacteroid space (PBS) and dissipation of ΔpH in PBM of young developing nodules in the presence of the K⁺/H⁺ antiporter nigericin in the medium. However, in mature nodules with a high nitrogen-fixing activity, only malate and succinate (but not glutamate) increased ΔpH during both passive and ATP-dependent PBS acidification. Dicarboxylates also caused dissipation of both ΔpH in the presence of nigericin in the medium and Δψ generated on PBM by H⁺-ATPase. A decrease in the effects of metabolites on ΔpH and the absent activity of the PBM H⁺ pump were observed in the aging nodules. The obtained data on the changes in ΔpH and Δψ caused by the metabolites in question suggest that PBM is permeable for all these metabolites only in young nodules. Only malate and succinate (but not glutamate) are transported through PBM in mature nodules; and the rate of metabolite translocation through PBM in aging nodules is decreased.     

The effects of bicarbonate ions and external pH on the membrane potential and resistance ofNitella translucens

Summary The effects of bicarbonate ions on the membrane potential and resistance ofNitella translucens are shown to be primarily due to the change in pH produced by the bicarbonate acting as a buffer, and not due to the presence of an electrogenic anion pump. The mechanism by which pH affects the membrane potential is discussed in the context of recent work by other authors on this effect.     

Resting membrane potential and action potential of Nitella expansa protoplasts

Inside negative membrane potentials were observed for protoplastsobtained from Nitella expansa leaf internodal cells in mediacontaining 1 to 100 mM CaCl₂ using the microelectrode technique.The potential values were less negative than the membrane potentialof intact N. expansa leaf internodal cells. In addition, anaction potential consisting of two components—a fast componentand a slow component—was induced by electrical stimulationfor the protoplasts as well as the intact cells. (Received December 18, 1979; )     

Rhythmic change of membrane potential and cyclosis of Nitella internode

The membrane potential of Nitella internode shows a spontaneousrhythmicity. The period depends largely upon temperature andthe length of the cell. Moreover, the period is reversibly prolongedat low temperature and also by treatment with cytochalasin B.We concluded that this bioelectrical rhythm is closely relatedto cytoplasmic streaming. (Received August 11, 1975; )     

Light-induced hyperpolarization of membrane potential in Nitella flexilis call plasmalemma

Light-induced hyperpolarization of the membrane potential in Nitella flexilis cell plasmalemma was investigated by the clamping method. It is shown that this response is of an excitation character. The equivalent electric diagram used in the work and the electromotive force included on its basis allowed consideration of two possible (from the common point of view) mechanisms of the response: the action of the electrogenic ion pump and membrane specific permeability to a definite ion. The membrane being in the hyperpolarization state is not capable of acting as a bicarbonate electrode. It is suggested that the response under study is defined by the action of the electrogenic pump, the role of which is performed by HCO2(3)-dependent H+-ATPase with the ion channel as an exciting one.     

Nitella fluctuation and instability in the membrane potential near threshold.

Excitation of Nitella internodal cell was investigated as an example of the phase transition in an open system far more thermal equilibrium. The power density spectrum of the membrane potential fluctuation had a bulge in a frequency range lower than 1 Hz at the resting state and a peak at approximately 0.03 Hz at a depolarized state near the threshold. A critical oscillation in the membrane potential was observed when threshold was gradually approached from the resting state. Repetitive firing was observed under a step-current of the superthreshold value. The frequency of spectral peaking, critical oscillation, and repetitive firing agree well with each other. The result suggests that the hard-mode instability occurs in the Nitella internodal cell. The membrane impedance had no peak in the same frequency region as the peak of the voltage spectrum. The spectral peak may be ascribed to be electrogenic pump modulated by the metabolic feedback system in photosynthesis.     

The internal pH and membrane potential of the insulin-secretory granule

1. Incubation of isolated hepatocytes with fructose at concentrations above 3 mM resulted in an apparent inhibition of pyruvate kinase assayed in crude extracts at sub-optimal phosphoenolpyruvate concentrations. 2. Fructose at concentrations below 3 mM caused an activation of the enzyme. 3. Increases in the hepatocyte contents of the positive effectors fructose 1.6-bisphosphate and fructose 1-phosphate were found at all concentrations of fructose up to 10mM. 4. Removal of the extrahepatocyte medium from the hepatocytes by washing resulted in an activation of the enzyme at all concentrations of fructose examined. 5. Inhibitors of the enzyme were shown to accumulate in the hepatocytes despite the depletion of ATP (a known negative effector) caused by higher concentrations of fructose. Indeed the inhibition of pyruvate kinase appeared to be correlated to the depletion of ATP. 6. Alanine (a known inhibitor) was shown to accumulate in hepatocytes as a consequence of incubation with fructose. 7. Allantoin and uric acid were shown to be inhibitors of a partially purified pyruvate kinase preparation assayed both in the presence and in the absence of fructose 1.6-bisphosphate. 8. Allantoin, but not uric acid, accumulated in the extrahepatocyte medium as a result of incubation of the cells with 10 mM-fructose.     

Dependence of the membrane potential of Chara cells on external pH in the presence or absence of internal adenosinetriphosphate

The dependence of the membrane potential (E_m) and the membrane resistance (R_m) of Chara australis R. Brown on the pH of the external medium (pH₀) was studied by controlling the activity of the plasmamembrane H⁺ pump under both light and dark conditions. The activity of the pump was controlled by regulating the internal ATP or Mg²⁺ concentration in tonoplast-free cells prepared by vacuolar perfusion. In these cells, which contained Mg · ATP (mgATP cells), E_m and R_m were very sensitive to pH₀, as in normal cells. E_m was more negative in light than in the dark at all pH₀ values tested. Tonoplast-free cells with very low [ATP]_i (-ATP cells) or [Mg²⁺]_i (-Mg cells) showed very weak dependence of E_m and R_m on pH₀. Thus, the active and not the passive component of E_m was sensitive to pH₀. At the same time, the high permeability of the plasma membrane to H⁺ was questioned. In both-ATP cells and-Mg cells, E_m was scarcely affected and R_m markedly decreased on illumination.Abbreviations CyDTA 1,2-cyclohexanediamine-N,N-tetraacetic acid - EGTA ethyleneglycol-bis-(-aminoethylether)N,N-tetraacetic acid - HK hexokinase     

The effect of cell excision and microelectrode perforation on membrane resistance measurements of Nitella translucens.

The effect of cell excision and microelectrode perforation on the membrane resistance measurements of Nitella translucens was determined by direct experiment. From the results it is concluded that perforation has no effect on cells as short as 1 cm. Current leakage though the node of an excised cell has however to be given some consideration. The method used for determining the resistance recovery to insertion has a wide application and its simplicity will encourage its use in other biological systems.