| Autor: |
Miedema, H, Prins, HBA, Staal, H. |
| Jazyk: |
angličtina |
| Rok vydání: |
1996 |
| Předmět: |
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| Zdroj: |
Journal of membrane biology, 152(2), 159-167. Springer Verlag |
| ISSN: |
0022-2631 |
| Popis: |
In vivo studies with leaf cells of aquatic plant species such as Elodea nuttallii revealed the proton permeability and conductance of the plasma membrane to be strongly pH dependent. The question was posed if similar pH dependent permeability changes also occur in isolated plasma membrane vesicles. Here we report the use of acridine orange to quantify passive proton fluxes. Right-side out vesicles were exposed to pH jumps. From the decay of the applied Delta pH the proton fluxes and proton permeability coefficients (P-H+) were calculated. As in the intact Elodea plasma membrane, the proton permeability of the vesicle membrane is pH sensitive, an effect of internal pH as well as external pH on P-H+ was observed. Under near symmetric conditions, i.e., zero electrical potential and zero Delta pH, P-H+ increased from 65 x 10(-8) at pH 8.5 to 10(-1) m/sec at pH II and the conductance from 13 x 10(-6) to 30 x 10(-4) S/m(2). At a constant pH(i) of 8 and a pH(o) going from 8.5 to 11, P-H+ increased more than tenfold from 2 to 26 x 10(-6) m/sec. The calculated values of P-H+ were several orders of magnitude lower than those obtained from studies on intact leaves. Apparently, in plasma membrane purified vesicles the transport system responsible for the observed high proton permeability in vivo is either (partly) inactive or lost during the procedure of vesicle preparation. The residue proton permeability is in agreement with values found for liposome or planar lipid bilayer membranes, suggesting that it reflects an intrinsic permeability of the phospholipid bilayer to protons. Possible implications of these findings for transport studies on similar vesicle systems are discussed. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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