Membrane Chara

Fig. 6.23 Single-channel currents flowing across the membrane between the protoplast and vacuole of Chara corallina. Among several channels with different conductivity the recordings of the 130 pS channel are recorded here. The zero line is at the top of each curve. (By courtesy of F. Homble)...

Pesacreta TC, Lucas WJ. Plasma membrane coat and a coated vesicle-associated reticulum of membranes Their structure and possible interrelationship in Chara corallina. J Cell Biol 1984 98 1537-1545. 

Consider a solute having a permeability coefficient of 1CT6 ms-1 for the plasma membrane of a cylindrical Chara cell that is 100 mm long and 1 mm in diameter. Assume that its concentration remains essentially uniform within the cell. 

Equation 3.6, the Nernst equation, is an equilibrium statement showing how the internal and the external activities of ionic species / are related to the electrical potential difference across a membrane (Fig. 3-2). At equilibrium, a 10-fold difference in the activity of a monovalent ion across some membrane is energetically equivalent to and can balance a 59-mV difference in electrical potential (at 25°C). Hence, a relatively small electrical potential difference can energetically balance a large difference in activity or concentration across a membrane. For instance, if the external activity were 1% of the internal activity (aj/ax- = 0.01), the Nernst potential would be -118 mV for K+ and +118 mV for Cl- (Fig. 3-2). For some calculations, y° /y) is set equal to 1 (a less stringent assumption than setting both y° and yj equal to 1). Under this condition, a°fct- in Equation 3.6 becomes the ratio of the concentrations, c°/cj (a = yff Eq. 2.5). Such a substitution may be justified when the ionic strengths on the two sides of a membrane are approximately the same, but it can lead to errors when the outside solution is much more dilute than the internal one, as occurs for Chara or Nitella in pond water. 

McCool B, Xomeritakis G, Lin YS. Composition control and hydrogen permeation chara-teristics of sputter deposited palladium-silver membranes. J Memb Sci. 1999 161 67-76. Moss TS, Peachey NM, Snow RC, Dye RC. Multilayer metal membranes for hydrogen separation. Int J Hydrogen Energy. 1998 23(2) 99. 

Because of the diflBculties of separating the hydrophobic proteins of the inner membrane by gel electrophoresis, studies were more successful in which the product of mitochondrial protein synthesis was charae-terized using specific inhibitors. As a result the activity of a few mitochondrial enzymes seems to be linked to the function of the mitochondrial genome, or at least to the function of mitoribosomes. 

Some Techniques for Investigation of Electrochemical and Ion Transport Properties of Biological Cell Membranes The Case of Chara Corallina... 

SOME TECHNIQUES FOR INVESTIGATION OF ELECTROCHEMICAL AND ION TRANSPORT PROPERTIES OF BIOLOGICAL CELL MEMBRANES THE CASE OF CHARA CORALLINA... 

The experimental material which is used in this article consists of membranes of the isolated internodal cells of the freshwater green plants Characeae and mainly of Chara corallina. The cytoplasmic ion concentration of these cells can be determined directly because of their size. These giant cylindrical cells of corallina have a regular size, a diameter of about 0.7 to 1.2 mm and a length which can reach 20 cm. These cells easily survive after being isolated from the mother plant. The cell is composed... 

Figure 3. pH Dependence of the rest membrane potential of Chara cells... 

Figure 12 displays the response of the membrane potential to inward current pulses of different magnitudes. At low current density a purely passive response is observed. At 0.25 A and above, a spontaneous increase in voltage occurs which is followed by a slight voltage decrease in which large fluctuations can be observed. These results are similar to those observed on intact cells of Chara corallina , Nitella and on... 

Figure 12. Time-dependence response of the membrane potential of protoplasmic droplets of Chara clamped at different values of the current density. The values to the right of each curve indicates the magnitude of the current density in A.m 2 (from Reference 48).

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