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THE POLARIZATION CAPACITY AND RESISTANCE OF VALONIA : I. ALTERNATING CURRENT MEASUREMENTS

Blinks, L. R.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 20/03/1936 EN
Relevância na Pesquisa
15.94%
Alternating current measurements of the effective capacity and resistance of Valonia cells were undertaken to determine whether a static or polarization capacity was responsible for the large slow time curves of counter E.M.F. produced by the flow of direct current. (For this purpose it was necessary that the cells be in the regular state.) With external contacts at the ends of ceils, a large fall of impedance occurs over the frequency range from zero to 20,000 cycles, above which the impedance is low and essentially that of the cell interior. As a first approximation to the cell circuit, a simple series-parallel circuit was employed in the bridge balance, with a resistance setting to represent the cell wall (and protoplasmic leakage), shunting the protoplasmic capacity in series with a resistance (sap plus polarization resistance). Both the capacity and its associated series resistance fall off regularly with frequency, giving curved lines on logarithmic plots against frequency, the slope of the resistance plot being steeper, and approaching that of f–1, although curved to it. These parallel roughly the behavior of a polarizing electrode, which is also shown. Before concluding that the cell's capacity is therefore due to polarization...

PERMEABLE JUNCTIONAL COMPLEXES : The Movement of Lanthanum across Rabbit Gallbladder and Intestine

Machen, Terry E.; Erlij, David; Wooding, F. B. P.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/08/1972 EN
Relevância na Pesquisa
15.94%
Ionic lanthanum has been used to study transepithelial ion permeation in in vitro rabbit gallbladder and intestine (ileum) by adding 1 mM La3+ to only the mucosal bathing solution. Transepithelial fluid transport electrical potential differences (p.d.), and resistances were measured. During La3+ treatment the gallbladder's rate of active solute-coupled fluid transport remained constant, the resistance increased, and the 2:1 NaCl diffusion p.d. decreased. Mucosa-to-serosa fluxes of 140La3+ were measured and indicate a finite permeability of the gallbladder to La3+. La3+ also increased the transepithelial resistance and p d. of ileum. Electron microscopic examination of La3+-treated gallbladder showed: (a) good preservation of the fine structure, (b) electron-opaque lanthanum precipitates in almost every lateral intercellular space, most frequently near the apical end of the lateral spaces close to or within the junctional complex, (c) lanthanum among the subjacent muscle and connective tissue layers, and (d) lanthanum filling almost the entire length of so-called "tight" junctions. No observations were made which unequivocally showed the penetration of lanthanum into the gallbladder cells. Electron micrographs of similar La3+-treated ilea showed lanthanum deposits penetrating the junctional complexes. These results coupled with other physiological studies indicate that the low resistance pathway for transepithelial ion permeation in gallbladder and ileum is through the tight junctions A division of salt-transporting epithelia into two main groups...