Negative potential level in the outer layer of the toad skin
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- Nunes, M.A. & Lacaz Vieira, F. J. Membrain Biol. (1975) 24: 161. doi:10.1007/BF01868621
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The isolated skin of the toadBufo marinus ictericus when impaled from the outer surface by glass microelectrodes filled with 3m KCl shows a voltage profile which is a continuous function of the depth of impalement. The superficial intraepithelial potential difference measured with reference to the external solution (PDi) is negative with NaCl-Ringer's solution on both sides of the skin, displaying a minimum of −26.7±3.6 mV at 6±2 μm. Null value is obtained at 19±3 μm, with positive values for deeper impalements. Indications of cell impalements (abrupt voltage and resistance jumps) were frequently observed at sites deeper than 25 μm from the outer surface. Measurements of the electrical resistance between the microelectrode and the external solution, made with single- and double-barreled microelectrodes, showed great discrepancies, which may be attributed to distinct pathways of different resistances in thestratum corneum. PDi measured at a depth of 5 μm was a logarithmic function of Na2SO4 or K2SO4 concentration in the external solution, increasing in negativity with a reduction in concentration. Substitution of Na by K in the external solution had only minor effects onPDi. Acidification of the external solution from pH 9 is accompanied by a reduction in the negative value ofPDi. At pH 3PDi was positive.PDi was interpreted as a diffusion potential at the tip of the microelectrode due to KCl diffusion from the electrode into the matrix of thestratum corneum. Differences in K and Cl mobilities, responsible for the origin ofPDi, were attributed to fixed charges in the matrix of thestratum corneum, with density and polarity determined by their degree of protonation, controlled by the hydrogen ion concentration of the external solution. Skin potential, short-circuit current and their relationship toPDi were discussed.