Negative potential level in the outer layer of the toad skin

Abstract

The isolated skin of the toad Bufo marinus ictericus when impaled from the outer surface by glass microelectrodes filled with 3 M 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 mum. Null value is obtained at 19+/-3 mum, with positive values for deeper impalements. Indications of cell impalements (abrupt voltage and resistance jumps) were frequently observed at sites deeper than 25 mum 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 the stratum corneum. PDi measured at a depth of 5 mum 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 on PDi. Acidification of the external solution from pH 9 is accompanied by a reduction in the negative value of PDi. At pH 3 PDi 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 the stratum corneum. Differences in K and Cl mobilities, responsible for the origin of PDi, were attributed to fixed charges in the matrix of the stratum corneum, with density and polarity determined by their degree of proponation, controlled by the hydrogen ion concentration of the external solution. Skin potential, short-circuit current and their relationship to PDI were discussed.

Saturable K+ pathway across the outer border of frog skin (Rana temporaria): Kinetics and inhibition by Cs+ and other cations

“…Some authors found K § dependent diffusion potentials and short-circuit currents in normal epithelia [28,33], only with mucosal hypertonicity [-7] or after inhibition of the active Na § transport by ouabain [-21]. Conductance measurements revealed an increase of conductance with increasing [K] o [12,19], and a saturating K + conductance was even observed for the skin of Rana esculenta [19].…”

Permeability parameters of the toad isolatedstratum corneum

“…To account for this observation, they raised the possibility that the cornified layer could be missing in their preparations. The presence of fixed charges in the matrix of the stratum corneum, as suggested in a previous report [25], may also contribute through a Donnan exclusion [12] to alter the Na + activity at the external surface of the cells of the stratum granulosum, especially when the outside bathing solution is of low ionic concentration.…”

“…The role of the stratum corneum in electrophysiological experiments has been discussed by several authors. Thus, Whittembury [34], Rawlins et al [26] and Nunes with Lacaz Vieira [25] suggested that the resistance of the stratum corneum is negligible compared to the total electrical resistance of the epithelium. On the other hand, discrepancies were observed between resistances of the stratum corneum measured with single-and with double-barreled glass microelectrodes [25]; the values measured with double-barreled electrodes were much higher than those obtained with single-barreled electrodes.…”

“…Thus, Whittembury [34], Rawlins et al [26] and Nunes with Lacaz Vieira [25] suggested that the resistance of the stratum corneum is negligible compared to the total electrical resistance of the epithelium. On the other hand, discrepancies were observed between resistances of the stratum corneum measured with single-and with double-barreled glass microelectrodes [25]; the values measured with double-barreled electrodes were much higher than those obtained with single-barreled electrodes. Lindemann and Thorns [18], however, emphasize that in most epithelia investigated by them the main resistive barrier appeared to be at the outermost surface of the epithelium.…”

“…It was also our aim to test directly the existence of fixed charges in the matrix of the stratum corneum suggested by the results of earlier experiments [25]. These fixed charges were postulated to account for observations made in the super-ficial layer of the epithelium during alterations of the external bathing solution.…”