An examination of the evidence for membrane pores in frog skin

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Abstract
Measurements of the diffusional permeability, Pd, of tritiated water in isolated frog skin bathed in sulfate Ringer have been made under different stirring conditions. The mean +S.E. values for Pd were found to be (6.5[plus or minus]0.3), (7.9[plus or minus]O.5), (9.7[plus or minus]0.7) and (11.1[plus or minus]0.8) x 10-5 cm sec-1 at 120, 300, 500 and 1000 rev./mlh. It is considered that these results indicate the existence of "unstirred layers" associated with frog skin. The hydraulic conductivity, Lp, of the skin in sulfate Ringer was found to be (2.36[plus or minus]0.07)x10-7cm sec-1 atm-1([plus or minus]S.E. of estimate), and no marked increase in this value for Lp was found when the stirring rate was increased from 0 to 500 rev.fmin. E is considered that these results show that previous comparisons of the relative magnitudes of LpRT/[image]w (where [image]w is the partial molar volume of water) and Pd for frog skin have been in error because of the presence of "unstirred layers". The bearing of our results and other evidence on the question of pores in cell membranes have been discussed.