An examination of the evidence for membrane pores in frog skin.

1. Measurements of the diffusional permeability, P(d), of tritiated water in isolated frog skin bathed in sulphate Ringer have been made under different stirring conditions.2. The mean +/- S.E. values for P(d) were found to be (6.5 +/- 0.3), (7.9 +/- 0.5), (9.7 +/- 0.7) and (11.1 +/- 0.8) x 10(-5) cm sec(-1) at 120, 300, 500 and 1000 rev/min. It is considered that these results indicate the existence of ;unstirred layers' associated with frog skin.3. The hydraulic conductivity, L(p), of the skin in sulphate Ringer was found to be (2.36 +/- 0.07) x 10(-7) cm sec(-1) atm(-1) (+/- S.E. of estimate), and no marked increase in this value for L(p) was found when the stirring rate was increased from 0 to 500 rev/min.4. It is considered that these results show that previous comparisons of the relative magnitudes of L(p)RT/V(w) (where V(w) is the partial molar volume of water) and P(d) for frog skin have been in error because of the presence of ;unstirred layers'.5. The bearing of our results and other evidence on the question of pores in cell membranes has been discussed.