Fig. 5.

p_f does not depend on the driving force. An increase of the osmotic gradient from 0.1 to 1.5 M urea (from dark to light gray) resulted in an increased Mg²⁺ dilution close to the membrane, allowing determination of P_f. (Inset) From G measured simultaneously, the number of open channels and thus the single-channel hydraulic conductivity were calculated. p_f was constant over the interval of applied osmotic pressure.