The effect of small hydrostatic pressure gradients on the rate of active sodium transport across isolated living frog-skin membranes.

1. The rate of active sodium transport across living isolated skins from Rana temporaria was measured when the skins were bulged inwards and outwards by small constant hydrostatic pressure gradients and by pushing them mechanically in the absence of such gradients. The effect of pressure gradients in the absence of bulging was also studied.2. An apparatus was designed to circulate Ringer solution to each side of the skin at constant temperature, flow and pressure. The pressures were controlled to within 0.5 mm H(2)O.3. It was found that bulging the skins in the absence of hydrostatic pressure gradients had no effect on sodium transport but that pressure gradients of less than 5 mm H(2)O had a marked effect, increasing transport when the pressure was higher on the outside of the skin, and decreasing it when the pressure was higher on the inside.4. It is concluded that increasing surface area does not influence sodium transport, whereas small hydrostatic pressure gradients have a marked effect.5. Possible causes for this phenomenon are discussed and its significance is considered with special reference to sodium reabsorption from the proximal tubule of the kidney.