DIRECTIONAL DIFFERENCES IN THE PERMEABILITY TO WATER OF THE ISOLATED URINARY BLADDER OF THE TOAD, BUFO MARINUS

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Abstract
SUMMARY: 1. If the osmotic gradient is favourable vasopressin increases the rate of water movement across the bladder of the toad from the serosal to the epithelial side, which is the opposite direction to that seen physiologically. 2. Water transfer down an osmotic gradient is 1·8 times more rapid towards the serosal than towards the epithelial side. Vasopressin increases this difference so that water is moving 4·9 times as rapidly to the serosal side. Iodoacetate reduces this effect of vasopressin. 3. If water is moving down an osmotic gradient towards the anode, a higher electric current increases the water movement in the presence, but not in the absence, of vasopressin. If water movement is taking place towards the cathode an increased current has no effect. 4. With vasopressin present, absence of sodium on the epithelial side of the bladder reduces water transfer down an osmotic gradient towards the serosal side, but has no effect on water movement down an osmotic gradient in the opposite direction.