Inhibition of the bicarbonate exit step in urinary acidification by a disulfonic stilbene.
Acidification of the luminal solution by the isolated turtle bladder involves H(+) secretion by a pump at the luminal membrane. The OH(-) dissociated in this process reacts with CO(2) and forms HCO(3) (-) which moves passively out of the cell across the serosal cell membrane. In the present study, this exit step for HCO(3) (-) was inhibited by serosal addition of the disulfonic stilbene, SITS, an agent which is thought to bind to a transport protein at the serosal cell membrane. 90 min after serosal addition of 0.5 mM SITS, H(+) secretion decreased by &gt; 80%. In contrast, luminal addition of SITS had no effect. During inhibition of H(+) secretion by serosal SITS, overall cell pH, measured by the 5, 5-dimethyl-2, 3-oxazolidinedione method, increased from 7.48+/-0.03 to 7.61+/-0.02. This increase of 0.13+/-0.02 pH U was associated with a much larger regional pH increase as judged from the decrement in the attainable pH gradient across the epithelium. After serosal SITS, this gradient was reduced from 2.88+/-0.06 to 2.09+/-0.11 pH U. In the absence of evidence for increased H(+) permeability or a change in the force of the H(+) pump, the gradient decrement of 0.79+/-0.08 U reflects a similar pH increment on the cytoplasmic side of the pump.SITS inhibits the exit of bicarbonate across the serosal cell membrane and, thereby, creates a compartment of high alkalinity in series with the pump. The increased electrochemical gradient across the active transport pathway is the primary factor in the inhibition of urinary acidification.
Inhibition of the bicarbonate exit step in urinary acidification by a disulfonic stilbene. Acidification of the luminal solution by the isolated turtle bladder involves H(+) secretion by a pump at the luminal membrane. The OH(-) dissociated in this process reacts with CO(2) and forms HCO(3) (-) which moves passively out of the cell across the serosal cell membrane. In the present study, this exit step for HCO(3) (-) was inhibited by serosal addition of the disulfonic stilbene, SITS, an agent which is thought to bind to a transport protein at the serosal cell membrane. 90 min after serosal addition of 0.5 mM SITS, H(+) secretion decreased by &gt; 80%. In contrast, luminal addition of SITS had no effect. During inhibition of H(+) secretion by serosal SITS, overall cell pH, measured by the 5, 5-dimethyl-2, 3-oxazolidinedione method, increased from 7.48+/-0.03 to 7.61+/-0.02. This increase of 0.13+/-0.02 pH U was associated with a much larger regional pH increase as judged from the decrement in the attainable pH gradient across the epithelium. After serosal SITS, this gradient was reduced from 2.88+/-0.06 to 2.09+/-0.11 pH U. In the absence of evidence for increased H(+) permeability or a change in the force of the H(+) pump, the gradient decrement of 0.79+/-0.08 U reflects a similar pH increment on the cytoplasmic side of the pump.SITS inhibits the exit of bicarbonate across the serosal cell membrane and, thereby, creates a compartment of high alkalinity in series with the pump. The increased electrochemical gradient across the active transport pathway is the primary factor in the inhibition of urinary acidification.