SLC4A11, a new addition to the SLC4 superfamily of bicarbonate transporters has not been thoroughly tested for possible HCO
3 − transport. Three different experiments were conducted to test possible Na
+-coupled HCO
3 − transport by SLC4A11 in BCECs transfected with
siSLC4A11.
Figure 6 shows that transfection with
siSLC4A11 in BCECs caused an approximately 70% decrease in SLC4A11 expression between 48- and 72-hour posttransfection. First, the effect of SLC4A11 knockdown on CO
2/HCO
3 −-induced changes in pH
i was determined.
Figure 7A shows that in control cells a typical CO
2/HCO
3 − response includes slight acidification due to CO
2 influx followed by alkalinization due to Na
+:HCO
3 − influx that is persistent in the presence of CO
2/HCO
3 −. Contribution of SLC4A11 to the net bicarbonate transport should be indicated by a decrease in the rate and amplitude of alkalinization in
siSLC4A11-transfected cells.
Figure 7B shows a response similar to control in
siSLC4A11-transfected cells.
Figures 7C,
7D summarize the rate and amplitude of alkalinization, respectively, indicating no significant difference due to SLC4A11 knockdown from control. Second, intracellular Na
+ concentrations were measured with a similar protocol to further assess Na
+:HCO
3 − transport. If SLC4A11 is a Na
+-dependent HCO
3 − transporter, then siSLC4A11 knockdown should reduce the rate of Na
+ influx in response to CO
2/HCO
3 −.
Figures 8A and
8B show representative [Na
+ i] traces from control and transfected cells, respectively.
Figure 8C summarizes the data from different trials and shows that the rate of Na
+ influx was not significantly different between the control and the transfected. Third, the effect of
siSLC4A11 knockdown on Na
+-free induced acidification in the presence of CO
2/HCO
3 − was measured. In
siSLC4A11-transfected cells the rate and amplitude of acidification and the rate of recovery should be reduced if SLC4A11 has Na
+-coupled HCO
3 − cotransport activity.
Figures 9A and
9B are representative pH
i traces from control and transfected cells.
Figures 9C and
9D summarize the results from different trials and indicate that the rate and amplitude of acidification and the rate of recovery in the presence of CO
2/HCO
3 − was not significantly different between control and transfected cells. In summary, these results indicate that SLC4A11 does not produce any measurable Na
+:HCO
3 − transport in BCECs.