Table 1.
Effect of N-Terminal Truncations of Sodium-Hydrogen Exchanger 3 Stimulatory Peptide 1 on Sodium-Hydrogen Exchanger 3 Activity in Human Duodenal Enteroids
| N3SP-1 variant | Stimulation of NHE3 activity (%) | EC50 |
|---|---|---|
| N3SP-1 | Yes (38) | 152 nmol/L |
| N3SP-1Δ18 | No | |
| CP-2 (N3SP-1Δ10) | No | |
| N3SP-1Δ9 | No | |
| N3SP-1Δ8 | Yes (9) | 356 μmol/L |
| N3SP-1Δ7 | Yes (39) | 156 nmol/L |
| N3SP-1Δ6 | Yes (40) | 151 nmol/L |
| N3SP-1Δ5 | Yes (39) | 154 nmol/L |
NOTE. Concentration-dependent effects on NHE3 basal activity was determined using BCECF-fluorometry. Kinetic analysis was determined of extent of stimulation of basal NHE3 activity; analysis was by use of Hill equation. Truncation of 5, 6, or 7 N-terminal aa did not significantly alter the magnitude of the stimulation of NHE3 or alter the EC50; however, truncation of 8 aa reduced the stimulatory effect and significantly increased the EC50, whereas further truncations of 9, 10, and 18 aa produced peptides that were without effect on basal NHE3 activity.