Table 5.
Binding Affinities and Functional Activities of the CCK/Opioid Peptides at the CCK-1 and CCK-2 Receptors
| Binding Affinity, [125I]CCK-8(SO3)b | PI assay | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Peptidea | hCCK-1c | hCCK-2c | hCCK-1d | hCCK-2d | ||||||
| LogIC50e | Ki/nMf | LogIC50e | Ki/nMf | LogEC50g | EC50/nM | Emaxh | LogEC50g | EC50/nM | Emaxh | |
| 1 | 32,000 | nc | nr | -- | nr | -- | ||||
| 2 | 2,500 | 4,900 | nr | -- | nr | -- | ||||
| 3 | >10,000 | >10,000 | nr | -- | nr | -- | ||||
| 4 | nc | nc | nr | -- | 5500 | -- | ||||
| 5 | 2,300 | >10,00 | ns | -- | 16,000 | 3.8 | ||||
| 6 | nc | nc | nr | -- | nr | -- | ||||
| RSA504 | 11.2 | 16 | 2540 | 15 | 1930 | 10.1 | ||||
| CK8 (SO3) | n.d. | - | n.d. | - | −7.55±0.15 | 28 | 59±3.0 | −7.57±0.24 | 27 | 16±1. |
Refer to Table 1 for the structure of the peptides.
Kd = 1.9 ± 0.2 nM for hCCK-1; Kd = 1.3 ± 0.4 nM for hCCK-2.
Carried out using whole cell lysate preparations from transfected HEK 293 cells that constitutively expressed the respective receptor type.
Carried out on hCCK-1 or hCCK-2 expressing cells cultured in 24 well titer plates.
Logarithmic values determined from the non-linear regression analysis of data collected from at least 2 independent experiments.
Anti-logarthmic value of the respective IC50.
Logarithmic values determined from the non-linear regression analysis of data collected from at least 2 independent experiments. The EC50 value is converted from the respective log EC50.
Saturable, maximum level of [3H]inositol phosphates produced in the cells upon incubation with the peptide, expressed as a ratio ± standard error of the amount of [3H]inositol phosphates produced in the presence of peptide over the basal level of [3H]inositol phosphates in untreated cells. n.c. incomplete competition of the radioligand at the highest test concentration of the peptide. An IC50 value cannot be determined. n.s. non-saturable dose-response curve. In these cases, stimulation of [3H]phosphotidylinositol hydrolysis was observed only at the highest test dose(s) of the peptide (1 ×10−5 and 1 ×10−4 M). An EC50 or Emax value cannot be determined. n.r. no stimulatory (or inhibitory) response at the highest test concentration of the peptide. n.d. not determined.