Calculations used to determine allosteric effect of FGF-A homologues slowing intrinsic fast inactivation assuming modified LTI model
| | Onset | Recovery | Inferred | Expt. | Modified LTI prediction | Standard LTI prediction | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| τi (ms) | SSI | ki (/s) | klti (/s) | τf (ms) | τs (ms) | ki’ (/s) | τi’ (ms) | ki/ki’ | As | τi (ms) | As (LTI’) | τi (ms) | As (LTI) | τi (ms) | |
| NaV1.2 | 0.36 ± 0.09 | −62.4 | 2777.8 | | 8.7 ± 2.3 | | 2777.8 | 0.36 | | | 0.36 | | | | |
| +14A | 0.58 ± 0.12 | −48.2 | | | 5.4 ± 1.8 | 592.9 ± 111.5 | 724.6 | 1.38 | 3.83 | 0.60 | 0.58 | 0.60 | 0.55 | 0.28 | 0.26 |
| IQM+14A | 0.92 ± 0.24 | −44.4 | | 1087 | – | 565.5 ± 88.3 | | | | | | | | | |
| FGF14B | 0.64 ± 0.09 | −52.9 | | | 7.2 ± 2.0 | | 1562.5 | | 1.78 | | | | | | |
| +13A | 0.49 ± 0.10 | −49.0 | | | 6.3 ± 1.7 | 2017.6 ± 324.0 | 814.8 | 1.23 | 3.23 | 0.45 | 0.49 | 0.45 | 0.67 | 0.19 | 0.29 |
| IQM+13A | 1.50 ± 0.30 | −40.8 | | 666.7 | – | 1831.5 ± 383.5 | | | | | | | | | |
| +12A | 0.45 ± 0.06 | −51.8 | | | 5.0 ± 2.6 | 497.2 ± 97.7 | 1840.9 | 0.54 | 1.51 | 0.29 | 0.45 | 0.29 | 0.39 | 0.21 | 0.28 |
| IQM+12A | 1.33 ± 0.20 | −43.5 | | 751.9 | – | 565.4 ± 112.5 | | | | | | | | | |
| +11A | 0.52 ± 0.22 | −55.4 | | | 7.9 ± 2.7 | 173.1 ± 19.7 | 1446.3 | 0.69 | 1.92 | 0.44 | 0.52 | 0.44 | 0.39 | 0.29 | 0.26 |
| IQM±11A | 0.88 ± 0.16 | −43.8 | | 1136.4 | – | 155.8 ± 34.5 | | | | | | | | | |
| | Onset | Recovery | Inferred | Expt. | Modified LTI prediction | Standard LTI prediction | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| τi (ms) | SSI | τf (ms) | τs (ms) | τi’ (ms) | As | τi (ms) | As (LTI’) | τi (ms) | As (LTI) | τi (ms) | |||||
| NaV1.2 | 0.36 ± 0.09 | −62.4 | 2777.8 | | 8.7 ± 2.3 | | 2777.8 | 0.36 | | | 0.36 | | | | |
| +14A | 0.58 ± 0.12 | −48.2 | | | 5.4 ± 1.8 | 592.9 ± 111.5 | 724.6 | 1.38 | 3.83 | 0.60 | 0.58 | 0.60 | 0.55 | 0.28 | 0.26 |
| IQM+14A | 0.92 ± 0.24 | −44.4 | | 1087 | – | 565.5 ± 88.3 | | | | | | | | | |
| FGF14B | 0.64 ± 0.09 | −52.9 | | | 7.2 ± 2.0 | | 1562.5 | | 1.78 | | | | | | |
| +13A | 0.49 ± 0.10 | −49.0 | | | 6.3 ± 1.7 | 2017.6 ± 324.0 | 814.8 | 1.23 | 3.23 | 0.45 | 0.49 | 0.45 | 0.67 | 0.19 | 0.29 |
| IQM+13A | 1.50 ± 0.30 | −40.8 | | 666.7 | – | 1831.5 ± 383.5 | | | | | | | | | |
| +12A | 0.45 ± 0.06 | −51.8 | | | 5.0 ± 2.6 | 497.2 ± 97.7 | 1840.9 | 0.54 | 1.51 | 0.29 | 0.45 | 0.29 | 0.39 | 0.21 | 0.28 |
| IQM+12A | 1.33 ± 0.20 | −43.5 | | 751.9 | – | 565.4 ± 112.5 | | | | | | | | | |
| +11A | 0.52 ± 0.22 | −55.4 | | | 7.9 ± 2.7 | 173.1 ± 19.7 | 1446.3 | 0.69 | 1.92 | 0.44 | 0.52 | 0.44 | 0.39 | 0.29 | 0.26 |
| IQM±11A | 0.88 ± 0.16 | −43.8 | | 1136.4 | – | 155.8 ± 34.5 | | | | | | | | | |
To calculate the effective intrinsic fast inactivation rate, ki' when an FGF is associated with NaV1.2, we assume that this modification is unrelated to the onset or recovery from LTI, but arises from an interaction perhaps of the trefoil domain or other part of the FGF N-terminal with the NaV subunit mediating an allosteric effect on inactivation. This arises independent of the LTI inactivation domain.
Column 1: construct designation
Column 2–7: measured values reported above
Inferred rates and time constants for Allosteric LTI model.
Column 8: Calculated ki' from As = klti/(klti + ki'), rearranging yielding ki' = ki' (1-As)/As.
Column 9: τi = 1000/(ki' + klti), predicted inactivation tau in presence of FGF-A.
Column 10: fold-slowing of intrinsic fast inactivation rate.
Expt. values
Column 11: Measurements of As following single depolarization.
Column 12: Measured time constant of inactivation for NaV1.2+FGF-A homologue.
Values predicted from allosteric LTI model, based on calculation of ki' based on As
Column 13: As from LTI* model.
Column 14: τi based on LTI* model.
Values predicted from standard LTI model
Column 15: As from standard LTI model.
Column 16: τi based on standard LTI model.