Table 3.
Parameters used in the modified Fraser & Huang (2004) model
| Parameter | Symbol | Value | Refs. (see legend) |
|---|---|---|---|
| Membrane NH4+ permeability | PNH4 | 2.8 × 10−9 cm s−1 | 1 |
| Membrane NH3 permeability | PNH3 | 1.0 × 10−5 cm s−1 | 2 |
| Membrane H+ permeability | PH | 4.0 × 10−5 cm s−1 | 3 |
| Membrane H2O permeability | PH2O | 1.56 × 10−4 cm s−1 | 4 |
| (Thus, ratio PK: PNH4: PNH3: PH: PH2O) | 1: 0.07:250: 1000: 3,900 | ||
| Relative NHE 'permeability' | PNHE | 50 000 | 5 |
| Equilibrium constant of buffer A | pKa(A) | 6.03 | 6 |
| Equilibrium constant of buffer B | pKa(B) | 7.57 | 7 |
See Fraser & Huang (2004) for other basic parameters. The parameters used here reflect normal physiological values for amphibian skeletal muscle, except for PNHE which was chosen to give pHi= 7.25 under control conditions. 1Derived from present experimental data given PK= 4 × 10−8 cm s−1 (Adrian, 1956); 2Boron & De Weer (1976); 3Decoursey (2003); 4Frigeri et al. (2004); 5chosen to give pHi= 7.25 under baseline conditions; 6, 7Leem et al. (1999).