Estimated total ammonia concentrations in plasma and cutaneous (skin)intracellular fluid (ICF) required to maintain favorable NH3partial pressure gradients to the cutaneous surface of air-exposed mangrove killifish (Rivulus marmoratus) volatilizing NH3 in air at 25°C
| . | pH . | pK′† . | Total ammonia (μmol l–1) . | PNH3 (μ Torr) . |
|---|---|---|---|---|
| Cutaneous surface* | 7.84 | 9.18 | 1.03 | 1200 |
| Plasma‡ | 7.69 | 9.30 | 1.90 | 1200 |
| Cutaneous ICF§ | 7.1–7.4 | 9.34 | 4.0–7.9 | 1200 |
| . | pH . | pK′† . | Total ammonia (μmol l–1) . | PNH3 (μ Torr) . |
|---|---|---|---|---|
| Cutaneous surface* | 7.84 | 9.18 | 1.03 | 1200 |
| Plasma‡ | 7.69 | 9.30 | 1.90 | 1200 |
| Cutaneous ICF§ | 7.1–7.4 | 9.34 | 4.0–7.9 | 1200 |
Estimated total ammonia values needed to maintain PNH3 in the plasma and cutaneous intracellular fluid (ICF) at a value of 1200 μ Torr (1 Torr≈133.3 Pa) were calculated from estimates of plasma pH and the apparent dissociation constant(pK′) of total ammonia for the plasma or the cutaneous ICF,using the Henderson–Hassalbalch equation
Measured pH, total ammonia and NH3 partial pressure PNH3 gradients data taken from Litwiller et al.(Litwiller et al., 2006)
Apparent dissociation constants and solubility co-efficients for ammonia taken from Cameron and Heisler (Cameron and Heisler, 1983)
Plasma pH were estimated from regressions provided in Taylor et al.(Taylor et al., 1999)
Owing to the lack of available data on the intracellular pH of the cutaneous epithelium of fishes, the pH of this compartment was approximated using the physiological range reported in frog skin(Harvey and Ehrenfeld,1988)