Effect of hypercapnia on intracellular pH regulation in a rainbow trout hepatoma cell line, RTH 149
Fish exposed to elevated water CO2 experience a rapid increase in blood CO2 levels (hypercapnia), resulting in acidification of both intra- and extra-cellular compartments. While the mechanisms associated with extracellular pH regulation have been well explored, much less is known about intracellular pH (pHi) regulation. There is great interest in developing non-animal models for research. One such model is the rainbow trout hepatoma cell line (RTH 149), which has been used to study a wide range of topics; however, no studies have investigated its potential use in pHi regulation. Employing the pH-sensitive fluoroprobe BCECF, the present study examined pHi regulation in RTH 149 under normocapnia and during extracellular acidification induced by either elevated CO2 or 1 M HCl. During exposure to hypercapnia, RTH 149 cells were acidified without recovery as long as the elevated CO2 was maintained. In addition, rates of pHi recovery from NH4Cl-induced acidosis were significantly lower in cells exposed to hypercapnia or HCl compared to that in normocapnic cells, indicating that elevated CO2 indirectly impeded pHi recovery through a reduction in pHe and/or pHi. Moreover, pHi regulation in RTH 149 was EIPA-sensitive, suggesting that an NHE may be involved. Overall, RTH 149 may have the potential for identifying transporters likely to play a role in pHi regulation in fish. However, it should not be used as a complete replacement for in vivo studies, especially to quantify acid–base regulatory ability at whole animal level, since RTH 149 appeared to have enhanced pHi recovery rates relative to primary hepatocytes.