Effect of hypercapnia on intracellular pH regulation in a rainbow trout hepatoma cell line, RTH 149

Abstract

Fish exposed to elevated water CO(2) experience a rapid increase in blood CO(2) 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 (pH(i)) 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 pH(i) regulation. Employing the pH-sensitive fluoroprobe BCECF, the present study examined pH(i) regulation in RTH 149 under normocapnia and during extracellular acidification induced by either elevated CO(2) or 1M HCl. During exposure to hypercapnia, RTH 149 cells were acidified without recovery as long as the elevated CO(2) was maintained. In addition, rates of pH(i) recovery from NH(4)Cl-induced acidosis were significantly lower in cells exposed to hypercapnia or HCl compared to that in normocapnic cells, indicating that elevated CO(2) indirectly impeded pH(i) recovery through a reduction in pH(e) and/or pH(i). Moreover, pH(i) 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 pH(i) 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 pH(i) recovery rates relative to primary hepatocytes.