K+ balance in rainbow trout gill and liver tissue, cell suspensions and cultured cells

Both intact gill and liver tissue from rainbow trout accumulated K+, as determined by 86Rb+ uptake, a process largely inhibited by ouabain, indicating the presence of functional NaKATPase. Cell suspensions, produced by disaggregation of gill or liver tissues, accumulated very little K+ compared to tissues (less than 10%). Disaggregation resulted in depolarisation of cells with loss of intracellular K+ and although NaKATPase, as measured by 86Rb+ uptake rate, remained functional and inhibitable by ouabain, the activity was insufficient to replace the rapid K+ loss. While attached, cultured gill and liver cells showed normal K+/Na+ ratios and NaKATPase activity, but release from the substratum resulted in depolarisation and rapid K+ loss as seen in cell suspensions. These results suggest that care is required in interpreting ionic regulatory and other results from cell suspensions and that further research should be directed towards systems where cells can maintain normal ionic balance.