Long term effects of thyroid stimulating hormone and insulin on intracellular pH in FRTL-5 cells

We have studied the chronic effects of TSH (100 μU/ml) and insulin (10 μg/ml) on intracellular pH (pH(i)) in FRTL-5 cells using the pH sensitive probe 2'7-bis (2-carboxyethyl-5'-6') carboxyfluorescein. FRTL-5 cells were cultured on Petri dishes either in the presence of 4H, ie. Coons F-12 containing cortisol (10 nM), transferrin (0.5 μg/ml), glycyl-histidyl lysine acetate (10 ng/ml) and somatostatin (10 μg/ml), or with 4H+insulin (5H), 4H+TSH, or 4H+TSH+insulin (6H). pH(i) was measured in small groups of cells by microspectrofluorimetry both in the presence and absence of bicarbonate ions after cells had been deprived of serum for at least a day. In the absence of TSH, insulin and bicarbonate ions, pH(i) was 7.26 ± 0.18) (mean ± SD, n = 49) rising to 7.89 ± 0.09 (n = 59) and 7.43 ± 0.1 (n = 55) in the presence of TSH (4H+TSH) and insulin (5H) respectively. Addition of both insulin and TSH (6H) resulted in a pH(i) of 7.75 ± 0.09 (n = 40). In the absence of TSH and insulin, but the presence of bicarbonate ions, pH(i) was 7.29 ± 0.12 (mean ± SD n = 47) rising to 7.72 ± 0.07 (n = 59) in 4H+TSH and 7.48 ± 0.08 (n = 60) in 5H. pH(i) in the presence of both TSH and insulin was 7.81 ± 0.03 (n = 60). In conclusion, both insulin and TSH caused an intracellular alkalinization, TSH markedly so, even in the presence of bicarbonate ions.