Abstract

[14C]Dimethyloxazolidine-2,4-dione was used to determine the pH and bicarbonate concentration ([HCO3-]) in follicular cells and luminal fluid (LF) of turtle thyroids. Values of cellular and luminal pH and [HCO3-] were derived from the steady-state [14C]dimethyloxazolidine-2,4-dione values in whole gland and in the follicular LF sampled by micropipettes inserted into the follicular lumen and by resolution of the [14C]dimethyloxazolidine-2,4-dione uptake curve into its components by a computer program. In extracellular fluid of control turtles at 24 degrees C, the pH was 7.66, [HCO3-] was 33.1 mmol/l and pCO2 was 33.6 mm Hg. In thyroidal follicular cells, pH was 7.26 and [HCO3-] was 14.3 mmol/l; and in LF, pH was 7.32 and [HCO3-] was 16.5 mmol/l. These data provide evidence that H+ and HCO3- do not distribute according to their electrochemical gradients across both the basal and apical membranes of thyroid. Thyrotropin increased cell pH to 7.70 and [HCO3-] to 39.8 mmol/l; luminal pH and [HCO3-] were also markedly increased. Acetazolamide reduced [HCO3-] in both cells and LF. 4-Acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid increased cellular pH and [HCO3-] but did not alter these parameters in LF. Both ouabain and furosemide increased cellular pH and [HCO3-] and decreased luminal pH and [HCO3-]. Methimazole increased cellular pH and [HCO3-], decreased LF [HCO3-] and did not affect the LF pH.