Characterization of Na+/H+ Antiporter Activity in PC-Cl3 Thyroid Cells.

Background/Aims: In thyroid cells, the intracellular pH plays a key role in the control of the iodide uptake, since iodide accumulation is associated with an intracellular acidification. In the present paper we studied the kinetic proprieties of the Na⁺/H⁺ antiporter (NHE) and the molecular expression of different NHE isoforms in rat thyroid PC-Cl3 cells. In addition the intracellular buffer capacity was also evaluated. Methods: pHi was measured using the pH sensitive fluorescent dye BCECF-AM. Amiloride, 5-(N,NDimethyl) hydrochloride was used to inhibit NHE activity. RT-PCR and western blot analyses were used to study the expression of NHE mRNA and protein isoforms. Results: PC-Cl3 cells shown a resting pHi, in the absence of CO₂/HCO₃ -, of 6.94 ± 0.1; after an acid load PC-Cl3 cells recovered toward resting pHi value, using a Na-dependent H⁺ extrusion mechanisms which was amiloride sensitive (K_i = 23 μM). The kinetic parameters were K(Na)app = 10 ± 2 mM and V_max = 0.23 ± 0.02 ΔpH/min x 10⁵ cells. NHE1, NHE2 and NHE3 were expressed at the mRNA level as well as at the protein level. Conclusion: PC-Cl3 cells express a functional Na/H exchange activity and different isoforms (NHE1, NHE2 and NHE3) are expressed in the plasma membrane. [ABSTRACT FROM AUTHOR]