Parathyroid hormone increases CFTR expression and function in Caco-2 intestinal epithelial cells

Abstract

Parathyroid hormone (PTH) enhances cystic fibrosis transmembrane conductance regulator (CFTR)-mediated anion secretion by the human intestinal epithelial cell line Caco-2. With the patch-clamp and Ussing chamber techniques, we investigated how PTH stimulates CFTR activity in Caco-2 cells. Cell-attached recordings revealed that PTH stimulated the opening of CFTR-like channels, while impedance analysis demonstrated that PTH increased apical membrane capacitance, a measure of membrane surface area. Using ion substitution experiments, the PTH-stimulated increase in short-circuit current (I_sc), a measure of transepithelial ion transport, was demonstrated to be Cl^-- and HCO₃^--dependent. However, the PTH-stimulated increase in I_sc was unaffected by the carbonic anhydrase inhibitor acetazolamide, but partially blocked by the intermediate-conductance Ca²⁺-activated K⁺ channel (IKCa) inhibitor clotrimazole. TRAM-34, a related IKCa inhibitor, failed to directly inhibit CFTR Cl^- channels in cell-free membrane patches, excluding its action on CFTR. In conclusion, PTH enhances CFTR-mediated anion secretion by Caco-2 monolayers by increasing the expression and function of CFTR in the apical membrane and IKCa activity in the basolateral membrane.

Keywords: Cystic fibrosis transmembrane conductance regulator (CFTR); Intermediate-conductance Ca(2+)-activated K(+) channel (IKCa); Ion secretion; Parathyroid hormone (PTH); Patch-clamp technique.